Differential expression of K⁺ currents in mammalian retinal bipolar cells

Abstract

Whole-cell voltage-clamp recordings were performed to investigate voltage-dependent K⁺ currents in acutely isolated retinal cone bipolar cells (CBCs) from the rat. The physiological and pharmacological properties of the currents were compared with those in rod bipolar cells (RBCs). The K⁺ currents were found to be much larger in CBC than in RBCs. In addition, the currents in CBCs were activated and inactivated at more negative potentials. Based on the apparent inactivation property of the currents, CBCs were found to fall into two groups of cells that differed in the inactivation kinetics of I_K(V) but did not correlate to the ON- and OFF-type. The I_K(V) for the group of CBCs showing faster inactivation, as well as for all RBCs, contained two components with decay time constants around 0.1 and 1 s. The I_K(V) for the group of CBCs showing slower inactivation only contained the slower component. Furthermore, three components of I_K(V) were observed based on tetraethylammonium (TEA) sensitivity: high-sensitive, low-sensitive, and resistant component. The I_K(V) for a portion of CBCs showing faster inactivation, as well as for all RBCs, contained all three components. The I_K(V) for the remaining CBCs, including all of those CBCs showing slower inactivation, only contained the latter two components. This study reveals a differential expression of K⁺ currents in rat retinal bipolar cells, suggesting that K⁺ channels may play an important role in bipolar cell processing in mammalian retinas.