Ryanodine-sensitive calcium stores involved in neurotransmitter release from sympathetic nerve terminals of the guinea-pig.
1. Intracellular and focal extracellular recording techniques were used to study neurotransmitter release mechanisms in postganglionic sympathetic nerve terminals in the guinea-pig isolated vas deferens. 2. High concentrations of the selective N-type calcium channel blocker omega-conotoxin GVIA abolished the release of the neurotransmitter ATP evoked by trains of low-frequency stimuli. However, in the presence of high concentrations of the blocker, a 'residual release' persisted at higher frequencies. 3. Residual release was dependent on calcium entry through a pharmacologically distinct voltage-dependent calcium channel. 4. Residual release was inhibited by ryanodine in a use- and time-dependent manner and this inhibitory effect was potentiated by caffeine. The inhibitory effect of ryanodine on residual release was reversed by 4-aminopyridine. 5. These findings indicate that calcium-induced calcium released from intraneuronal stores plays an important role in action potential-evoked neurotransmitter release mechanisms in postganglionic sympathetic nerve terminals.
Smith
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University Department of Pharmacology, Oxford, UK.
Cunnane
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TC
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D006168:Guinea Pigs; D008297:Male; D008978:Mollusk Venoms / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology*; D013564:Sympathetic Nervous System / Q000378:metabolism*; D014649:Vas Deferens / Q000294:innervation; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D008978:Mollusk Venoms; D018377:Neurotransmitter Agents; D010455:Peptides; D012433:Ryanodine; D000255:Adenosine Triphosphate; D020866:omega-Conotoxin GVIA; D002118:Calcium