Localized L-type calcium channels control exocytosis in cat chromaffin cells

• Published in: Pflügers Archiv 1994-06, Vol.427 (3-4), p.348-354
• Main Authors: LOPEZ, M. G, ALBILLOS, A, DE LA FUENTE, M. T, BORGES, R, GANDIA, L, CARBONE, E, GARCIA, A. G, ARTALEJO, A. R
• Format: Article
• Language: English
• Subjects: Adrenal Medulla - cytology; Adrenal Medulla - drug effects; Adrenal Medulla - metabolism; Adrenals. Interrenals; Adrenomedullary hormones. Regulation; Animals; Biological and medical sciences; Calcium Channel Blockers - pharmacology; Calcium Channels - classification; Calcium Channels - drug effects; Calcium Channels - physiology; Catecholamines - metabolism; Cats; Cells, Cultured; Dihydropyridines - pharmacology; Exocytosis - physiology; Fundamental and applied biological sciences. Psychology; omega-Conotoxin GVIA; Peptides - pharmacology; Vertebrates: endocrinology
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/BF00374544

Depolarizing 1-s pulses to 0 mV from a holding potential of -70 mV, induced whole-cell currents through Ca2+ channels (ICa) in patch-clamped cat adrenal medulla chromaffin cells. The dihydropyridine (DHP) furnidipine (3 microM) reduced the peak current by 47% and the late current by 80%. omega-Conotoxin GVIA (CgTx, 1 microM) reduced the peak ICa by 42% and the late ICa by 55%. Pulses (10 s duration) with 70 mM K+/2.5 mM Ca2+ solution (70 K+/2.5 Ca2+), applied to single fura-2-loaded cat chromaffin cells increased the cytosolic Ca2+ concentration ([Ca2+]i) from 0.1 to 2.21 microM; this increase was reduced by 43.7% by furnidipine and by 42.5% by CgTx. In the perfused cat adrenal gland, secretion evoked by 10-s pulses of 70 K+/2.5 Ca2+ was reduced by 25% by CgTx and by 96% by furnidipine. Similar results were obtained when secretion from superfused isolated cat adrenal chromaffin cells was studied and when using a tenfold lower [Ca2+]o. The results are compatible with the existence of DHP-sensitive (L-type) as well as CgTx-sensitive (N-type) voltage-dependent Ca2+ channels in cat chromaffin cells. It seems, however, that though extracellular Ca2+ entry through both channel types leads to similar increments of averaged [Ca2+]i, the control of catecholamine release is dominated only by Ca2+ entering through L-type Ca2+ channels. This supports the idea of a preferential segregation of L-type Ca2+ channels to localized "hot spots" in the plasmalemma of chromaffin cells where exocytosis occurs.