Calcium channel types with distinct presynaptic localization couple differentially to transmitter release in single calyx-type synapses.
We studied how Ca2+ influx through different subtypes of Ca2+ channels couples to release at a calyx-type terminal in the rat medial nucleus of the trapezoid body by simultaneously measuring the presynaptic Ca2+ influx evoked by a single action potential and the EPSC. Application of subtype-specific toxins showed that Ca2+ channels of the P/Q-, N-, and R-type controlled glutamate release at a single terminal. The Ca2+ influx through the P/Q-type channels triggered release more effectively than Ca2+ influx through N- or R-type channels. We investigated mechanisms that contributed to these differences in effectiveness. Electrophysiological experiments suggested that individual release sites were controlled by all three subtypes of Ca2+ channels. Immunocytochemical staining indicated, however, that a substantial fraction of N- and R-type channels was located distant from release sites. Although these distant channels contributed to the Ca2+ influx into the terminal, they may not contribute to release. Taken together, the results suggest that the Ca2+ influx into the calyx via N- and R-type channels triggers release less effectively than that via P/Q-type because a substantial fraction of the N- and R-type channels in the calyx is localized distant from release sites.
Wu
L G
LG
Abteilung Zellphysiologie, Max-Planck-Institut für medizinische Forschung, D-69120 Heidelberg, Germany.
Westenbroek
R E
RE
Borst
J G
JG
Catterall
W A
WA
Sakmann
B
B
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001933:Brain Stem / Q000378:metabolism / Q000648:ultrastructure; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D018377:Neurotransmitter Agents / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D050857:Synaptotagmins
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002614:Chelating Agents; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D050857:Synaptotagmins; D004533:Egtazic Acid