In a previous report, it has been shown that water deprivation significantly affects the two-bottle taste preferences and one-bottle taste acceptance in rats when no food was available during tests. Since no food was available, the course of drinking was never interrupted by eating. Theoretically, if a rat faces a simultaneous choice between food and fluid, and if the course of drinking is interrupted by eating, these conditions might interfere with taste preferences, total fluid intake and eating in thirsty rats. The aims of the present experiments were: to ascertain whether food intake during both two-bottle preference and one-bottle acceptance tests in thirsty rats might be influenced by the palatability of the solutions; to verify whether the availability of food during tests influences taste preference and acceptance, and total fluid intake; to detect variations induced by dehydration on body weight and some plasma and urinary parameters that might interfere with food and fluid intake, taste preference and acceptance. Using naive rats, five groups of rats showing the same taste preferences for one of four prototypical tastes and water were selected. Then, both two-bottle preference (Expt 1) and one-bottle acceptance tests (Expt 2) were performed in rats deprived of water for either 12, 24, 36 or 48 h. The results showed that in both Expt 1 and Expt 2, inhibition of feeding and decrease of body weight during dehydration was very similar in all rats. The presence of food during the tests did not affect taste preference and acceptance. During Expt 1, after severe water deprivation (36 and 48 h), food intake was related to the palatability of the solution paired with water. When rats drank either NaCl or sucrose, they ate less food than rats drinking HCl, quinine, or water. In Expt 2, rats drinking NaCl solution as the only source of fluid ate significantly less food than all other groups. The intake of sucrose and/or NaCl solutions be may explained by two different post-ingestion effects (energetic and osmotic). Since rats drinking either sucrose or NaCl ate less food but drank more fluid, they had a significantly higher fluid/food intake ratio than that of rats who drank water, quinine, or HCl, who ate more food but drank less fluid. The increase of the fluid/food intake ratio in rats drinking sucrose or NaCl was directly correlated with the length of dehydration. Self-denial of food during dehydration may be responsible for overeating and overdrinking during the recovery period after tests. After dehydration lasting for 24 and 48 h, plasma [Na+], [protein], osmolality and haematocrit values increased but [K+] decreased. Urinary volume decreased but urinary [Na+] increased. These results are related to food and fluid intake, taste preference and acceptance after dehydration periods. Experimental Physiology (2001) 86.4, 489-498.

Experiments were performed on twenty-two neurologically normal subjects in order to investigate the effects of skin brushing on H reflex excitability in triceps surae. H reflex amplitude was observed to decrease during brushing of a 2 cm × 10 cm area of skin overlying triceps surae, returning to control levels when brushing ceased. Alterations in the duration of the brushing period did not affect the magnitude of the H reflex inhibition, although increased frequency of brush strokes per minute slightly increased the amount of inhibition observed. Brushing of smaller skin areas overlying the muscle only sometimes resulted in H reflex inhibition. Brushing over other skin areas of the lower limb produced only slight effects on triceps surae H reflex amplitude. Removal of cutaneous input from the skin overlying triceps surae abolished any effects of brushing in this area on H reflex amplitude. These results demonstrate an inhibitory effect of brushing on H reflex excitability in normal subjects. If such results are confirmed in subjects with neurological deficit, they could have implications for the use of brushing in clinical practice.

Transmission electron microscopic techniques were used to carry out a quantitative analysis of the density of fenestration in the inner medullary vasa recta of the rat kidney. Measurements were made at 200 µm intervals from the tip to the base of the papilla (1800 µm from the tip). Fenestral diaphragms were estimated to be 65·4 ± 0·78 nm in diameter (mean ± S.E.M.), and were arranged in plaques with a mean interfenestral distance of 114·8 ± 2·6 nm. Near the tip of the papilla there was no correlation between vessel size and degree of fenestration; density of fenestration, however, began to decrease about 1400 µm from the tip. The ratio of fenestrated to non-fenestrated profiles of vasa recta was found to be linear with respect to distance from the tip (r = 0·991), with values ranging from about 40 : 1 near the tip to 2 : 1 near the base of the papilla. We have estimated the proportion of the total surface area of a fenestrated vasa recta occupied by fenestral diaphragms to be 0·057 at 1000 µm from the tip. The total potential conductance (K) of a 200 µm segment of fenestrated vessel at 1000 µm from the tip was calculated to be 0·319 µm3 s-1 cmH2O-1, giving a hydraulic conductivity (Lp) of 0·030 µm s-1 cmH2O-1. We have also examined the reverse question of the conductance of a single fenestra if all the fluid flux across the vessel wall occurred through the fenestrae and none via the intercellular clefts or water channels; single fenestral conductance was estimated to be 1·94 × 10-3 µm3 s-1 cmH2O-1.

