Regulation of Na+/H+ exchange in mesenteric arteries from spontaneously hypertensive rats.
The kinetic properties of Na+/H+ exchange are significantly different in segments of mesenteric arteries from spontaneously hypertensive rats (SHR) as compared to normotensive Wistar-Kyoto (WKY) rats. Both the maximal rate of Na+/H+ exchange and the sensitivity of Na+/H+ exchange to intracellular [H+] are greater in vessels from hypertensive animals. Prehypertensive SHR do not exhibit these features, thus the present studies examined the role of blood pressure in mediating the response. Both SHR and WKY rats were treated with captopril for 4 weeks, after which the characteristics of the Na+/H+ exchanger were examined. The Na+/H+ exchange was monitored in tissue segments by measuring Nao-dependent, dimethyl amiloride-sensitive recovery of intracellular pH after acid loading (pHi determined using the pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein). In SHR, captopril reduced mean arterial pressure from 153 to 118 mm Hg and altered Na+/H+ exchange. Maximal transport rate decreased from 0.164 to 0.056 mmol/L H+/sec and the sensitivity of the Na+/H+ exchange to internal H+ decreased (ie, the Hill coefficient decreased from 6.6 to 2.2). In WKY rats captopril reduced blood pressure from 108 to 71 mm Hg, but had no effect on the Na+/H+ exchange. Since reduced pressure affected Na+/H+ exchange in SHR, but not in WKY, it is likely that the Na+/H+ exchanger, or the cellular processes regulating its properties, differ in the two rat strains. Supporting this notion was the finding that ouabain treatment reduced the Hill coefficient of SHR vessels but had no effect in WKY vessels.
Department of Physiology, University of Massachusetts Medical School, Worcester 01655.
D R
DR
Ellstrom
C D
CD
Foster
T W
TW
Honeyman
C R
CR
Scheid
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002216:Captopril / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006973:Hypertension / Q000378:metabolism*; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D010042:Ouabain; D002216:Captopril