Calcium channel subtypes differ at two types of cholinergic synapse in lumbar sympathetic neurones of guinea-pigs.
1. The involvement of different presynaptic Ca2+ channels in transmission at 'weak' (subthreshold) and 'strong' (suprathreshold) synapses was investigated in guinea-pig paravertebral ganglia isolated in vitro. Selective Ca2+ channel antagonists were used to block excitatory synaptic currents evoked by stimulating single preganglionic axons. 2. The N-type Ca2+ channel blocker, omega-conotoxin GVIA (100 nM), reduced peak synaptic conductance by similar amounts at weak synapses (by 39 +/- 6 %) and strong synapses (34 +/- 6 %). 3. The P-type Ca2+ channel blocker, omega-agatoxin IVA (40 nM), significantly reduced transmitter release at weak synapses (by 42 +/- 6 %) but had only a small effect at strong synapses (reduced by 6 +/- 2 %). 4. Blockers of Q-, L- or T-type Ca2+ channels had no significant effects on peak synaptic conductance at either type of synapse. 5. We conclude that the two functionally distinct types of preganglionic terminal in sympathetic ganglia which synapse on the same neurone differ in their expression of particular types of voltage-dependent Ca2+ channels. Both types utilize N-type channels and channels resistant to blockade by specific antagonists, but Ca2+ entry through P-type channels makes a substantial contribution to acetylcholine release only at weak synapses.
Ireland
D R
DR
Prince of Wales Medical Research Institute, Randwick, NSW 2031, Australia.
Davies
P J
PJ
McLachlan
E M
EM
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000032:analysis* / Q000502:physiology; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D020747:Calcium Channels, T-Type; D002799:Cholinergic Fibers / Q000737:chemistry*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D005728:Ganglia, Sympathetic / Q000737:chemistry* / Q000166:cytology; D005730:Ganglionic Blockers / Q000494:pharmacology; D006168:Guinea Pigs; D018738:Hexamethonium / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008161:Lumbosacral Region / Q000294:innervation; D008297:Male; D010455:Peptides / Q000494:pharmacology; D011073:Polyamines / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology; D013569:Synapses / Q000737:chemistry* / Q000187:drug effects; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D002104:Cadmium; D002118:Calcium; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D020747:Calcium Channels, T-Type; D005730:Ganglionic Blockers; D018738:Hexamethonium; D010455:Peptides; D011073:Polyamines; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; C071920:FTX, spider toxin