1. Calcium handling by heart sarcolemmal vesicles from young spontaneously hypertensive rats (SHR) and normotensive Wistar—Kyoto (WKY) control rats were compared.
2. Calcium binding was significantly altered in SHR membranes at the physiological cytosolic Ca2+ concentrations which occur in resting and excited cells.
3. ATP-dependent calcium accumulation occurred at a higher rate in SHR than in WKY rat membrane vesicles.
4. Na+-dependent calcium extrusion of loaded vesicles was higher in SHR than in WKY rat membrane vesicles.
5. These alterations may play a significant role in the pathogenesis of hypertension.