Transport and release of calcium by sarcoplasmic reticulum in chemically skinned ventricular muscle of the rat

Summary Strips of rat ventricle were treated with EGTA (5 mM) for 24 h at 4°C and used to perform isotopical measurements of transport and release of Ca²⁺ in the SR in situ.⁴⁵Ca accumulated by these preparations showed dependence on time of incubation until it reached saturation after 30 min. Rate and capacity of Ca²⁺ accumulation were calculated in 0.075 nmol mg ww^–1 min^–1 and 0.402 nmol mg ww^–1, respectively. These values were increased by a factor of 2.6 and 8.6 when K oxalate was present in the incubation media as could be expected for Ca²⁺ transported by SR.Ca²⁺ release was assayed on⁴⁵Ca desaturation curves at three free Ca²⁺ concentrations: 0.3, 1 and 10 M. Significant increases in the velocity of Ca²⁺ efflux and net release of Ca²⁺ were induced only by 1 M free Ca²⁺, and the Ca²⁺ release could be inhibited by 75% when 50 M of ruthenium red was included in the washout solution.These results are in agreement with those obtained in assessing the SR function by mechanical measurements in skinned cardiac cells or by biochemical determinations in isolated cardiac SR vesicles. In spite of the fact that the resolution time is not as high as that required for the physiological handling of Ca²⁺ by SR, this methodology looks promising for approaching the SR function in cardiac pathologies as well as the effects of drugs on transport and release of Ca²⁺ by cardiac SR.This work was supported by Grant PID 306220088 from the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET).