Intracellular cation activities and concentrations in spontaneously hypertensive and normotensive rats.

1. The intracellular concentrations of Na+,K+ and Ca2+ were measured in the erythrocytes of spontaneously hypertensive rats and normotensive Wistar rats. 2. The intracellular Na+ concentration in hypertensive rats was slightly elevated at 3.16 +/- 0.25 compared with 2.85 +/- 0.35 mmol/l (P approximately 0.05) and intracellular Na+ activity was markedly increased in hypertensive rats. 3. Intracellular Ca2+ activity was 7519 +/- 28990 nmol/l of free water in hypertensive rats compared with 123 +/- 98 in controls (P less than 0.01). 4. The cytoplasm of hypertensive animals did not buffer Ca2+ as effectively as that of normal animals. 5. It is concluded that a decreased binding capacity of intracellular macromolecules for Na+ and Ca2+ may explain the disturbances of intracellular electrolyte composition in spontaneously hypertensive rats.