Spontaneous action potentials initiate rhythmic intercellular calcium waves in immortalized hypothalamic (GT1-1) neurons.
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 microM 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.
Department of Neurology, UCLA School of Medicine, Los Angeles, California 90095-1769, USA.
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Costantin
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Charles
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002461:Cell Line, Transformed; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism; D007031:Hypothalamus / Q000502:physiology*; D051379:Mice; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013997:Time Factors; D014741:Video Recording
D015220:Calcium Channels; D007987:Gonadotropin-Releasing Hormone; D002118:Calcium