Earlier work in this laboratory showed that noradrenaline (NA) induces apoptosis in primary cultures of alveolar epithelial cells (AECs). Apoptosis of alveolar epithelial cells may promote the collapse of lung barrier function. On this basis we hypothesized that exogenous NA, administered by intratracheal (I.T.) instillation, might induce AEC apoptosis in vivo followed by acute lung injury. Delivery of NA (10 µM) I.T. into male Wistar rats increased labelling of both fragmented DNA, measured by in situ end labelling (ISEL), and the active form of caspase 3 (anti-Casp3) 6 and 20 h after administration (P < 0.05), but instillation of the vehicle alone (PBS) had no effect. Both ISEL and anti-Casp3 labelling were attenuated by concurrent I.T. delivery of the broad-spectrum caspase inhibitor ZVADfmk. After 6 h, most ISEL- and Casp3-positive cells were located in the surfaces of alveolar walls, but after 20 h more were found in alveolar spaces (P < 0.05). Instillation of NA also increased the bronchoalveolar lavage (BAL) content of fluorescent albumin (BODIPY-alb), which had previously been injected intravenously; the increase was reversed by concurrent ZVADfmk administration. These data suggest that NA-induced apoptosis of AECs in vivo is sufficient to invoke transient collapse of AEC barrier function that is rapidly repaired. Experimental Physiology (2003) 88.2, 269-275.

In rings of rat iliac artery, contractions were evoked by noradrenaline (NA), the selective α1 adrenoceptor agonist phenylephrine (PE), and K+, which causes depolarisation-induced contraction. There was no evidence of α2 adrenoceptor-evoked contraction. Hypoxia, induced by reducing PO2 in the bath from 100 mmHg to 70, 55 or 40 mmHg, had similar effects on rings with (E+) and without (E-) endothelium. In E- rings, the NA concentration-response curve was biphasic, whereas that for PE was monophasic. Hypoxia reduced maximum contractions in response to NA and PE (NAmax and PEmax, respectively) without affecting the concentrations that evoked 50 % of maximum contraction (EC50). At PO2 of 70 mmHg, NAmax of the high affinity α1 receptor for NA (NAmaxh) and PEmax were reduced by ~15 %, but at PO2 of 55 and 40 mmHg, NAmaxh was severely attenuated while PEmax fell by 45 and 75 %, respectively. Similarly, the Ca2+ channel blocker nicardipine depressed NAmaxh and PEmax, but PO2 of 55 mmHg further reduced NAmax and PEmax. Hypoxia also reduced contractions evoked by NA, PE or K+ at the concentrations required to produce 80 % of the maximum contraction (EC80), receptor-mediated contractions being more affected. Ca2+-free conditions reduced the contractions evoked by NA and PE, at the EC80, to ~10 % of control. The K+ channel inhibitors glibenclamide and tetraethylammonium did not prevent hypoxia-induced depression of PE-evoked contraction. Thus, contractions evoked in iliac artery by the high affinity subtype of α1 adrenoceptor for NA, which may respond to circulating levels of NA, and by the single α1 adrenoceptor subtype for PE, are especially vulnerable to PO2 levels ≤ 55 mmHg. We propose that this reflects hypoxia-induced inhibition of Ca2+ influx through L-type and receptor-operated Ca2+ channels; K+ channel opening makes little contribution. Experimental Physiology (2002) 87.2, 171-184.

In the present study, we have investigated the viability of using tetrodotoxin (TTX) to induce selective blockade of myelinated fibre conduction in rabbit sural nerve, and explored some aspects of reflexes evoked by non-myelinated sural nerve afferents before and after application of TTX. In rabbits decerebrated under halothane-nitrous oxide anaesthesia, application of 30 nM TTX to the desheathed sural nerve completely blocked Aβ and Aδ waves of the compound action potential evoked by electrical stimulation of the nerve at 95 times threshold. The amplitude of C-fibre volleys evoked by these stimuli was reduced to a mean of 60 % of pre-treatment values. Reflexes evoked in medial gastrocnemius motoneurones by sural nerve stimulation showed corresponding changes after TTX treatment, with activation latency increasing from 5-7 ms in the control state to > 100 ms after TTX application. Temporal summation (wind up) in long latency reflexes (> 100 ms) was significantly enhanced after application of TTX. These data show that low concentrations of TTX can selectively block conduction in rabbit sural nerve A-fibres, providing a method for studying the central actions of non-myelinated C-fibres in isolation. Experimental Physiology (2003) 88.1, 13-18.

