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Ji Hyun Jeon, Sun-Sook Paik, In-Beom Kim; Ca2+ and Ca2+-activated Cl- currents of Presynaptic Terminals of Bipolar Cells: A Comparative Study on Mouse and Goldfish Retinas. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6152.
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© ARVO (1962-2015); The Authors (2016-present)
In our previous study, we identified and characterized Ca2+-activated Cl− currents (ICl(Ca)) in rod bipolar cells in the mouse retina. ICl(Ca) was preferentially localized in presynaptic terminals. Also, goldfish retinal bipolar cells have been well studied on the presynaptic localization of ICa and ICl(Ca). However, it is notable that their kinetics and pharmacological profiles are different among species. In this study, we investigated and compared the physiological properties of ICa and ICl(Ca) in bipolar cells dissociated from mouse and goldfish retinas.
The solitary bipolar cells in both mouse (C57BL/6J) and goldfish retinas were obtained with enzymatic dissociation. We measured the membrane currents of these cells by whole-cell voltage clamp using patch pipette.
In presynaptic terminal dissociated from mouse rod bipolar cell, depolarization produced a small transient ICa with maximal amplitude at about −20 mV. The mouse ICa was sensitive to Co2+, nifedipine and mibefradil. The depolarization of the cells to a voltage of +10 mV from a holding potential of −85 mV led to the generation of an inward current, which was followed by a slowly inactivating tail current (identified as ICl(Ca)). ICl(Ca) was abolished by treatment with the Cl− channel blockers, niflumic acid (NFA) and SITS. Contrary to mouse rod bipolar cells, goldfish ON-type bipolar cells had a big sustained ICa at a more positive potential range (> −20 mV) blocked by either Cd2+ or nifedipine. In ON-type bipolar cell terminals, we observed a very slowly declining inward ICl(Ca) after the termination of depolarizing voltage from a holding potential of −85 mV. This ICl(Ca) was partially blocked by SITS and not specific to NFA.
Mouse rod bipolar cell terminals showed the rather transient ICa current and slow ICl(Ca), while ON-type bipolar cell terminals of goldfish retina showed the sustained ICa and slower ICl(Ca). They may contribute to shape phasic and tonic responses of ganglion cells in goldfish and mouse retinas, respectively. These results suggest that presynaptic ICa and ICl(Ca) may act as important determinants of physiological properties in bipolar cells from one species to another.
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