Inhibition of transmitter release from sympathetic nerve endings by omega-conotoxin.
1. The effects of the calcium channel blocker, omega-conotoxin, on sympathetic neuroeffector function in the guinea-pig vas deferens have been investigated using a combination of mechanical and electrophysiological recording techniques. 2. Biphasic contractions evoked by electrical field stimulation were irreversibly abolished by omega-conotoxin (10-100 nmol/L). 3. Electrically evoked excitatory junction potentials and currents were irreversibly blocked by omega-conotoxin (10-100 nmol/L). Spontaneous excitatory junction potentials and currents were unaffected by this treatment. 4. omega-Conotoxin did not block impulse propagation in the nerve terminals. However, in three of four experiments omega-conotoxin caused a decrease in the size of the nerve terminal impulse. 5. These findings support the suggestion the omega-conotoxin acts prejunctionally to inhibit sympathetic neuroeffector by interfering with depolarization-secretion coupling.
Brock
J A
JA
University Department of Pharmacology, Oxford, United Kingdom.
Cunnane
T C
TC
Evans
R J
RJ
Ziogas
J
J
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004594:Electrophysiology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008978:Mollusk Venoms / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000378:metabolism*; D013564:Sympathetic Nervous System / Q000378:metabolism*; D014649:Vas Deferens / Q000187:drug effects / Q000378:metabolism; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D008978:Mollusk Venoms; D018377:Neurotransmitter Agents; D020866:omega-Conotoxin GVIA