Role of specific isoforms of protein kinase C in angiotensin II and lipoxygenase action in rat adrenal glomerulosa cells.

Evidence indicates that the lipoxygenase (LO) pathway of arachidonic acid is a key mediator of angiotensin II (AII)-induced aldosterone synthesis in adrenal glomerulosa cells. Although protein kinase C (PKC) may play a role in AII action, the precise PKC isoforms involved and whether LO products can activate PKC is not clear. We therefore evaluated the effect of AII and LO products such as 12- and 15-hydroxyeicosatetraenoic acids (HETEs) on PKC activation in isolated rat adrenal glomerulosa cells. PKC activity was measured by the phosphorylation of a PKC specific peptide while the PKC isoforms were identified by Western immunoblotting using antibodies that recognize the alpha, beta, gamma or epsilon isoforms of PKC. Treatment of the cells for 15 min with AII (10[-8]M) or the LO products 12- or 15-HETE caused a marked increase in PKC activity in membrane fractions with reciprocal decreases in the cytosolic PKC activity. Rat glomerulosa cells expressed only the alpha, and epsilon isoforms of PKC. AII increased membrane bound levels of both PKC-alpha and -epsilon (1.9- and 1.5-fold, respectively), whereas the LO products predominantly activated PKC-epsilon. Reciprocal decreases in immunoreactive cytosolic PKC levels were seen. AII-induced aldosterone synthesis was blocked by H-7 and retinal as well as by a PKC-specific pseudosubstrate inhibitor, PKC(19-36). These results suggest that AII and LO pathway-induced actions in the adrenal glomerulosa may be mediated by specific PKC isoforms.