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Signal integration at the pedicle of turtle cone photoreceptors: An anatomical and electrophysiological study

Published online by Cambridge University Press:  02 June 2009

Eric M. Lasater ,
Richard A. Normann  and
Helga Kolb
Eric M. Lasater
Affiliation:
Departments of Physiology and Ophthalmology, University of Utah, School of Medicine, Salt Lake City
Richard A. Normann
Affiliation:
Departments of Bioengineering, Physiology, and Ophthalmology, University of Utah, School of Medicine, Salt Lake City
Helga Kolb
Affiliation:
Departments of Physiology and Ophthalmology, University of Utah, School of Medicine, Salt Lake City
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Abstract

The morphology of the axon which connects the cell body and pedicle of turtle cone photoreceptors was studied by light and electron microscopy. The axon which contains numerous synaptic vesicles, some endoplasmic reticulum, and a few cisternae is basically filled with cytoplasm. The length of the axon is related to the class of cone and varies slightly with retinal location, with axons as short as 3–6 μm found in red cones, and as long as 60 μm in cones containing colorless oil droplets. By simultaneously voltage clamping the cell body and pedicle regions of single isolated cones, we measured the longitudinal axonal resistance and the cell body and pedicle membrane resistances. For each cell studied, the axonal resistance of cones with short axons was lower than the cell and pedicle membrane resistances. Thus, the cell can be considered to be an isopotential structure. However, in some cones with long axons, the axonal, cell body, and pedicle resistances were comparable. The pedicles of these cones, therefore, could act like summing points and may provide a locus for spatial signal integration. Electrical coupling between the principal and accessory members of double cones was also studied. Electron-microscopic observation of the membrane junction between the apposed inner segments of the double cones in the intact retina show narrow segments which resemble gap junctions. However, in every double cone studied in culture, passing currents into one member of the double cone did not result in measurable current flow in the adjacent cell. Thus, the two members of the double cone, isolated from the turtle retina, are not electrically coupled.

Keywords

Cone photoreceptorVoltage clampLsolated cellsInput resistanceCell body-pedicle coupling
Type
Research Article
Information
Visual Neuroscience , Volume 2 , Issue 6 , June 1989 , pp. 553 - 564
Copyright
Copyright © Cambridge University Press 1989

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