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Y-P Ma, Z Pan; Multiple Subtypes of Ca2+ Currents Contribute to the Spontaneous Regenerative Activities in Mammalian Retinal Bipolar Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3772.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To characterize the regenerative spontaneous activities and the underlying ionic mechanisms in mammalian retinal bipolar cells. Method: Patch-clamp recordings in whole-cell or perforated configurations were performed on acutely isolated retinal bipolar cells from ≥4-week-old rats. Intracellular Ca2+ concentrations were monitored by using Ca2+-sensitive dyes. Results: Under current-clamp with no or a small negative holding current (<-10 pA), isolated bipolar cells exhibit regular, spontaneous regenerative activities from a relative stable membrane potential around -80 mV. The shape and duration of the spontaneous waveforms for each cell are remarkably similar and could also be evoked by a brief depolarizing current. The waveforms, however, were found to be different between rod and cone bipolar cells. The spontaneous activities were also observed in the isolated axon terminals as well as in the isolated somas from rod bipolar cells. The latter are known to lack L-type Ca2+ currents. The spontaneous activities were accompanied by intracellular Ca2+ transients. The waveforms were reduced by nimodipine and enhanced by Bay K-8644. Blockade of potential Ca2+-induced Ca2+ release was not found to affect significantly the spontaneous activities or the waveforms. Application of mibefradil, a T-type Ca2+ channels antagonist, or Co2+ blocked the spontaneous activity. Conclusion: Isolated mammalian retinal rod and cone bipolar cells exhibit regenerative activities with distinct waveforms. The regenerative activities are triggered by T-type Ca2+ currents and the response waveforms are shaped by L-type Ca2+ currents. Both T- and L-type Ca2+ currents contribute to the regenerative property of mammalian bipolar cells.
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