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 arginine vasopressin (AVP) by inhibiting AVP-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production. To determine whether this regulation by PGE(2) involves protein kinase C (PKC), MTAL segments were perfused 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) to the bath increased J(HCO3) from 7.8 +/- 0.4 to 13.0 +/- 1.1 pmol . min(-1). mm(-1) (P < 0.01). This effect was blocked completely by pretreatment with the PKC inhibitors staurosporine or chelerythrine chloride (10(-7) M in the bath). With both AVP and PGE(2) in the bath, addition of staurosporine or chelerythrine to the bath decreased J(HCO3) from 12.2 +/- 1.1 to 7.3 +/- 0.6 pmol . min(-1). mm(-1) (P < 0.005): Neither staurosporine nor chelerythrine affected J(HCO3) under basal conditions 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 increased 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 PMA to stimulate J(HCO3) in the presence of AVP was abolished by pretreatment 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 production via a G(i)-dependent mechanism, and 3) PKC activity has no influence on basal HCO3- absorption rate.