EFFECTS OF OMEGA-CONOTOXIN GVIA ON ELECTRICAL-FIELD STIMULATION-INDUCED AND AGONIST-INDUCED CHANGES IN CYTOSOLIC CA2+ AND TENSION IN ISOLATED RAT ANOCOCCYGEUS MUSCLE

1 It has been reported that co-conotoxin GVIA (omega-CgTx) blocks L- and N-type voltage-sensitive Ca2+ channels (VSCCs) in neurones and inhibits neurotransmitter release in various tissues. The present study investigates the effects of omega-CgTx on electrical field stimulation (EFS)- and agonist-induced changes in free cytosolic Ca2+ ([Ca2+](cyt)) levels and tension in isolated fura-2 loaded rat anococcygeus muscle. 2 EFS produced frequency-dependent increases in [Ca+](cyt) levels and contractions. Phentolamine (1 mu M) and omega-CgTx (0.1 mu M) significantly inhibited EFS-induced responses and shifted the frequency-response curves to the right. 3 alpha-adrenoceptor agonists (noradrenaline and clonidine) and carbachol (in the presence of phentolamine) produced concentration-dependent increases in [Ca2+](cyt) levels and contractions. Though omega-CgTx (0.1 mu M) significantly inhibited the increases in [Ca2+](cyt) levels induced by low doses of noradrenaline, the overall concentration-response curves of [Ca2+](cyt) and contractions for noradrenaline, clonidine, and carbachol were not affected by omega-CgTx.