Uptake of Calcium by Glycerinated Cardiac Slices

Abstract

Partially glycerinated cardiac slices have been used to assess the effects of ryanodine and of mitochondrial and other inhibitors on calcium transport in systems that appear to retain a high degree of functional integrity. Strips of rabbit ventricle were extracted in 50% (w/v) glycerol for 24 hr at 4°C and slices 100 µ thick were cut on the freezing microtome. Such slices can bind 30 to 40 µmole of calcium/g of protein when incubated in medium containing ⁴⁵Ca in the form of a Ca-EGTA buffer, binding being decreased with increasing times of glycerination. The concentrations of ATP and of Ca²⁺ required for halfmaximal activity are 5 x 10^-5 M and 10^-7 M respectively; both ATP and creatine phosphate must be present to elicit maximal uptake. Calcium accumulation appears to be attributable to the sarcoplasmic reticulum rather than to mitochondria, and is inhibited by caffeine, Salyrgan and ryanodine. Uptake is stimulated by oligomycin, but is not affected by azide, ouabain, carbachol, eserine, epinephrine or norepinephrine.