RESUMEN

The role of voltage-gated Ca2+ channels (VGCCs) in spontaneous miniature neurotransmitter release is incompletely understood. We found that stochastic opening of P/Q-, N- and R-type VGCCs accounts for ∼50% of all spontaneous glutamate release at rat cultured hippocampal synapses, and that R-type channels have a far greater role in spontaneous than in action potential-evoked exocytosis. VGCC-dependent miniature neurotransmitter release (minis) showed similar sensitivity to presynaptic Ca2+ chelation as evoked release, arguing for direct triggering of spontaneous release by transient spatially localized Ca(2+) domains. Experimentally constrained three-dimensional diffusion modeling of Ca2+ influx-exocytosis coupling was consistent with clustered distribution of VGCCs in the active zone of small hippocampal synapses and revealed that spontaneous VGCCs openings can account for the experimentally observed VGCC-dependent minis, although single channel openings triggered release with low probability. Uncorrelated stochastic VGCC opening is therefore a major trigger for spontaneous glutamate release, with differential roles for distinct channel subtypes.

Asunto(s)

Canales de Calcio/clasificación , Canales de Calcio/fisiología , Ácido Glutámico/metabolismo , Activación del Canal Iónico/fisiología , Neuronas/metabolismo , Animales , Animales Recién Nacidos , Calcio/metabolismo , Agonistas de los Canales de Calcio/farmacología , Bloqueadores de los Canales de Calcio , Células Cultivadas , Quelantes/farmacología , Ácido Egtácico/análogos & derivados , Ácido Egtácico/farmacología , Estimulación Eléctrica , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Hipocampo/citología , Activación del Canal Iónico/efectos de los fármacos , Modelos Biológicos , Neuronas/efectos de los fármacos , Técnicas de Placa-Clamp , Ratas , Ratas Sprague-Dawley , Procesos Estocásticos