Use of chlorotetracycline fluorescence to demonstrate Ca²⁺-induced release of Ca²⁺ from the sarcoplasmic reticulum of skinned cardiac cells

Abstract

It has been proposed that the trans-sarcolemmal influx of Ca²⁺ occurring during the plateau of the mammalian cardiac action potential is insufficient in itself to activate the myofilaments, but can trigger a release of Ca²⁺ from the sarcoplasmic reticulum (SR) which is sufficient for activation¹. The demonstration of this Ca²⁺-induced release of Ca²⁺ relied entirely on experiments in which the tension developed by the myofilaments was used as a sensor of the changes of myoplasmic free Ca²⁺ concentration ([free Ca²⁺]) in segments of single cardiac cells from which the sarcolemma had been removed by microdissection (skinned cardiac cells)¹. The small size of these preparations has previously prevented the use of more direct methods for the detection of myoplasmic Ca²⁺ movements^2–4. The present study is a direct demonstration of Ca²⁺-induced release of Ca²⁺ from the SR of skinned cardiac cells treated with chlorotetracycline (CTC), a fluorescent chelate probe which enables changes in the amount of Ca²⁺ bound to a variety of biological membranes or micelles to be monitored^5–8. The fluorescence increases when more Ca²⁺ is bound.