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Chloride efflux inhibits single calcium channel open probability in vertebrate photoreceptors: Chloride imaging and cell-attached patch-clamp recordings

Published online by Cambridge University Press:  01 March 2000

WALLACE B. THORESON
Affiliation:
Department of Ophthalmology, University of Nebraska Medical Center, Omaha
RON NITZAN
Affiliation:
Department of Physiology and Graduate Program in Neuroscience, University of Minnesota, Minneapolis
ROBERT F. MILLER
Affiliation:
Department of Physiology and Graduate Program in Neuroscience, University of Minnesota, Minneapolis

Abstract

The present study uses cell-attached patch-recording techniques to study the single-channel properties of Ca2+ channels in isolated salamander photoreceptors and investigate their sensitivity to reductions in intracellular Cl. The results show that photoreceptor Ca2+ channels possess properties similar to L-type Ca2+ channels in other preparations, including (1) enhancement of openings by the dihydropyridine agonist, (−)BayK8644; (2) suppression by a dihydropyridine antagonist, nisoldipine; (3) single-channel conductance of 22 pS with 82 mM Ba2+ as the charge carrier; (4) mean open probability of 0.1; (5) open-time distribution fit with a single exponential (τ0 = 1.1 ms) consistent with a single open state; and (6) closed time distribution fit with two exponentials (τc1 = 0.7 ms, τc2 = 25.4 ms) consistent with at least two closed states. Using a Cl-sensitive dye to measure intracellular [Cl], it was found that perfusion with gluconate-containing, low Cl medium depleted intracellular [Cl]. It was therefore possible to reduce intracellular [Cl] by perfusion with a low Cl solution while maintaining the extracellular channel surface in high Cl pipette solution. Under these conditions, the single-channel conductance was unchanged, but the mean open probability fell to 0.03. This reduction can account for the 66% reduction in whole-cell Ca2+ currents produced by perfusion with low Cl solutions. Examination of the open and closed time distributions suggests that the reduction in open probability arises from increases in closed-state dwell times. Changes in intracellular [Cl] may thus modulate photoreceptor Ca2+ channels.

Type
Research Article
Copyright
2000 Cambridge University Press

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