Cardiac sarcoplasmic reticulum characteristics in hypertrophic hearts from spontaneously hypertensive rats

Sarcoplasmic reticulum (SR) from left ventricles of rats that developed spontaneous hypertension was studied in vitro. Similar increases of left ventricular mass were found when grouping the animals into mild and severe hypertensives (average systolic arterial pressure of 168±4 and 202±6 mm Hg, respectively). The amount of SR protein (mg/g of left ventricle) was higher when obtained from hypertrophic ventricles of both hypertensive groups than from ventricles of the control group. The result agreed with the enhanced Ca2+ uptake exhibited by left ventricular homogenates of the hypertensive groups. Consequently, Ca2+ uptake in SR microsomes isolated per gram of left ventricle (nmol Ca2+/g muscle) was 51.62±10.06 and 64.99±12.84 in mildly and severely hypertensive groups vs. 17.37±5.79 in the control group (P<0.05). The SR microsomes obtained from ventricles of hypertensive rats showed an enhanced Ca2+ activated ATPase activity that was not accompanied by increased Ca2+ uptake at saturating calcium concentrations, but by increased affinity for calcium (K'app of 1.09±0.28 and 2.67±0.16 μM in SR microsomes of hypertrophic and control ventricles respectively; P