PGE(2) REVERSES AVP INHIBITION OF HCO3- ABSORPTION IN RAT MTAL BY ACTIVATION OF PROTEIN-KINASE-C

In the medullary thick ascending limb (MTAL) of the rat, prostaglandin E(2) (PGE(2)) reverses inhibition of HCO3- absorption (J(HCO3)) by ar ginine vasopressin (AVP) by inhibiting AVP-stimulated adenosine 3',5'- cyclic monophosphate (cAMP) production. To determine whether this regu lation by PGE(2) involves protein kinase C (PKC), MTAL segments were p erfused in vitro with physiological solutions containing 25 mM HCO3- ( pH 7.4). With 10(-10) M AVP in the bath, addition of 10(-6) M PGE(2) t o the bath increased J(HCO3) from 7.8 +/- 0.4 to 13.0 +/- 1.1 pmol . m in(-1). mm(-1) (P < 0.01). This effect was blocked completely by pretr eatment with the PKC inhibitors staurosporine or chelerythrine chlorid e (10(-7) M in the bath). With both AVP and PGE(2) in the bath, additi on of staurosporine or chelerythrine to the bath decreased J(HCO3) fro m 12.2 +/- 1.1 to 7.3 +/- 0.6 pmol . min(-1). mm(-1) (P < 0.005): Neit her staurosporine nor chelerythrine affected J(HCO3) under basal condi tions or in the presence of AVP alone. With AVP in the bath, addition of phorbol 12-myristate 13-acetate (PMA, 10(-6) M) to the bath increas ed J(HCO3) from 5.0 +/- 0.5 to 9.1 +/- 1.0 pmol . min(-1). mm(-1) (P < 0.01). Similar to PGE(2), PMA had no effect on J(HCO3) in the absence of AVP or in the presence of 10(-6) M bath forskolin. The effect of P MA to stimulate J(HCO3) in the presence of AVP was abolished by pretre atment with pertussis toxin (2 x 10(-11) M). We conclude that 1) PGE(2 ) reverses AVP inhibition of HCO3- absorption by activation of PKC, 2) PKC likely increases J(HCO3) by inhibiting AVP-stimulated cAMP produc tion via a G(i)-dependent mechanism, and 3) PKC activity has no influe nce on basal HCO3- absorption rate.