Alterations in Na(+)-H+ exchange in mesenteric arteries from spontaneously hypertensive rats.
Na(+)-H+ exchange was examined in segments of the superior mesenteric artery from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats using the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Basal pH values were identical in the two strains (SHR = 7.18 +/- 0.02, WKY = 7.15 +/- 0.01) and exposure to 20-50 mM NH4Cl produced comparable changes in pH in both strains (tissues acidified to pH 6.8). The recovery of intracellular pH (pH(i)) from acid loading in bicarbonate-free buffer was dependent on extracellular Na+, inhibited by dimethyl amiloride, and thus was presumably mediated by Na(+)-H+ exchange. Exchange activity was markedly increased in SHR (0.308 vs. 0.182 pH U/min), and the increased activity could not be explained by differences in intracellular buffer capacity or in the Na+ affinity of the transporter. The rate of Na(+)-H+ exchange was more steeply dependent on pH(i) in SHR vessels Hill coefficient = 6.6 in SHR vs. 4.1 in WKY), suggesting an alteration in the transport protein. Young SHR (4-6 wk) exhibited kinetic characteristics resembling those of 12- to 14-wk-old WKY rats. Exposure to the Ca2+ ionophore bromo-A23187 significantly increased the Hill coefficient of WKY arteries but had no effect on vessels from SHR. Exposure of vessels from either strain to the phorbol ester phorbol 12-myristate 13 acetate (PMA) had no effect on Na(+)-H+ exchange.
Foster
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CD
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
Honeyman
T W
TW
Scheid
C R
CR
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D002021:Buffers; D002352:Carrier Proteins / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008638:Mesenteric Arteries / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR / Q000378:metabolism* / Q000502:physiology; D011921:Rats, Inbred WKY; D012964:Sodium / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002021:Buffers; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; C039465:5-dimethylamiloride; D000584:Amiloride; D012964:Sodium; D013755:Tetradecanoylphorbol Acetate