When faced with stress, an organism calls upon several mechanisms to maintain biological homeostasis. The cardiovascular system is the first to respond usually with an increase in arterial pressure and tachycardia. Therefore we investigated the central and peripheral sympathetic responses to acute and chronic starvation in Wistar rats. The noradrenaline (NA) turnover rate was determined in different catecholaminergic nuclei (A1, A2, A5, A6) as well as the arterial blood pressure and heart rate modifications. During acute starvation (3 days of starvation), the NA turnover was increased in the A1 and rostral A2 nuclei as well as in ventricles and kidneys and decreased in the A6 nucleus. During chronic starvation (4 consecutive cycles of 3 days of starvation plus 1 day of feeding), the NA turnover was increased in the A5 and caudal A2 nuclei as well as in ventricles and atria and decreased in the A1 nucleus and kidneys. The arterial blood pressure revealed a gradual decrease during the first 3 days of fasting but the heart rate was not modified. We conclude that starvation should be considered as an unusual state of stress because of the absence of locus coeruleus response (A6 nucleus) despite its well-defined role in stress reactions. One of the manifestations of these central and peripheral noradrenergic changes is the change in blood pressure during the starvation-feeding cycles.

Newborn pigs rely essentially on shivering thermogenesis in the cold. In order to understand the rapid postnatal enhancement of thermogenic capacities in piglets, the oxygen and nutrient uptake of hindquarters was measured in vivo in 1- (n = 6) and 5-day-old (n = 6) animals at thermal neutrality and during cold exposure. The hindquarters were considered to represent a skeletal muscle compartment. Indirect calorimetry and arterio-venous techniques were used. The cold challenge (23¡C at 1 day old and 15¡C at 5 days old for 90 min) induced a similar increase (+90 %) in regulatory heat production at both ages. Hindquarters blood flow was higher at 5 days than 1 day old at thermal neutrality (26 ± 3 vs. 17 ± 1 ml min-1 (100 g hindquarters)-1) and its increase in the cold was much more marked (+65 % at 5 days old vs. +25 % at 1 day old). Oxygen extraction by the hindquarters rose from 30-35 % at thermal neutrality to 65-70 % in the cold at both ages. The calculated contribution of skeletal muscle to total oxygen consumption averaged 34-40 % at thermal neutrality and 50-64 % in the cold and skeletal muscle was the major contributor to regulatory thermogenesis. Based on hindquarters glucose uptake and lactate release, carbohydrate appeared to be an important fuel for shivering. However, net uptake of fatty acids increased progressively during cold exposure at 5 days old. The enhancement in muscular blood supply and fatty acid utilization during shivering is probably related to the postnatal improvement in the thermoregulatory response of the piglet.

The Na+-K+-2Cl- cotransporter (NKCC1) is responsible for ion transport across the secretory and absorptive epithelia, the regulation of cell volume, and possibly the modulation of cell growth and development. It has been reported that a variety of cells, including osteoblasts, contain this cotransporter. In this study, the physiological role of NKCC1 in osteoclastogenesis was exploited in a co-culture system. Bumetanide, a specific inhibitor of NKCC1, reduced the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. In order to investigate the mechanism by which bumetanide inhibits osteoclastogenesis, the mRNA expressions of the receptor activator of nuclear factor (NF)-κB ligand (RANKL) and osteoprotegerin (OPG) were analysed by RT-PCR. Exposure of osteoblastic cells to a medium containing 1 µM bumetanide reduced RANKL mRNA expression induced by 10 nM 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3, in a dose-dependent manner. In addition, RANKL expression was also analysed with enzyme-linked immunosorbant assay (ELISA) using anti-RANKL antibody. The expression of RANKL was decreased with the increase of bumetanide concentration. In contrast, the expression of OPG mRNA, a novel tumour necrosis factor (TNF) receptor family member was increased in the presence of bumetanide. These results imply that bumetanide inhibits osteoclast differentiation by reducing the RANKL/OPG ratio in osteoblastic cells. However, no significant difference in M-CSF mRNA expression was observed when bumetanide was added. Also, we found that the phosphorylation of c-Jun NH2-terminal kinase (JNK), which regulates the activity of various transcriptional factors, was reduced by bumetanide treatment. Conclusively, these findings suggest that NKCC1 in osteoblasts has a pivotal role in 1α,25(OH)2D3-induced osteoclastogenesis partly via the phosphorylation of JNK. Experimental Physiology (2003) 88.5, 569-574.

