NA+ H+ EXCHANGE IN PULMONARY-ARTERY SMOOTH-MUSCLE FROM SPONTANEOUSLY HYPERTENSIVE AND WISTAR-KYOTO RATS/

Na+/H+ exchanger regulation of intracellular pH (pH(i)) may play a key permissive role in the mitogen-induced vascular smooth muscle cell gr owth that occurs in systemic and pulmonary vascular remodeling. Sponta neously hypertensive rats (SHR) have increased Na+/H+ exchange in syst emic vessels as well as greater systemic vascular remodeling compared with normotensive Wistar-Kyoto rats (WKY). In contrast to WKY, SHR dem onstrate only mild pulmonary hypertension and no increased remodeling to hypoxia compared with WKY. We therefore wondered whether Na+/H+ exc hange in pulmonary artery smooth muscle (PASM) of SHR might not be ele vated compared with WKY. Baseline PHi, V-max, pK(0.5), and Hill coeffi cient were compared in 12- to 14-wk-old SHR and WKY PASM and aortic sm ooth muscle (AoSM) segments by ratio fluorescence spectroscopy. The V- max, pK(0.5), and Hill coefficient were significantly increased in SHR AoSM segments compared with WKY AoSM segments (53, 0.55, and 53%, res pectively; P < 0.05). There were no differences in these values betwee n SHR and WKY PASM segments, unlike the AoSM segments. We conclude tha t the Na+/H+ exchanger activity in PASM in the SHR is the same as in t he WKY, which is in contrast to systemic arteries where Na+/H+ exchang e is greater in the SHR.