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 a t 'weak' (subthreshold) and 'strong' (suprathreshold) synapses was investig ated in guinea-pig paravertebral ganglia isolated in vitro. Selective Ca2channel 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), significant ly 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 te rminal in sympathetic ganglia which synapse on the same neurone differ in t heir expression of particular types of voltage-dependent Ca2+ channels. Bot h types utilize N-type channels and channels resistant to blockade by speci fic antagonists, but Ca2+ entry through P-type channels makes a substantial contribution to acetylcholine release only at weak synapses.