NHE-1 protein in vascular smooth muscle and lymphocytes from the spontaneously hypertensive rat

The present study examined the abundance of NHE-1 protein in cultured vascular smooth muscle cells (VSMCs), freshly isolated thymocytes, and fresh aortic tissue from spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rats. Two sets of affinity-purified antibodies (Ab[765-778] and Ab[698-711]) against different epitopes of the NHE-1 isoform of the Na+-H+ antiporter were used. Each set of antibodies recognized a major protein band at 105 to 110 kD that was more abundant in protein lysates prepared from cultured VSMCs from the SHR than those from WKY rats (Ab[765-778] 0.047 +/- 0.011 vs 0.010 +/- 0.002 O.D. units/10 microg protein, P<.001 for SHR and WKY, respectively; and Ab(698-711) 0.173 +/- 0.026 vs 0.087 +/- 0.028 O.D. units/10 microg protein, P<.05, for SHR and WKY, respectively). The increase in NHE-1 protein abundance in cultured VSMCs from the SHR was associated with a greater Vmax of the Na+-H+ antiporter as compared to those from WKY rats (17.93 +/- 2.07 vs 8.16 +/- 1.05 mmol H+/min, P<.001, respectively). In contrast to cultured VSMCs, there was no difference in the relative abundance of NHE-1 protein in fresh aortic tissue (0.075 +/- 0.018 vs 0.083 +/- 0.017 O.D. units/10 microg protein, from SHR and WKY, respectively) or in freshly isolated thymocytes (0.158 +/- 0.046 vs 0.226 +/- 0.054 O.D. units/10 microg protein, from SHR and WKY, respectively). We conclude that the increase in the Vmax of the Na+-H+ antiporter in cultured VSMCs from the SHR, compared to those from WKY rats, is due, at least in part, to increased levels of NHE-1 protein.