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The Journal of Neurophysiology Vol. 84 No. 3 September 2000, pp. 1123-1135
Copyright ©2000 by the American Physiological Society
Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
Prakriya, Murali and
Christopher J. Lingle.
Activation of BK Channels in Rat Chromaffin Cells Requires
Summation of Ca2+ Influx From Multiple Ca2+
Channels. J. Neurophysiol. 84: 1123-1135, 2000. Large-conductance
Ca2+ and voltage-dependent
K+ channels (BK channels) in many tissues require
high Ca2+ concentrations for activation and
therefore might be expected to be tightly coupled to
Ca2+ channels. However, in most cases, little is
known about the relative organization of the BK channels and the
Ca2+ channels involved in their activation. We
probed the nature of the organization of BK and
Ca2+ channels in rat chromaffin cells by
manipulating Ca2+ influx through
Ca2+ channels and by altering cellular
Ca2+ buffering using EGTA and
bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid
(BAPTA). The results were analyzed to determine the distance between
Ca2+ and BK channels that would be most
consistent with the experimental data. Most BK channels are close
enough to Ca2+ channels to be resistant to the
buffering action of millimolar of EGTA, but are far enough to be
inhibited by BAPTA. Analysis of the EGTA/BAPTA results suggests that BK
channels are at a distance of 50 to 160 nm from
Ca2+ channels. A model that assumes random
distribution of Ca2+ and BK channels fails to
account for the observed
[Ca2+]i detected by BK
channels, suggesting that a specific mechanism may exist to mediate the
functional coupling between these channels. Importantly, the effects of
EGTA and BAPTA cannot be explained by assuming a one-to-one coupling
between Ca2+ and BK channels. Rather,
Ca2+ influx through a number of
Ca2+ channels appears to act in concert to
regulate the behavior of any individual BK channel. Thus differences in
BK channel open probabilities may be explained by differences in the
extent of Ca2+ domain overlap at the sites of
individual BK channels.
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