Q- and L-type Ca2+ channels dominate the control of secretion in bovine chromaffin cells.
Potassium-stimulated catecholamine release from superfused bovine adrenal chromaffin cells (70 mM K+ in the presence of 2 mM Ca2+ for 10 s, applied at 5-min intervals) was inhibited by the dihydropyridine furnidipine (3 microM) by 50%. omega-Conotoxin MVIIC (CTx-MVIIC, 3 microM) also reduced the secretory response by about half. Combined CTx-MVIIC plus furnidipine blocked 100% catecholamine release. 45Ca2+ uptake and cytosolic Ca2+ concentrations ([Ca2+]i) in K(+)-depolarized cells were partially blocked by furnidipine or CTx-MVIIC, and completely inhibited by both agents. The whole cell current through Ca2+ channels carried by Ba2+ (IBa) was partially blocked by CTx-MVIIC. Although omega-conotoxin GVIA (CTx-GVIA, 1 microM) and omega-agatoxin IVA (Aga-IVA, 0.2 microM) partially inhibited 45Ca2+ entry, IBa and the increase in [Ca2+]i, the combination of both toxins did not affect the K(+)-evoked secretory response. The results are compatible with the presence in bovine chromaffin cells of a Q-like Ca2+ channel which has a prominent role in controlling exocytosis. They also suggest that Q- and L-type Ca2+ channels, but not N- or P-types are localized near exocytotic active sites in the plasmalemma.
López
M G
MG
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Villarroya
M
M
Lara
B
B
Martínez Sierra
R
R
Albillos
A
A
García
A G
AG
Gandía
L
L
D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D008954:Models, Biological; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002395:Catecholamines; D009467:Neuromuscular Depolarizing Agents; D001464:Barium; D011188:Potassium; D002118:Calcium