Ca channels in adrenal glomerulosa cells: K+ and angiotensin II increase T-type Ca channel current

Abstract

Ca channel currents were studied in freshly dispersed bovine adrenal glomerulosa cells to better understand the control of aldosterone secretion by extracellular K concentration (K(o)) and angiotensin II (AII). The whole-cell variation of the patch voltage clamp technique was used. Two types of Ca channels were found. One type is similar to the 'T-type' Ca channels found in many excitable cells. These channels deactivate slowly (τ ~7 ms at -75 mV) and inactivate rapidly during strong depolarizations. The second channel type activates and inactivates at more positive potentials than the T-type Ca channels and deactivates rapidly. These channels are similar to the 'L-type' Ca channels found in muscle and nerve. Our studies provide three reasons for concluding that T-type Ca channels have an important role in mediating stimulus-secretion coupling in response to high K+ or AII: (i) aldosterone secretion and steady-state current through T-type Ca channels are biphasic functions of K(o) and both increase in parallel for K(o) = 2-10 mM; (ii) nitrendipine blocks the T-type Ca channels and the stimulation of aldosterone secretion by high K+ or AII with similar potency; (iii) AII increases Ca entry through the T-type Ca channels.