PGE2 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 E2 (PGE2) reverses inhibition of HCO3- absorption (JHCO3) by arginine vasopressin (AVP) by inhibiting AVP-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) production. To determine whether this regulation by PGE2 involves protein kinase C (PKC), MTAL segments were perfused in vitro with physiological solutions containing 25 mM HCO3- (pH 7.4). With 10(-10) MAVP in the bath, addition of 10(-6) M PGE2 to the bath increased JHCO3 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 PGE2 in the bath, addition of staurosporine or chelerythrine to the bath decreased JHCO3 from 12.2 +/- 1.1 to 7.3 +/- 0.6 pmol.min-1.mm-1 (P < 0.005). Neither staurosporine nor chelerythrine affected JHCO3 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 JHCO3 from 5.0 +/- 0.5 to 9.1 +/- 1.0 pmol.min-1.mm-1 (P < 0.01). Similar to PGE2, PMA had no effect on JHCO3 in the absence of AVP or in the presence of 10(-6) M bath forskolin. The effect of PMA to stimulate JHCO3 in the presence of AVP was abolished by pretreatment with pertussis toxin (2 x 10(-11) M). We conclude that 1) PGE2 reverses AVP inhibition of HCO3- absorption by activation of PKC, 2) PKC likely increases JHCO3 by inhibiting AVP-stimulated cAMP production via a Gi-dependent mechanism, and 3) PKC activity has no influence on basal HCO3- absorption rate.
Good
D W
DW
Department of Medicine, University of Texas Medical Branch, Galveston 77555, USA.
D000042:Absorption / Q000187:drug effects; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D001639:Bicarbonates / Q000493:pharmacokinetics*; D015232:Dinoprostone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004789:Enzyme Activation; D008138:Loop of Henle / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001639:Bicarbonates; D010566:Virulence Factors, Bordetella; D001127:Arginine Vasopressin; D037342:Pertussis Toxin; D011493:Protein Kinase C; D015232:Dinoprostone; D013755:Tetradecanoylphorbol Acetate