CGMP ANTAGONIZES ANGIOTENSIN-MEDIATED PHOSPHATIDYLCHOLINE HYDROLYSIS AND C-KINASE ACTIVATION IN MESANGIAL CELLS

Previous studies from this laboratory have shown that in cultured rat mesangial cells (MC), angiotensin II (ANG II) mediates its effects via activation of phosphatidylinositol-specific phospholipase C (PI-PLC) and phosphatidylcholine-specific phospholipase C (PC-PLC) and phosphol ipase D (PC-PLD). In addition, guanosine 3',5'-cyclic monophosphate (c GMP)-elevating maneuvers that stimulate particulate and soluble guanyl ate cyclase [atrial natriuretic factor (ANF) and sodium nitroprusside (SNP), respectively] antagonize ANG II-mediated PI-PLC activation. The current study explored whether cGMP impairs ANG II-mediated PC-PLC an d PLD activity. The ANG II-stimulated release of the water-soluble met abolites of PC breakdown (phosphorylcholine and choline) was blocked b y ANF and SNP. ANG II-stimulated phosphatidic acid and phosphatidyleth anol formation were significantly reduced by ANF and SNP, confirming t hat cGMP blunted PLD activity. The inhibitory effect of cGMP on PLD co uld be reversed by N-(2-[methylamino]ethyl)5-isoquinolinesulfonamide, a blocker of cGMP-dependent protein kinase. In parallel experiments, A NF and SNP abrogated sustained diacylglycerol (DAG) accumulation deriv ed from ANG II stimulation of PC hydrolysis, confirming that cGMP dimi nished PC-PLC activity. Inhibition of PC-derived DAG accumulation by c GMP was associated with a concomitant decrement in ANG II-mediated tra nslocation of protein kinase C (PKC) activity from the cytosol to the membrane. In summary, in MC, cGMP antagonizes ANG II-mediated PC hydro lysis, DAG formation, and PKC activation. We propose that cGMP-mediate d inhibition of phospholipid metabolism and PKC translocation plays an important role in MC vasorelaxation.