Expression and Activity of the Na+/H+ Exchanger NHE-1 in Various Tissues of Spontaneously Hypertensive Rats and Normotensive Wistar-Kyoto Rats

Vascular smooth muscle cells (VSMC) from the spontaneously hypertensive rat (SHR) exhibit an enhanced Na+/H+ exchange activity which coincides with increased proliferation. The aim of the present work was to investigate Na+/H+ exchange activity in VSMC and thymocytes from SHR and Wistar-Kyoto (WKY) rats and to examine the steady state levels of specific Na+/H+ exchanger (isoform 1; NHE-1) mRNA transcripts in VSMC, thymocytes, heart, and kidney.VSMC from SHR proliferated significantly faster than those from WKY rats. NaVH+ exchange activity (Vmax) was significantly (p < 0.01) higher in VSMC from SHR compared to WKY (38 ± 2 vs. 22 ± 1 mmol H+ × liter–1 × min–1; mean ± SE). In contrast, Na+/H+ exchange activity was higher in thymocytes from WKY rats. By Northern blot analysis, we observed similar steady state mRNA levels for NHE-1 in tissues from SHR and WKY, respectively.We conclude that the enhanced Na+/H+ exchange activity found in VSMC from SHR is not expressed in all tissues of SHR. Furthermore, our data suggest that over-expression of NHE-1 is not responsible for the enhanced Na+/ H+ exchange activity in VSMC from SHR. Thus, alterations in cell signalling located upstream of the Na+/H+ exchanger may induce both an increased proliferation and an altered post-translational regulation of Na+/H+ exchange activity in VSMC from SHR.