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Modulation of A-type potassium currents in retinal horizontal cells by extracellular calcium and zinc

Published online by Cambridge University Press:  04 October 2006

DAO-QI ZHANG ,
ZIYI SUN  and
DOUGLAS G. MCMAHON
DAO-QI ZHANG
Affiliation:
Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
ZIYI SUN
Affiliation:
Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
DOUGLAS G. MCMAHON
Affiliation:
Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
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Abstract

Extracellular Ca2+ and Zn2+ influence many aspects of retinal function. Here, we examined the effect of external Ca2+ and Zn2+ on potassium channels of retinal horizontal cells. When extracellular Ca2+ was lowered from 3 mM to 0.3 mM, horizontal cell transient outward currents elicited by voltage steps from resting membrane potential (−70 mV) were decreased by approximately 50%, whereas the sustained currents remained unchanged. This effect was due to a hyperpolarizing shift in the steady-state inactivation curve of A-type K+ currents when extracellular Ca2+ concentration was lowered. The mean half inactivation potential of the steady-state inactivation curves was hyperpolarized from −56.3 ± 4.7 mV in 3 mM Ca2+ to −76.4 ± 3.9 mV in 0.3 mM Ca2+. Neither the state-steady activation curve nor the kinetics of inactivation was significantly changed in low extracellular Ca2+. The addition of 30 μM Zn2+ restored peak outward currents in 0.3 mM Ca2+. The half inactivation voltages were depolarized from −70 ± 2.8 mV in 0.3 mM Ca2+ to −56 ± 2.6 mV in 0.3 mM Ca2+ plus 30 μM Zn2+. Taken together, the results indicate that external Ca2+ and Zn2+ maintain the activity of A-type potassium channels in retinal horizontal cells by influencing the voltage dependence of steady-state inactivation.

Keywords

Potassium channelsDivalent cationsPatch clampSignal transmissionRetina
Type
Research Article
Information
Visual Neuroscience , Volume 23 , Issue 5 , September 2006 , pp. 825 - 832
Copyright
2006 Cambridge University Press

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