title: Angiotensin II inhibits HCO-3 absorption via a cytochrome P-450-dependent pathway in MTAL.
abstract: The role of ANG II in the regulation of ion reabsorption by the renal thick ascending limb is poorly understood. Here, we demonstrate that ANG II (10(-8) M in the bath) inhibits HCO-3 absorption by 40% in the isolated, perfused medullary thick ascending limb (MTAL) of the rat. The inhibition by ANG II was abolished by pretreatment with eicosatetraynoic acid (10 microM), a general inhibitor of arachidonic acid metabolism, or 17-octadecynoic acid (10 microM), a highly selective inhibitor of cytochrome P-450 pathways. Bath addition of 20-hydroxyeicosatetraenoic acid (20-HETE; 10(-8) M), the major P-450 metabolite in the MTAL, inhibited HCO-3 absorption, whereas pretreatment with 20-HETE prevented the inhibition by ANG II. The addition of 15-HETE (10(-8) M) to the bath had no effect on HCO-3 absorption. The inhibition of HCO-3 absorption by ANG II was reduced by >50% in the presence of the tyrosine kinase inhibitors genistein (7 microM) or herbimycin A (1 microM). We found no role for cAMP, protein kinase C, or NO in the inhibition by ANG II. However, addition of the exogenous NO donor S-nitroso-N-acetylpenicillamine (SNAP; 10 microM) or the NO synthase (NOS) substrate L-arginine (1 mM) to the bath stimulated HCO-3 absorption by 35%, suggesting that NO directly regulates MTAL HCO-3 absorption. Addition of 10(-11) to 10(-10) M ANG II to the bath did not affect HCO-3 absorption. We conclude that ANG II inhibits HCO-3 absorption in the MTAL via a cytochrome P-450-dependent signaling pathway, most likely involving the production of 20-HETE. Tyrosine kinase pathways also appear to play a role in the ANG II-induced transport inhibition. The inhibition of HCO-3 absorption by ANG II in the MTAL may play a key role in the ability of the kidney to regulate sodium balance and extracellular fluid volume independently of acid-base balance.
mesh_terms: D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D016227:Benzoquinones; D001639:Bicarbonates / Q000493:pharmacokinetics*; D000242:Cyclic AMP / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019833:Genistein / Q000494:pharmacology; D006893:Hydroxyeicosatetraenoic Acids / Q000494:pharmacology; D007679:Kidney Medulla / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D047029:Lactams, Macrocyclic; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011809:Quinones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction / Q000502:physiology; D012964:Sodium / Q000378:metabolism