Increased membrane permeability of skin fibroblasts from the spontaneously hypertensive rat

Recently, we have demonstrated several abnormalities in Na+ and K+ homeostasis in cultured vascular smooth muscle cells derived from spontaneously hypertensive rats (SHR). To study whether similar defects can be identified in other cells of this rat strain, 86Rb and 22Na flux experiments as well as measurements of intracellular Na+ and K+ levels were performed in cultured skin fibroblasts of SHR and normotensive Wistar-Kyoto rats (WKY). The efflux rate constant (ke) for Rb+ (K+ analogue) was higher (p less than 0.001) in fibroblasts of SHR than in those of WKY (2.11 +/- 0.03 and 1.66 +/- 0.02 X 10-2/min; mean +/- SEM). The ouabain-insensitive influx rate constant (ki) for Rb+ was also higher (p less than 0.001) in fibroblasts of SHR than in those of WKY (13.26 +/- 0.41 and 10.71 +/- 0.27 X 10-2/min. On the other hand, the activity of the Na+-K+ pump of cells of SHR (44.81 +/- 0.81 X 10-2/min) was not different from that of cells of WKY (44.72 +/- 0.47 X 10-2/min). This parameter was obtained by calculating the ouabain-sensitive Rb+ influx rate constant. There was also no difference in the Na+ uptake (in the presence of ouabain) between cells of the two rat strains. Although there was no statistically significant difference in the measured intracellular total K+ levels between the two groups, on the basis of equilibrium distribution of 86Rb+, we calculated a significantly lower (p less than 0.001) level of exchangeable intracellular K+ in fibroblasts of SHR (98.2 +/- 1.2 mEq/L) as compared with cells of WKY (115.3 +/- 1.5 mEq/L). These findings indicate increased membrane permeability to K+ in fibroblasts of SHR and that this defect is likely to be innate to their membrane structure.