omega-Agatoxin-IVA-sensitive calcium channels in bovine chromaffin cells.
A large component of the whole-cell currents through Ca2+ channels in bovine adrenomedullary chromaffin cells has been shown to be insensitive to both L-type and N-type Ca2+ channel blockers, suggesting the existence of a third type of Ca2+ channel. In the present paper, omega-agatoxin-IVA (AgTx), a selective blocker of P-type Ca2+ channels in mammalian neurons, has been used to investigate the presence of this subtype of Ca2+ channel in bovine chromaffin cells. Barium currents (IBa) through Ca2+ channels were recorded in whole-cell patch-clamped bovine chromaffin cells. IBa was blocked by AgTx in a dose-dependent and irreversible manner. At the maximal concentration used (1 microM), AgTx inhibited IBa by 49.5 +/- 3%. Such a blockade was also present when bovine chromaffin cells were pretreated with 10 microM furnidipine, a novel 1,4-dihydropyridine L-type channel blocker, and after treatment with 1 microM of the N-type channel blocker, omega-conotoxin GVIA (CgTx). A combination of these three types of Ca2+ channel blockers suppressed the macroscopic Ba2+ currents by 88%. We conclude that bovine chromaffin cells, in addition to N- and L-type Ca2+ channels, possess a P-like component in their whole-cell currents through the Ca2+ channels.
Albillos
A
A
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
García
A G
AG
Gandía
L
L
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001464:Barium / Q000378:metabolism; D001665:Binding Sites; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D002838:Chromaffin System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D013111:Spider Venoms / Q000494:pharmacology*; D020867:omega-Agatoxin IVA
D002121:Calcium Channel Blockers; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D001464:Barium