Evidence for increased in vivo sodium-potassium pump activity and potassium efflux in skeletal muscle of spontaneously hypertensive rats
We have used87Rb nuclear magnetic resonance spectroscopy (NMR) to study in vivo rubidium kinetics in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) controls, using rubidium as a marker for potassium. We gave 15 male, 13-week-old SHR, mean ± s.d. blood pressure 180 ± 10mmHg, and 15 age-matched normotensive controls, mean blood pressure 120±9mmHg, a daily dose of RbCl (2 mmol/kg intraperitoneally). We made repeated NMR measurements of skeletal muscle rubidium concentrations until steady state was reached. We then withdrew rubidium and made further measurements of rubidium concentrations, at intervals, for up to 1 week after the last injection. We also measured plasma and erythrocyte rubidium concentrations by flame atomic absorption spectroscopy at similar intervals after the withdrawal of rubidium. Rubidium concentrations rose at a faster rate in SHR skeletal muscle, but the steady-state muscle rubidium concentration was the same (45 mmol/l) in both SHR and WKY rats. There was also a threefold increase in the rate of rubidium efflux from both muscle and erythrocytes in SHR. These results are consistent with a marked increase in Na+, K+-ATPase activity and an increase in the rate of rubidium efflux in vivo in SHR. The increased rate of rubidium efflux in SHR could represent increased K+efflux via calcium-activated K+channels and/or result as part of cell volume regulation secondary to increased Na+-H+antiporter activity. © Current Science Ltd.