Evidence suggesting that the angiotensin II-sensitive intracellular Ca2+ pool is reloaded from the external space in adrenal glomerulosa cells

Adrenal glomerulosa cells prelabeled with Ca-45(2+) and perifused for 10 mi n with 10 nM angiotensin II (AII) in a dynamic perifusion system show a bip hasic response with an initial transient increase in Ca-45(2+) efflux, foll owed by a sustained phase of increased Ca-45(2+) efflux. When labeled adren al golmerulosa cells were treated with 10 nM AII for three consecutive peri ods of 5 min, the transient increase in Ca-45(2+) efflux was observed only in the first period. However, when Ca-40(2+) was measured in the perifusate using a Ca2+-sensitive electrode coupled to the perifusion system, a trans ient increase in Ca-40(2+) efflux was observed in each period of AII treatm ent. Exposing the cells to AII for 1 min, the amount of Ca-40(2+) effluxed out of the cells was 58.3 +/- 8.4 nmol/10(8) cells. In contrast, when the c ells were exposed to an increase in the external potassium (K+) concentrati on of 4 to 12 mM during 1 min of perifusion, the amount of Ca-40(2+) efflux ed was 16 +/- 5 nmol/10(8) cells. These results indicate that AII induces a n increase in the Ca2+ concentration in a local domain outside of the plasm a membrane. This Ca2+ comes from AII-induced intracellular Ca2+ depletion a nd may play a role in refilling intracellular Ca2+ stores. (C) 1999 Elsevie r Science Inc. All rights reserved.