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Z-H Pan, Y MA; Voltage-Dependent K+ and Na+ Currents Contribute to the Response Properties of Mammalian Retinal Bipolar Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3770.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously reported that mammalian cone bipolar cells express much larger K+ currents than rod bipolar cells and have also shown that a subset of cone bipolar cells express Na+ currents. Here, we investigated the possible roles of these currents in shaping bipolar cell response properties. Methods: Whole-cell patch-clamp recordings were performed on isolated bipolar cells or bipolar cells in retinal slices from ≥4-week-old rats. The effects of K+ and Na+ channel blockers were examined on the spontaneous regenerative waveforms and the current-injection-evoked responses of these cells. Results: Isolated bipolar cells exhibit spontaneous regenerative activities. The regenerative waveforms of rod and cone bipolar cells were found to be distinct. The waveforms of rod bipolar cells displayed a more depolarizing potential and a longer duration than those of cone bipolar cells. In addition, a subset of cone bipolar cells exhibits a TTX-sensitive action potential. Current injection evoked a fixed plateau of the voltage response for both rod and cone bipolar cells. The plateau of the voltage response in rod bipolar cells was again found to be more positive than that observed in cone bipolar cells. Application of TEA and 4-AP increased the amplitude of the spontaneous waveform and the evoked voltage response in both types of bipolar cells. Action potentials were also observed by current-injection in many cone bipolar cells. The rise time of the evoked voltage response in these cone bipolar cells was significantly shorter than that observed in rod bipolar cells. Conclusion: The voltage response of bipolar cells is capped by K+ currents. Na+ currents speed up the kinetics of the voltage response in cone bipolar cells. Our results suggest that K+ and Na+ currents play an important role in defining the different response properties between mammalian rod and cone bipolar cells.
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