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J. Gen. Physiol.,
Volume 111, Number 2, February 1, 1998 257-269
From the Department of Pharmacological and Physiological Sciences, The University of Chicago, Chicago, Illinois 60637
The functional effect of activating Ca2+-permeable neuronal nicotinic acetylcholine receptors
(nAChRs) on vesicle secretion was studied in PC12 cells. Single cells were patch-clamped in the whole-cell configuration and stimulated with either brief pulses of nicotine to activate the Ca2+-permeable nAChRs or with voltage
steps to activate voltage-dependent Ca2+ channels. Membrane capacitance was used as a measure of vesicle secretion. Activation of nAChRs by nicotine application to cells voltage clamped at
80 mV evoked secretion. This secretion was completely abolished by nicotinic antagonists. When the cells were voltage clamped at +20 mV in the
presence of Cd2+ to block voltage-activated Ca2+ channels, nicotine elicited a small amount of secretion. Most interestingly, when the nAChRs were activated coincidentally with voltage-dependent Ca2+ channels, secretion was
augmented approximately twofold over the secretion elicited with voltage-dependent Ca2+ channels alone. Our
data suggest that Ca2+ influx via nAChRs affects Ca2+-dependent cellular functions, including vesicle secretion. In addition to the secretion evoked by nAChR activation at hyperpolarized potentials, we demonstrate that even at
depolarized potentials, nAChRs provide an important Ca2+ entry pathway underlying Ca2+-dependent cellular
processes such as exocytosis.
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