Cation sensitivity of inositol 1,4,5-trisphosphate production and metabolism in agonist-stimulated adrenal glomerulosa cells.

Angiotensin II (AII) evokes a biphasic increase in inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) levels in adrenal glomerulosa cells, with an extracellular Ca(2+)-independent early peak followed by a secondary sustained elevation that is highly dependent on the presence of extracellular Ca2+. The Ca(2+)-dependent sustained phase of agonist-induced Ins(1,4,5)P3 production was closely correlated with Ca2+ influx and was inhibited by inorganic Ca2+ channel blockers with the potency ratio: La3+ >> Cd2+ > Mn2+ > Co2+ > Ni2+. Of the two Ca2+ surrogates, Sr2+ and Ba2+, Sr2+ was partially active compared with Ca2+, and Ba2+ was inactive in restoring Ins(1,4,5)P3 formation in cells stimulated with AII in Ca(2+)-free medium. However, unlike Ca2+, Sr2+ only weakly supported and Ba2+ failed to affect the calmodulin-activation of Ins(1,4,5)P3 3-kinase. Also, there was an accumulation of Ins(1,4,5)P3 and diminished formation of Ins(1,3,4,5)P4 and Ins(1,3,4)P3 when intact glomerulosa cells were stimulated by AII in the presence of Sr2+. This difference between the Sr2+ sensitivity of phospholipase C and Ins(1,4,5)P3 3-kinase provides a means for the potentiation of agonist-induced elevations of Ins(1,4,5)P3 in the intact cell and for direct analysis of the role of the inositol tris-/tetrakisphosphate pathway in cellular signaling.