Calcium sequestration by subcellular fractions isolated from vascular smooth muscle: Effect of cyclic nucleotides and prostaglandins

Microsomal vesicles and mitochondria derived from aortae of rat accumulate calcium in the presence of adenosine triphosphate and magnesium. The rate and extent of energy-linked calcium sequestration by microsomal vesicles were found to exhibit hydrogen ion and temperature dependency and nucleoside phosphate specificity. Calcium uptake (in the presence of oxalate) showed preference for nucleosides in the order ATP>ADP>GTP>UTP>ITP. Calcium accumulation by the subcellular fractions was also found to be dependent upon the concentration of calcium in the incubation medium. Cyclic AMP stimulated microsomal calcium binding while prostaglandins F_2α and E₂ had no specific effect. These agents did not alter the calcium sequestering mechanisms of the mitochondria. These data suggest that the vesicular and mitochondrial fraction may constitute an important factor in the regulation of calcium availability to the contractile mechanism of vascular smooth muscle.