Calcium channel subtypes in porcine adrenal chromaffin cells |
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Authors: | Naoki Kitamura Toshio Ohta Shigeo Ito Y Nakazato |
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Institution: | (1) Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, North 18th West 9th, Sapporo 060, Japan, JP |
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Abstract: | The effects of nifedipine, ω-conotoxin GVIA (ω-CgTx) and ω-agatoxin IVA (ω-AgTx) on Ca2+ currents, a 60-mM-K+-induced increase in intracellular Ca2+ concentration (Ca2+]i) and catecholamine secretion were examined to clarify the subtypes of Ca2+ channels in cultured adrenal chromaffin cells from the pig. Nifedipine, ω-CgTx, and ω-AgTx inhibited Ca2+ currents in a dose-dependent manner, suggesting the presence of L-, N- and P-type Ca2+ channels. The maximal doses of nifedipine (10 μM), ω-CgTx (1 μM), and ω-AgTx (0.1 μM) inhibited Ca2+ currents to 85%, 22%, and 94% of control currents, respectively. The inhibitory effects of these three blockers were observed
in the same cell, indicating that at least three subtypes of Ca2+ channels are present in porcine chromaffin cells. The increase in Ca2+]i and catecholamine secretion induced by 60 mM K+ were inhibited equally by nifedipine (10 μM) and ω-CgTx (1 μM), but not by ω-AgTx (0.1 μM). These results suggest that L-,
N- and P-type Ca2+ channels are present in porcine adrenal chromaffin cells, and that the major pathways of Ca2+ entry evoked by a high concentration of K+ are L- and N-type Ca2+ channels.
Received: 6 September 1996 / Received after revision: 3 February 1997 / Accepted: 18 February 1997 |
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Keywords: | Adrenal chromaffin cell Ca2+ current Ca2+ channel Nifedipine ω -Conotoxin GVIA ω -Agatoxin IVA |
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