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First published online on May 17, 2002.
 Copyright © 2002 by The Physiological Society
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Received December 18, 2001
Accepted after revision April 23, 2002

Dual and opposing roles of presynaptic Ca2+ influx for spontaneous GABA release from rat medial preoptic nerve terminals

Michael Druzin1, David Haage2, Evgenya Malinina1, and S. Johansson2*

1 Department of Integrative Medical Biology, Section for Physiology, Umea University, S-901 87 Umea, Sweden and Laboratory of Ionic Channels of Cell Membranes, Institute of Cytology, Russian Academy of Sciences, St Petersburg 194064, Russia
2 Department of Integrative Medical Biology, Section for Physiology, Umea University, S-901 87 Umea, Sweden

* To whom correspondence should be addressed. E-mail: staffan.johansson{at}physiol.umu.se.

Calcium influx into the presynaptic nerve terminal is well established as a trigger signal for transmitter release by exocytosis. By studying dissociated preoptic neurons with functional adhering nerve terminals, we here show that presynaptic Ca2+ influx plays dual and opposing roles in the control of spontaneous transmitter release. Thus, application of various Ca2+ channel blockers paradoxically increased the frequency of spontaneous (miniature) inhibitory GABA-mediated postsynaptic currents (mIPSCs). Similar effects on mIPSC frequency were recorded upon washout of Cd2+ or EGTA from the external solution. The results are explained by a model with parallel Ca2+ influx through channels coupled to the exocytotic machinery and through channels coupled to Ca2+-activated K+ channels at a distance from the release site.




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