²²Na⁺ and ⁸⁶Rb⁺ transport in vascular smooth muscle of SHR, Wistar Kyoto, and Wistar rats

To gain further insight into differences in cellular Na⁺ and K⁺ regulation between the spontaneously hypertensive rat (SHR), Wistar Kyoto (WKY), and American Wistar (W) rats, ²²Na⁺ and ⁸⁶Rb⁺ washouts were performed under steady-state conditions in cultured vascular smooth muscle cells from the three rat strains. SHR vascular smooth muscle cells showed significantly higher bumetanide sensitive ⁸⁶Rb⁺ washout rate constant (x 10^-4/min; mean ± SEM) than WKY cells (-38.6 ± 2.84 and -23.8 ± 3.58, respectively; p < 0.005). SHR vascular smooth muscle cells also exhibited significantly higher values than WKY in cells in the total ²²Na⁺ washout rate constant (x 10^-2/min) (-61.0 ± 1.57 vs. -53.8 ± 1.24; p < 0.005). The amiloride sensitive component of the ²²Na⁺ washout rate constant accounted for these differences (-18.6 ± 1.04 for SHR and -12.1 ± 2.00 for WKY; p < 0.05). There were no apparent differences in cellular Na⁺ concentrations between WKY and SHR cells. In general, the ⁸⁶Rb⁺ and ²²Na⁺ washout parameters of W rat cells were quite similar to those of cells from SHR. We conclude that the bumetanide-sensitive ⁸⁶Rb⁺ washout (the Na⁺ K⁺-cotransport), the overall, and the amiloride-sensitive ²²Na⁺ washout (the latter primarily represents the Na⁺/H⁺ antiport) are higher in SHR than WKY rat vascular smooth muscle cells. These findings indicate innate differences in cellular Na⁺ and K⁺ transport in vascular smooth muscle cells of the SHR and WKY rat. The mechanisms responsible for these differences are yet to be determined.