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The Journal of Neurophysiology Vol. 82 No. 1 July 1999, pp. 429-435
Copyright ©1999 by the American Physiological Society
Department of Neurology, UCLA School of Medicine, Los Angeles, California 90095-1769
Costantin, James L. and
Andrew C. Charles.
Spontaneous Action Potentials Initiate Rhythmic Intercellular
Calcium Waves in Immortalized Hypothalamic (GT1-1) Neurons. J. Neurophysiol. 82: 429-435, 1999.
GT1-1
cells exhibit spontaneous action potentials and transient increases in
intracellular calcium concentration ([Ca2+]i)
that occur in individual cells and as spatially propagated intercellular Ca2+ waves. In this study, simultaneous
cell-attached patch-clamp recording of action currents (indicative of
action potentials) and fluorescence imaging of
[Ca2+]i revealed that Ca2+
transients in GT1-1 cells were preceded by a single action current or
a burst of action currents. Action currents preceded Ca2+
transients in a similar pattern regardless of whether the
Ca2+ transients were limited to the individual cell or
occurred as part of an intercellular Ca2+ wave. Both the
action currents and Ca2+ transients were abolished by 1 µM tetrodotoxin. Removal of extracellular Ca2+ abolished
all spontaneous Ca2+ transients without inhibiting the
firing of action currents. Nimodipine, which blocks L-type
Ca2+ currents in GT1-1 cells, also abolished all
spontaneous Ca2+ signaling. Delivery of small voltage steps
to the patch pipette in the cell-attached configuration elicited action
currents the latency to firing of which decreased with increasing
amplitude of the voltage step. These results indicate that spontaneous
intercellular Ca2+ waves are generated by a propagated
depolarization, the firing of action potentials in individual cells,
and the resulting influx of Ca2+ through L-type
Ca2+ channels. These patterns of spontaneous activity may
be important in driving the pulsatile release of GnRH from networks of cells.
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