The Journal of Neuroscience, July 1, 1999, 19(13):5195-5204
A Zinc-Dependent Cl
Current in Neuronal Somata
Toshihide
Tabata and
Andrew T.
Ishida
Section of Neurobiology, Physiology, and Behavior, University of
California, Davis, California 95616-8519
Extracellular Zn2+ modulates current passage
through voltage- and neurotransmitter-gated ion channels, at
concentrations less than, or near, those produced by release at certain
synapses. Electrophysiological effects of cytoplasmic
Zn2+ are less well understood, and effects have been
observed at concentrations that are orders of magnitude greater than
those found in resting and stimulated neurons. To examine whether and
how neurons are affected by lower levels of cytoplasmic
Zn2+, we tested the effect of
Zn2+-selective chelators,
Zn2+-preferring ionophores, and exogenous
Zn2+ on neuronal somata during whole-cell
patch-clamp recordings. We report here that cytoplasmic zinc
facilitates the downward regulation of a background
Cl
conductance by an endogenous protein kinase C
(PKC) in fish retinal ganglion cell somata and that this regulation is
maintained if nanomolar levels of free Zn2+ are
available. This regulation has not been described previously in any
tissue, as other Cl
currents have been described
as reduced by PKC alone, reduced by Zn2+ alone, or
reduced by both independently. Moreover, control of cation currents by
a zinc-dependent PKC has not been reported previously. The regulation
we have observed thus provides the first electrophysiological
measurements consistent with biochemical measurements of zinc-dependent
PKC activity in other systems. These results suggest that contributions
of background Cl
conductances to electrical
properties of neurons are susceptible to modulation.
Key words:
background chloride conductance; resting potential; outward rectification; PKC; Zn2+; divalent
cation
Copyright © 1999 Society for Neuroscience 0270-6474/99/19135195-10$05.00/0