Suspension of smooth muscle cells treated with digitonin as a model for studying the myometrial endoplasmic reticulum calcium pump.

The effect of the nonionic detergent digitonin on ruthenium red-insensitive, oxalate-stimulated, and thapsigargin-suppressed accumulation of Ca2+ by suspension of myometrial cells from ATP- and Mg(2+)-containing incubation medium was studied using passive loading with 45Ca2+. The dependence of Ca2+ accumulation by the cells on the concentration of digitonin is bell-shaped, the maximal Ca2+ uptake being observed at 0.05-0.1 mg/ml digitonin. Myocytes chemically skinned with digitonin represent a suitable experimental model for studying kinetic properties of the uterine myocyte endoplasmic reticulum Mg2+, ATP-dependent Ca2+ pump and assessing sensitivity of this Ca(2+)-transporting system to various effectors including the uterotonic octapeptide oxytocin.