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Calcium channel subtypes in porcine adrenal chromaffin cells
1Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, North 18th West 9th, Sapporo 060, Japan.
Abstract:
The effects of nifedipine, omega-conotoxin GVIA (omega-CgTx) and omega-agatoxin IVA (omega-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, omega-CgTx, and omega-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 microM), omega-CgTx (1 microM), and omega-AgTx (0.1 microM) 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 microM) and omega-CgTx (1 microM), but not by omega-AgTx (0.1 microM). 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.
Insights
This study identified L-, N-, and P-type calcium channels in pig adrenal chromaffin cells using specific blockers. L- and N-type channels are primarily responsible for high potassium-induced calcium influx and catecholamine secretion.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- Adrenal chromaffin cells are crucial for catecholamine release.
- Calcium (Ca2+) channels play a vital role in cellular signaling and secretion.
- Understanding Ca2+ channel subtypes is essential for elucidating cellular mechanisms.
Purpose of the Study:
- To identify and characterize the subtypes of Ca2+ channels present in cultured porcine adrenal chromaffin cells.
- To determine the contribution of different Ca2+ channel subtypes to Ca2+ influx and catecholamine secretion.
Main Methods:
- Utilized specific Ca2+ channel blockers: nifedipine (L-type), omega-conotoxin GVIA (omega-CgTx, N-type), and omega-agatoxin IVA (omega-AgTx, P-type).
- Measured effects on Ca2+ currents, high potassium (60 mM K+)-induced intracellular Ca2+ concentration ([Ca2+]i) increase, and catecholamine secretion.
- Administered blockers to the same cells to assess differential inhibition.
Main Results:
- Nifedipine, omega-CgTx, and omega-AgTx dose-dependently inhibited Ca2+ currents, indicating the presence of L-, N-, and P-type channels.
- Maximal inhibition showed significant effects: nifedipine (85%), omega-CgTx (22%), and omega-AgTx (94%).
- High K+-induced [Ca2+]i increase and catecholamine secretion were significantly inhibited by nifedipine and omega-CgTx, but not by omega-AgTx.
Conclusions:
- Porcine adrenal chromaffin cells express L-, N-, and P-type Ca2+ channels.
- L- and N-type Ca2+ channels are the primary mediators of Ca2+ entry and subsequent catecholamine release stimulated by high extracellular K+ concentrations.