Dual and opposing roles of presynaptic Ca2+ influx for spontaneous GABA release from rat medial preoptic nerve terminals.
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.
Druzin
Michael
M
Department of Integrative Medical Biology, Section for Physiology, Umeå University, S-901 87 Umeå, Sweden.
Haage
David
D
Malinina
Evgenya
E
Johansson
Staffan
S
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009411:Nerve Endings / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D009553:Nimodipine / Q000494:pharmacology; D009900:Optic Nerve / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017661:Receptors, Presynaptic / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D020960:omega-Conotoxins / Q000494:pharmacology
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D017661:Receptors, Presynaptic; D020960:omega-Conotoxins; D005680:gamma-Aminobutyric Acid; D009553:Nimodipine; D002118:Calcium