title: Multiple calcium channels control neurotransmitter release from rat postganglionic sympathetic nerve terminals.
abstract: 1. Intracellular recording techniques were used to study neurotransmitter release mechanisms in postganglionic sympathetic nerve terminals of the rat isolated anococcygeus muscle. 2. Low concentrations of the N-type calcium channel blocker omega-conotoxin GVIA (omega-CgTX GVIA) irreversibly abolished excitatory junction potentials (EJPs) evoked by trains of < or = five stimuli at 10 Hz. When the frequency of stimulation was increased (10-50 Hz) trains of stimuli evoked EJPs even in the presence of 1 microM omega-CgTX GVIA. We have termed this omega-CgTX GVIA-resistant release 'residual release'. EJP amplitude in the presence of omega-CgTX GVIA depended on both the frequency and number of stimuli in a train. 3. Residual release was inhibited by the P-type calcium channel blocker omega-agatoxin IVA (100 nM). However, even in the presence of both toxins, longer trains of stimuli could still evoke neurotransmitter release. 4. Residual release was abolished by omega-conotoxin MVIIC and by the non-specific calcium channel antagonist omega-grammotoxin SIA. Therefore, it would appear that a heterogeneous population of calcium channels is involved in mediating neurotransmitter release from these sympathetic nerve terminals.
authors.affiliation: University Department of Pharmacology, Oxford, UK.
authors.forename: A B
authors.initials: AB
authors.lastname: Smith
authors.forename: T C
authors.initials: TC
authors.lastname: Cunnane
mesh_terms: D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D005071:Evoked Potentials / Q000187:drug effects; D008297:Male; D008978:Mollusk Venoms / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; D020960:omega-Conotoxins
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D018377:Neurotransmitter Agents; D010455:Peptides; D010456:Peptides, Cyclic; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020960:omega-Conotoxins; C082807:omega-grammotoxin SIA; C075851:omega-conotoxin-MVIIC; D020866:omega-Conotoxin GVIA