Recording of calcium transient and analysis of calcium removal mechanisms in cardiac myocytes from rats and ground squirrels

With confocal microscopy, we recorded calcium transients and analyzed calci um removal rate at different temperatures in cardiac myocytes from the rat, a non-hibernator, and the ground squirrel, a hibernator. The results showe d a remarkable increase of the diastolic level of calcium transients in the rat but no detectable change in the ground squirrel. Calcium transient of the ground squirrel, compared with that of the rat at the same temperature, had a shorter duration and showed a faster calcium removal. As indicated b y the pharmacological effect of cyclopiazonic acid, calcium uptake by sarco plasmic reticulum (SR) was the major mechanism of calcium removal, and was faster in the ground squirrel than in the rat. Our results confirmed the es sential role of SR in hypothermia-tolerant adaptation, and negated the impo rtance of Na-Ca exchange. We postulated the possibility to improve hypother mia-tolerance of the cardiac tissue of non-hibernating mammals.