The present study was planned to investigate the effect of left ventricular pressure and inotropic state on coronary arterial inflow in systole in the anaesthetized dog. A wide range of left ventricular systolic pressures, including the physiological range, were studied. Experiments were done under conditions of maximal vasodilatation and low perfusion pressure in order to avoid vascular autoregulative interference and to keep the microvascular pressure within the normal range. In five anaesthetized dogs, perfused with extracorporeal circulation system, ventricular volume was changed from 20 to 50 ml in steps of 10 ml by filling an intraventricular latex balloon, and the related changes in left ventricular pressure and coronary flow were measured. The volume was then extended to 70 ml to obtain an overstretch which induced a transient decrease in cardiac contractility. During the period of low cardiac contractility the volume was brought back to 20 ml in steps of 10 ml. Systolic ventricular pressure changed with volume but was lower during the period of low contractility. For systolic pressures below 100 mmHg there was no significant relationship between pressure and coronary systolic flow, but the relationship shifted to higher flows during low contractility. For systolic pressures above 100 mmHg systolic coronary flow decreased significantly when systolic pressure increased. In this case the slopes of the relationships were not significantly different before and after the reduction in contractility. These findings suggest that for systolic pressures less than 100 mmHg (i.e. below the physiological range) the shielding effect of the contracting ventricle prevents the ventricular pressure from being transmitted in the myocardial wall. When systolic pressure exceeds 100 mmHg the shielding effect is overcome and the amplitude of the systolic flow reduction varies with ventricular pressure.

A method of telemetric measurement of antroduodenal myoelectrical activity (EMG) in freely moving pigs has been developed. Silver bipolar electrodes were sutured on the antrum and duodenum and connected to a telemetry transmitter implanted extraperitoneally between the abdominal muscles. The EMG signals were collected by a receiver, filtered, amplified and archived by a computer. The telemetric EMG signal did not differ from that obtained with a conventional wire method. Substantial differences between day and night migrating myoelectric complex (MMC) patterns were found. The advantages of telemetric EMG recording make it a useful tool for long-term recording of antroduodenal EMG.

This study examined the role of muscarinic parasympathetic mechanisms in generating the progressive increases in ventilation (V˙E) and heart rate previously reported with 8 h exposures to hypoxia. The sensitivities of V˙E (Gp) and heart rate (GHR) to acute variations in hypoxia, and V˙E and heart rate during acute hyperoxia were assessed in 10 subjects before and after two 8 h exposures to isocapnic hypoxia (end-tidal PO2 = 50 mmHg). The responses were measured during muscarinic blockade with glycopyrrolate (0.015 mg kg-1) and without glycopyrrolate, as a control. There were significant increases in Gp (P < 0.01) and V˙E during hyperoxia (P < 0.01) following hypoxic exposure, but these were unaffected by glycopyrrolate. GHR increased significantly by 0.29 ± 0.08 beats min-1 %-1 (mean ± S.E.M.) following exposure to hypoxia under control conditions, but only non-significantly by 0.10 ± 0.08 beats min-1 %-1 with glycopyrrolate. This difference was significant. Changes in heart rate during hyperoxia were slight and inconclusive. We conclude that muscarinic mechanisms play little role in the progressive ventilatory changes that occur over 8 h of hypoxia, but that they do mediate much of the progressive increase in heart rate. Experimental Physiology (2001) 86.4, 529-538.

Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (V˙O2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, V˙O2, ventilatory rate (V˙E), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 ± 13.9 s), ischaemia quickened the V˙O2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 ± 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min V˙O2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the V˙O2 time course. Reactive hyperaemia induced a faster V˙O2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia. Experimental Physiology (2002) 87.2, 227-235.

