Voltage-operated Ca(2+) channels involved in K(+)-evoked release of vasoactive intestinal polypeptide from the rat hypothalamus.
Rat brain hypothalami were exposed to various depolarizing stimuli and vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) release was measured by means of a radioimmunoassay (RIA) procedure. Under conditions of noradrenergic blockade, exposure to high K(+) (40-100 mM) produced dose-dependent increases in the VIP-LI release in a Ca(2+)-dependent manner. Exposure to veratridine (3-100 microM) also induced concentration-dependent increases in VIP-LI release, an effect that was Ca(2+)-dependent and tetrodotoxin (TTX)-sensitive. Specific ligands for the L, N, and P/Q-type voltage-operated Ca(2+) channels (VOCCs) were used to determine which channel subtypes were involved in the K(+)-evoked VIP-LI release. The L-type VOCC ligand, nifedipine (10 microM), had no effect on release. In contrast, the N-type VOCC blocker, omega-conotoxin GVIA (omega-CgTx GVIA) (0.1-100 nM), markedly reduced the K(+)-evoked response, with maximal inhibition of approximately 60+/-8%. omega-Agatoxin IVA (omega-Aga IVA) (1-50 nM), which binds P-type and, at high doses, also Q-type VOCCs, produced dose-dependent inhibition of up to 25+/-3%, while the maximal inhibition observed with the non-selective VOCCs ligand, omega-conotoxin MVIIC (omega-CmTx MVIIC) (1 nM-3 microM), amounted to 85+/-8%. These findings indicate that N and P-type Ca(2+) channels play predominant roles in the high K(+)-evoked release of VIP-LI from the rat hypothalamus.
Martire
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Institute of Pharmacology, Catholic University of Sacred Heart, School of Medicine, Largo F. Vito, 1-00168, Rome, Italy. mmartire@rm.unicatt.it
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D018663:Adrenergic Agents / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D017077:Culture Media, Conditioned / Q000032:analysis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006145:Guanethidine / Q000494:pharmacology; D007031:Hypothalamus / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013268:Stimulation, Chemical; D013779:Tetrodotoxin / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D018663:Adrenergic Agents; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D017077:Culture Media, Conditioned; D007476:Ionophores; D015016:Yohimbine; D014660:Vasoactive Intestinal Peptide; D013779:Tetrodotoxin; D014701:Veratridine; D011188:Potassium; D002118:Calcium; D006145:Guanethidine