[Calcium accumulation in hyperpermeable fibers of vascular smooth, skeletal and cardiac muscle of rats].

This work presents results on calcium accumulation capacity of chemically skinned multifiber preparations of aortic smooth, skeletal and ventricular muscle of the rat. The suppression of the plasma membrane functions as a permeability barrier to ions, allowed to expose the sarcoplasmic reticulum (SR) to 45Ca-EGTA buffers and to measure the amount of 45Ca accumulated by the preparations in a 30-min period at room temperature. The 45Ca loaded was attributed to the activity of the SR calcium pump since it was dependent on pCa values of the incubation media and enhanced by K oxalate. This method allowed to discriminate calcium accumulation capacity of SR in the different muscle types. 45Ca accumulated in the absence of K oxalate amounted to 5.16 +/- 0.08, 7.02 +/- 0.38 and 2.59 +/- 0.15 mumoles Ca2+/g fiber protein in aortic smooth, skeletal and ventricular muscle preparations, respectively. The values obtained in the presence of 10 mM K oxalate indicated the following increasing order of calcium accumulation capacities: skeletal greater than ventricular greater than or equal to aortic smooth muscle. Taking into account the protein content of each muscle type, the calculated amount of calcium accumulated by the SR exceeds that necessary to elicit full contractile activation.