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The Journal of Neurophysiology Vol. 81 No. 5 May 1999, pp. 2267-2278
Copyright ©1999 by the American Physiological Society
Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
Prakriya, Murali and
Christopher J. Lingle.
BK Channel Activation by Brief Depolarizations Requires
Ca2+ Influx Through L- and Q-Type Ca2+ Channels
in Rat Chromaffin Cells. J. Neurophysiol. 81: 2267-2278, 1999.
BK channel activation by brief depolarizations requires
Ca2+ influx through L- and Q-type Ca2+ channels
in rat chromaffin cells. Ca2+- and
voltage-dependent BK-type K+ channels contribute to action
potential repolarization in rat adrenal chromaffin cells. Here we
characterize the Ca2+ currents expressed in these cells and
identify the Ca2+ channel subtypes that gate the activation
of BK channels during Ca2+ influx. Selective
Ca2+ channel antagonists indicate the presence of at least
four types of high-voltage-gated Ca2+ channels: L-, N-, P,
and Q type. Mean amplitudes of the L-, N-, P-, and Q-type
Ca2+ currents were 33, 21, 12, and 24% of the total
Ca2+ current, respectively. Five-millisecond
Ca2+ influx steps to 0 mV were employed to assay the
contribution of Ca2+ influx through these Ca2+
channels to the activation of BK current. Blockade of L-type Ca2+ channels by 5 µM nifedipine or Q-type
Ca2+ channels by 2 µM Aga IVA reduced BK current
activation by 77 and 42%, respectively. In contrast, blockade of
N-type Ca2+ channels by brief applications of 1-2 µM
CnTC MVIIC or P-type Ca2+ channels by 50-100 nM Aga IVA
reduced BK current activation by only 11 and 12%, respectively.
Selective blockade of L- and Q-type Ca2+ channels also
eliminated activation of BK current during action potentials, whereas
almost no effects were seen by the selective blockade of N- or P-type
Ca2+ channels. Finally, the L-type Ca2+ channel
agonist Bay K 8644 promoted activation of BK current by brief
Ca2+ influx steps by more than twofold. These data show
that, despite the presence of at least four types of Ca2+
channels in rat chromaffin cells, BK channel activation in rat chromaffin cells is predominantly coupled to Ca2+ influx
through L- and Q-type Ca2+ channels.
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