ω-Conotoxins block neurotransmission in the rat vas deferens by binding to different presynaptic sites on the N-type Ca2+ channel

• Published in: European journal of pharmacology 1997-02, Vol.321 (2), p.217-223
• Main Authors: HIRATA, H, ALBILLOS, A, FERNANDEZ, F, MEDRANO, J, JURKIEWICZ, A, GARCIA, A. G
• Format: Article
• Language: English
• Subjects: Animals; Binding Sites; Biological and medical sciences; Calcium - metabolism; Calcium Channel Blockers - metabolism; Calcium Channel Blockers - toxicity; Calcium Channels - drug effects; Calcium Channels - metabolism; Cell membranes. Ionic channels. Membrane pores; Cell structures and functions; Electric Stimulation; Fundamental and applied biological sciences. Psychology; Male; Molecular and cellular biology; Muscle Contraction - drug effects; Neurotoxins - metabolism; Neurotoxins - toxicity; omega-Agatoxin IVA; omega-Conotoxin GVIA; omega-Conotoxins; Peptides - metabolism; Peptides - toxicity; Peripheral nervous system. Autonomic nervous system. Neuromuscular transmission. Ganglionic transmission. Electric organ; Rats; Rats, Wistar; Spider Venoms - metabolism; Spider Venoms - toxicity; Synaptic Transmission - drug effects; Vas Deferens - drug effects; Vas Deferens - innervation; Vas Deferens - metabolism; Vertebrates: nervous system and sense organs
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/S0014-2999(96)00951-X

Electrically-induced twitch responses of the prostatic segment of vas deferens (0.1 Hz, 65 V, 1 ms) are mainly due to the transient presynaptic release of ATP, which acts postsynaptically on non-adrenergic receptors to contract smooth muscle cells. These responses were fully blocked by nanomolar concentrations of the omega-conotoxins GVIA, MVIIA, and MVIIC, most likely by inhibiting Ca2+ entry through presynaptic N-type Ca2+ channels controlling the release of ATP. Repeated washout of the toxins allowed the recovery of contractions, except for omega-conotoxin GVIA, whose inhibitory effects remained unchanged for at least 60 min. In addition, micromolar concentrations of omega-conotoxin MVIIC were unable to protect against the irreversible inhibition of twitch contractions induced by nanomolar concentrations of omega-conotoxin GVIA. At low extracellular Ca2+ concentrations (1.5 mM), 20 nM of omega-conotoxin GVIA or MVIIA inhibited completely the twitch contractions in about 10 min. In 5 mM Ca2+ the blockade of twitch contractions after 10 min was 70% for both toxins. In 1.5 mM Ca2+ omega-conotoxin MVIIC (1 microM) inhibited completely the twitch contraction after 10 min. In 5 mM Ca2+ blockade developed very slowly and was very poor after 30 min, omega-conotoxin MVIIC depressed the response by only 20%. These results are compatible with the idea that the three omega-conotoxins block the purinergic neurotransmission of the vas deferens by acting on presynaptic N-type voltage-dependent Ca2+ channels. However, omega-conotoxin MVIIC seems to bind to sites different from those recognised by omega-conotoxin GVIA and MVIIA, which are markedly differentiated by their Ca2+ requirements for binding to their receptors.