Different calcium channels mediate transmitter release evoked by transient or sustained depolarization at mammalian sympathetic ganglia.
We have compared the effect of calcium channel blockers on the potassium-evoked release of tritium-labeled acetylcholine and on preganglionic spike-evoked synaptic transmission in the rat superior cervical ganglion. Transmitter release at the nerve terminals is mediated by the influx of calcium through voltage-gated calcium channels. While four types of voltage-gated calcium channels (T, L, N and P) have been identified in neurons, it is not clear which may actually be involved in excitation-secretion coupling. Release of tritiated acetylcholine evoked by sustained depolarization in high (40 mM) extracellular potassium decreased markedly in the absence of calcium or the presence of cadmium. High potassium-evoked release was substantially inhibited by the P-type channel blockers, purified from funnel-web spider toxin, and omega-agatoxin-IVA, and by the N-type channel blocker omega-conotoxin-GVIA, but was unaffected by the L-type channel blocker nitrendipine. In contrast, postganglionic compound action potentials synaptically triggered by preganglionic stimulation were strongly blocked by funnel-web spider toxin and slightly blocked by a high concentration of omega-agatoxin-IVA, but were unaffected by either omega-conotoxin-GVIA, nitrendipine or a low concentration of omega-agatoxin-IVA. Thus, at the superior cervical ganglion, funnel-web spider toxin-sensitive calcium channels play a dominant role in transmitter release evoked by transient, spike-mediated depolarization, but other types of voltage-gated calcium channels in addition to the funnel-web spider toxin-sensitive channel mediate the transmitter release that is evoked by sustained high potassium depolarization.
Gonzalez Burgos
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GR
Departamento de Fisiología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay, Argentina.
Biali
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FI
Cherksey
B D
BD
Sugimori
M
M
Llinás
R R
RR
Uchitel
O D
OD
D000109:Acetylcholine / Q000378:metabolism*; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005728:Ganglia, Sympathetic / Q000502:physiology*; D011073:Polyamines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013095:Spermidine / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; C071920:FTX, spider toxin; D011073:Polyamines; D001120:Arginine; D000109:Acetylcholine; D013095:Spermidine