Increased Ca2+ in the sarcoplasm of aortic smooth muscle cells from rats made hypertensive with DOC. A quantitative ultrastructural and cytochemical study.

Uninephrectomized rats were made hypertensive by subcutaneous implantation of pellets of deoxycorticosterone (DOC) and intake of 1% NaCl as drinking solution. Smooth muscle cells from the media of the abdominal aorta of the hypertensive animals and of normotensive rats were studied after fixation in osmium tetroxide containing a calcium precipitating agent (potassium pyroantimonate), a cytochemical method that identifies calcium ions. Specificity of the reaction product was demonstrated by examining samples of the same tissue fixed by a similar solution containing a calcium chelating agent (EGTA). Calcium precipitates were especially numerous in the area of sarcoplasm bordering the nucleus of muscle cells in both groups; in filament rich areas, precipitates were also frequently seen, usually distributed in a linear pattern oriented in the direction of the filaments. Electron opaque reaction product in hypertensive and normotensive rats was quantitated by stereological techniques. Smooth muscle cells from hypertensive animals showed a significant increase in calcium ions within the sarcoplasm (volume density = 0.037 +/- 0.001 SEM) when compared with normotensive controls (volume density = 0.028 +/- 0.002 SEM) (p less than 0.02). The increase in calcium ion in vascular myocytes of hypertensive rats suggest at least in part that intrasarcoplasmic calcium is involved in the pathogenesis of increased arterial tone observed in hypertension.