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 anti-bodies (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 μg 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 μg 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 V(max) 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 μg protein, from SHR and WKY, respectively) or in freshly isolated thymocytes (0.158±0.046 vs 0.226±0.054 O.D. units/10 μg protein, from SHR and WKY, respectively). We conclude that the increase in the V(max) 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.