Evidence that Angiotensin-II and Potassium Collaborate to Increase Cytosolic Calcium and Stimulate the Secretion of Aldosterone*

Abstract Angiotensin-II (All) and potassium (K+) as stimuli of aldosterone secretion enhance each other's stimulatory potential. In the present study we looked for evidence that All and K+ act through a common mechanism of signal transduction to affect secretion. Bovine adrenal glomerulosa cells were loaded with the calcium (Ca2+) probe aequorin to permit detection over prolonged time periods of the changes in cytosolic Ca2+ that occur in response to All and K+. Perfusion fractions were collected for simultaneous measurement of aldosterone production rates. All (10–7 M) produced an immediate and transient increase in Ca2+, followed by a Ca2+ plateau that remained above baseline for as long as All was present. An increase in K+ concentration (from 5 to 12 mM) produced a slow and eventually sustained increase in cytosolic Ca2+, which resembled the plateau produced by All. Nitrendipine (10–5 M) completely inhibited the secretory response to All and K+ (during 60-min incubations) and inhibited the typical K+-...