External calcium is required for activation of phospholipase C by angiotensin II in adrenal glomerulosa cells.
Previous studies have shown that external calcium (Ca2+) is required for the effects of angiotensin II (AII) on aldosterone secretion in adrenal glomerulosa zone. Using bovine adrenal glomerulosa cells prepared by collagenase dispersion, we examined whether external Ca2+ is required for the activation of phospholipase C by AII. Adrenal glomerulosa cells were exposed to Ca-EGTA buffered media to provide accurate estimates of external free Ca2+ concentrations. Phospholipase C activation was evaluated by measurement of inositol phosphates production. At 0.1 microM Ca2+ and less, sustained AII effects on inositol monophosphate (IP), inositol bisphosphate (IP2) and inositol trisphosphate (IP3) were markedly inhibited. Increasing the Ca2+ concentration to 50 microM or greater fully restored AII-induced inositol phosphates production. AII-induced increases in cytosolic Ca2+ measured by Quin-2 fluorescence, were diminished at lower external Ca2+ concentrations. Treating adrenal glomerulosa cells with Chelex-100, a strong Ca2+ binding resin, blocked early activation of phospholipase C by AII. Inhibition of IP3 production was also observed when inhibitors of Ca2+ movement across the plasma membrane were used, viz., La2+, TMB-8 and nifedipine. The requirement for Ca2+ during AII-induced activation of phospholipase C may be explained, at least partly by a requirement for Ca2+ at a site between the AII receptor and Phospholipase C.
Foster
R H
RH
James A. Haley Veterans Administration Hospital, Tampa, Florida.
Davis
J S
JS
Farese
R V
RV
D000450:Aldosterone / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D004789:Enzyme Activation; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D010738:Type C Phospholipases / Q000378:metabolism*; D015384:Zona Glomerulosa / Q000166:cytology / Q000201:enzymology*
D007295:Inositol Phosphates; D000804:Angiotensin II; D000450:Aldosterone; D010738:Type C Phospholipases; D002118:Calcium