Ca(2+)-dependent Cl- current at the presynaptic terminals of goldfish retinal bipolar cells.
In ON-type bipolar cells dissociated from the goldfish retina, a slowly declining inward current (Itail) was observed after the termination of depolarizing voltage step commands, during which a Ca2+ current was elicited. The properties of Itail were investigated under the whole-cell voltage clamp. Introduction of the membrane permeant Ca2+ chelator, BAPTA/AM, into the cell suppressed Itail, indicating that Itail was activated by the increase of intracellular free Ca2+ concentration ([Ca2+]i). The major component of Itail was identified as the Ca(2+)-dependent Cl- current (ICl(Ca)), since the reversal potential of Itail was almost identical to the Cl- equilibrium potential at various extracellular Cl- concentrations ([Cl-]o). The contribution of the Na+/Ca2+ exchanger current to Itail was very small. ICl(Ca) was partially suppressed by 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) when it was locally applied to the axon terminal but not to the cell body region, suggesting that Ca(2+)-dependent Cl- channels were localized to the axon terminal. The relationship between the peak amplitude of ICl(Ca) and the amount of charge carried by the Ca2+ current was almost linear at levels less than ca. 50 pC, but became saturated at a higher Ca2+ charge.
Department of Psychology, Faculty of Letters, University of Tokyo, Japan.
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Okada
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Horiguchi
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Tachibana
D000818:Animals; D002118:Calcium / Q000502:physiology*; D018118:Chloride Channels / Q000187:drug effects*; D006054:Goldfish; D008564:Membrane Potentials / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology*; D012160:Retina / Q000502:physiology*; D013997:Time Factors
D018118:Chloride Channels; D002118:Calcium