INDIRECT INHIBITION BY BRADYKININ OF CYCLIC-AMP GENERATION IN ISOLATED RAT GLOMERULI AND MESANGIAL CELLS

The present study was designed to evaluate the effect of the activatio n of bradykinin (BK) receptors on intracellular cAMP levels in isolate d glomeruli as well as in cultured rat mesangial cells. BK affected ba sal cAMP content only in the presence of the phosphodiesterase inhibit or isobutylmethylxanthine. Furthermore, BK inhibited forskolin-, prost aglandin E2-, and isoproterenol-stimulated cAMP accumulation, both in the presence and in the absence of isobutylmethylxanthine. The inhibit ory effect of BK was independent of stimulation of cAMP degradation by phosphodiesterase. No direct inhibition of the in vitro adenylyl cycl ase activity was observed, suggesting a requirement for cytoplasmic co nstituents. Use of the phospholipase A2 inhibitor mepacrine and treatm ent with pertussis toxin did not modify the inhibitory effect of BK, i ndicating that neither the phospholipase A2 pathway nor the inhibitory G protein is involved. The effect of BK was completely prevented by t wo selective protein kinase C (PKC) inhibitors, staurosporine and bisi ndolylmaleimide. Furthermore, use of the diacylglycerol analog 1-oleoy l-2-acetyl-rac-glycerol and direct activation of PKC with phorbol-12-m yristate-13-acetate mimicked the effect of BK, whereas the biologicall y inactive phorbol ester 4alpha-phorbol-12,13-didecanoate was without effect. Furthermore, down-regulation of PKC by long term pretreatment with phorbol-12-myristate-13-acetate abolished the inhibitory effect o f BK on stimulated cAMP levels. These results demonstrate that BK inhi bits forskolin-, prostaglandin E2-, and isoproterenol-stimulated cAMP formation through activation of the phospholipase C pathway. The subse quent production of diacylglycerol associated with stimulation of PKC in turn inhibits stimulated cAMP accumulation.