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 growth that occurs in systemic and pulmonary vascular remodeling. Spontaneously hypertensive rats (SHR) have increased Na+/H+ exchange in systemic vessels as well as greater systemic vascular remodeling compared with normotensive Wistar-Kyoto rats (WKY). In contrast to WKY, SHR demonstrate only mild pulmonary hypertension and no increased remodeling to hypoxia compared with WKY. We therefore wondered whether Na+/H+ exchange in pulmonary artery smooth muscle (PASM) of SHR might not be elevated compared with WKY. Baseline PHi, V-max, pK(0.5), and Hill coefficient were compared in 12- to 14-wk-old SHR and WKY PASM and aortic smooth 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%, respectively; P < 0.05). There were no differences in these values between SHR and WKY PASM segments, unlike the AoSM segments. We conclude that the Na+/H+ exchanger activity in PASM in the SHR is the same as in the WKY, which is in contrast to systemic arteries where Na+/H+ exchange is greater in the SHR.