Polylysine-induced rapid Ca2+ release from cardiac sarcoplasmic reticulum.

The rapid kinetics of polylysine-induced Ca2+ release from cardiac sarcoplasmic reticulum (SR) was assessed in combination with its effect on ryanodine binding. SR vesicles were isolated from canine cardiac SR. The time course of SR Ca2+ release was continuously monitored by a stopped-flow apparatus, and [3H]ryanodine binding was done by using the filtration method. The initial rate of polylysine-induced Ca2+ release from cardiac SR revealed different concentration dependence from those observed in skeletal SR. The initial rate peaked at 0.11 microM, followed by a decrease at higher concentrations in skeletal SR, whereas it increased to 3.7 microM in cardiac SR. The [3H]ryanodine binding was also stimulated by polylysine with an identical parallelism with Ca2+ release in terms of polylysine concentration dependence. Thus we demonstrated that the cardiac SR Ca2+ release channel is sensitive to activation by polylysine and that there is a difference in the concentration dependence of polylysine-induced activation of cardiac and skeletal SR Ca2+ release channels.