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Y. Ma, J. Cui, H. Hu, Z. Pan; Expression of Inwardly Rectifying K+ (Kir) Channels in Retinal Bipolar Cells . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4152.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Retinal bipolar cells have been reported to express hyperpolarization-activated cationic currents (Ih). We have previously observed a differential expression of Ih among different retinal bipolar cells in the rat (Hu & Pan, 2000 ARVO abstract). In this study, we report that retinal bipolar cells also express inwardly rectifying K+ current (IKir). Methods: Whole-cell patch-clamp recordings were performed in acutely isolated retinal bipolar cells and in bipolar cells in retinal slices from the rat. Results: Hyperpolarization steps evoked two types of inwardly rectifying currents. One was the previously reported Ih, which showed slow time-dependent activation. Consistently, Ih was carried by both Na+ and K+ ions and blocked by ZD7288, a selective blocker of Ih. The second current displayed rapid activation and no apparent inactivation. The current was carried by K+ ions. The activation threshold and the current-voltage relation shifted with a change in extracellular K+, a classical property of Kir channels. Furthermore, the current was found to be highly sensitive to Ba2+, a blocker of Kir channels. Retinal bipolar cells of different groups were found to differentially express IKir and Ih. A subset of CBCs showed only IKir. RBCs displayed mainly Ih. Conclusions: This is the first report of the expression of Kir channels in retinal bipolar cells. The differential expression of IKir and Ih in retinal bipolar cells may play a role in their diverse physiological functions.
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