Oscillations in the cardiovascular system have been observed in patients with periodic breathing. It is not clear whether these are driven by primary oscillations in the respiratory system or whether an intrinsic cardiovascular instability is required, as previous studies with subjects performing voluntary periodic breathing have failed to produce the cardiovascular oscillations. We investigated whether cardiovascular oscillations occurred in healthy controls performing voluntary periodic breathing. Six healthy subjects performed voluntary periodic breathing with guidance from a real-time computer display. We measured ventilation, end-tidal partial pressures of O2 (PO2) and CO2 (PCO2), heart rate, blood pressure (BP), arterial oxygen saturation and stroke volume and cardiac output by transthoracic impedance cardiography. Fourier analysis was used to quantify the size and phase of the periodic breathing-induced oscillations in these parameters. Periodic breathing (amplitude 30 % of mean ventilation) induced oscillations in end-tidal PO2 (amplitude 0.8 kPa), end-tidal PCO2 (amplitude 0.3 kPa), R-R interval (amplitude 32.6 ms), systolic BP (amplitude 3 mmHg), diastolic BP (amplitude 3 mmHg), stroke volume (amplitude 8.0 ml, mean 79.5 ml) and cardiac output (amplitude 0.6 1, mean 5.9 l min-1). The oscillations in stroke volume and cardiac output were nearly in phase with ventilation, with their peaks occurring 5.6 and 6.1 s, respectively, after the peak in ventilation. An oscillatory ventilatory pattern entrains the cardiovascular system in healthy controls into fluctuations, not only in heart rate and BP, but also in stroke volume and cardiac output

Connexins (Cx) form intercellular junctional channels which are responsible for metabolic and electrical coupling. We report here on the biochemical and immunohistochemical characterization of zebrafish connexin zfCx43.4, an orthologue of mammalian and avian Cx45, and the electrophysiological properties of junctional channels formed by this protein. The investigations were performed on transfected COS-7 cells or HeLa cells. Using site-directed antibodies, zfCx43.4 cDNA (GenBank accession no. X96712) was demonstrated to code for a protein with a Mr of 45 000. In transfected cells, zfCx43.4 was localized in cell-cell contact areas as expected for a gap junction protein. zfCx43.4 channels were shown to transfer Lucifer Yellow. The multichannel currents were sensitive to the transjunctional voltage (Vj). Their properties were consistent with a two-state model and yielded the following Boltzmann parameters for negative/positive Vj: Vj,0 = -38.4/41.9 mV; gj,min = 0.19/0.18; z = 2.6/2.3. These parameters deviate somewhat from those of zfCx43.4 channels expressed in Xenopus oocytes and from those of Cx45, an orthologue of zfCx43.4, expressed in mammalian cells or Xenopus oocytes. Conceivably, the subtle differences may reflect differences in experimental methods and/or in the expression system. The single channel currents yielded two prominent levels attributable to a main conductance state (γj,main = 33.2 ± 1.5 pS) and a residual conductance state (γj,residual = 11.9 ± 0.6 pS). Experimental Physiology (2003) 88.6, 681-690.

Electrical stimulation of the parasympathetic auriculo-temporal nerve (40 Hz, 30 min), in the anaesthetized rat under α- and β-adrenoceptor blockade, increased [3H]thymidine and [3H]leucine uptake into the parotid glands by 80 and 263 %, respectively. The increase in response to parasympathetic stimulation was almost the same ([3H]thymidine 82 % and [3H]leucine 283 %) when atropine (2 mg kg-1 I.P. or I.V.) was included in the pretreatment. Neither intravenous infusion of vasoactive intestinal peptide (0.5-20 mg kg-1 min-1, 30 min) nor of bethanechol (10 mg kg-1 min-1, 30 min), under adrenoceptor blockade, increased the uptake of [3H]thymidine into the glands. However, these drugs increased [3H]leucine uptake, and in combination they interacted positively. Whereas vasoactive intestinal peptide is likely to be involved in the parasympathetic nerve-evoked protein synthesis, the nature of the non-adrenergic, non-cholinergic component(s) involved in the mitogenic response is presently unknown.

