Characterization of cardiac microsomes from spontaneously hypertonic rats.

Capacity of Ca2+ sequestration was found to be significantly lowered in microsomal preparations of hearts from spontaneously hypertonic rats. A decrease to 40% of the control level was found for basal and extra ATPase. A similar reduction existed in initial and total Ca2+ uptake. These findings are correlated with a lower concentration of the Ca2+ transport ATPase in SDS gel electrophoresis, a lower density of the 7-9 nm intramembraneous particles and higher half-lives of phosphoprotein. Altered contractility of hypertrophied myocardium may thus be partially explained by the dysfunction of the Ca2+ sequestering system.