Nitrendipine block of calcium channel currents in vascular smooth muscle and adrenal glomerulosa cells

Nitrendipine block of calcium channel currents has been characterized using patch clamp recording from bovine adrenal glomerulosa cells and aortic vascular smooth muscle cell lines A7r5 and A10. Each preparation contains two distinct populations of voltage-dependent calcium channels. The slowly inactivating (L) channel in each preparation activates with strong depolarizations, deactivates rapidly, and is more susceptible to nitrendipine block. L channels predominate in vascular smooth muscle and may underlie maintained calcium influx during high potassium induced contractures. The second channel type (T) activates with weak depolarizations from hyperpolarized potentials, inactivates rapidly, deactivates slowly, and is less susceptible to nitrendipine block. T channels carry much of the calcium channel current in glomerulosa cells and may mediate stimulus-secretion coupling in these cells.