The actions of arachidonic acid (AA) were investigated in guinea-pig isolated ventricular myocytes. Exposure of myocytes to 10 µM AA reduced the amplitude of contractions and calcium transients accompanying action potentials at a frequency of 1 Hz. AA (10 µM) also reduced the amplitude of calcium currents recorded under voltage-clamp conditions. The suppression of contraction by AA was not prevented by either 10 µM trihydroindomethicin (to inhibit cyclo-oxygenase) or 10 µM ETYA (5,8,11,14-eicosatetraynoic acid, to inhibit AA metabolising enzymes), showing that the actions of AA appeared not to be mediated by these metabolites. The reduction of contraction by 10 µM AA was also not prevented by the protein kinase C inhibitor, Ro31-8220 (1 µM), showing that this pathway appeared not to be required for the observed effect. Direct effects of AA may be involved. A further action of 10 µM AA was to suppress spontaneous electrical activity induced by either the β-adrenergic agonist isoprenaline or the Na+ pump inhibitor, ouabain. This effect of AA on spontaneous activity might be associated with the observed reduction of calcium entry through L-type calcium channels, although additional effects of AA on calcium release from the sarcoplasmic reticulum might also be involved. Experimental Physiology (2001) 86.4, 437-449.

Electrophysiological investigation of neurones in sacral segments of the spinal cord was performed in [alpha]-chloralose-anaesthetized cats in order to establish whether at least some ascending tract neurones could diverge to three different centres located in the brainstem, the cerebellum or the spinal cord. Recordings of antidromic action potentials from cells in S1 and S2 segments were taken following stimulation of the contralateral gigantocellular nucleus, contralateral restiform body and ipsi- and contralateral grey matter of the C6 spinal segment. Antidromic responses allowed identification of several types of neurones that differed in their pattern of supraspinal or propriospinal projections. In eighteen out of a total of sixty-three neurones triple projections to all the above structures were found. In the majority of cells investigated their axons divided into two branches ascending both ipsi- and contralaterally in the lateral funiculi of the spinal cord. Their cell bodies were distributed in laminae VII-VIII except for a minor group of neurones that projected to the C6 segment only, which were located in laminae V-VI. The latter group also displayed lower values of axonal conduction velocities. Comparison of conduction velocities in proximal and distal parts of axons revealed significant slowing in most, raising the possibility that additional collaterals were present to other spinal or supraspinal centres. Dual and triple projections from most cells in this study suggest that such a divergence may be a more common feature of ascending tract neurones than has been reported before.

Adrenoceptor stimulation enhances repolarising and depolarising membrane currents to different extents in cardiac myocytes. We investigated the opposing effects of the repolarising Ca2+-activated Cl- current (ICl(Ca)) and depolarising L-type Ca2+ current (ICa,L) on the action potential configuration of sheep ventricular myocytes stimulated with noradrenaline. Whole-cell current-clamp recordings revealed that noradrenaline accelerated and prolonged phase-1 repolarisation. We define the minimal potential at the end of phase-1 repolarisation as 'notch level'. Noradrenaline (1 µM) caused the notch level to fall from 14 ± 2.6 to 7.8 ± 2.8 mV (n = 24), but left action potential duration, resting membrane potential or action potential amplitude unaffected. Whole-cell voltage-clamp recordings showed that 1 µM noradrenaline increased both ICa,L and ICl(Ca), but it had no significant effect on the principal K+ currents. Blockage of ICl(Ca) by 0.5 mM 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) in both the absence and the presence of noradrenaline abolished phase-1 repolarisation. In the presence of noradrenaline, DIDS caused elevation of the plateau phase amplitude and an increase in the action potential duration. In conclusion, elevation of the plateau phase amplitude and action potential prolongation associated with an increased ICa,L upon adrenoceptor stimulation is prevented by an increased ICl(Ca) in sheep ventricular myocytes. Experimental Physiology (2001) 86.2, 151-159.

It was recently demonstrated that ammonia inhibits sodium absorption in the proximal colon of rats. In order to investigate the effect of luminal ammonia in the distal colon, sodium and chloride transport were measured in Ussing chambers. Under short-circuit conditions, distal colon absorbed sodium and chloride. When luminal ammonia (30 mmol l-1) was present, sodium and chloride absorption was diminished. Inhibition of the two Na+-H+ exchanger isoforms NHE2 and NHE3, which are known to be located in the apical membrane of the distal colon epithelium, failed to influence the effect of ammonia on transepithelial sodium and chloride fluxes. The inhibitory effect of ammonia was eliminated under the following conditions: after block of carbonic anhydrases with acetazolamide, in the presence of an unspecific blocker of Na+-H+ exchangers, and under chloride-free conditions. Ammonia did not alter electrogenic sodium absorption. These results demonstrate that luminal ammonia inhibits sodium and chloride absorption in rat distal colon. We suggest that ammonia inhibits NaCl absorption by interfering with a Na+-H+ exchanger that is not NHE2 or NHE3. Experimental Physiology (2002) 87.3, 311-319.