Calcium paradox in guinea-pig ventricular myocytes

Measurement of the release of lactate dehydrogenase (LDH), the development of contracture and the exclusion of the dye Trypan Blue were made in isolated guinea-pig ventricular myocytes subjected to conditions that evoke a calcium paradox in intact heart. Incubation at 25 degrees C reduced the release of LDH associated with mechanical manipulation of the myocytes so that during prolonged incubation in media free of Ca2+ and Mg2+ ions at 25 degrees C little release of LDH occurred. A significant release of LDH into the incubation media was provoked on repletion of the divalent cations. This release was accompanied by a marked decrease in the percentage of rod-shaped myocytes and their ability to exclude Trypan Blue. The results provide evidence for the existence of the calcium paradox in isolated guinea-pig ventricular myocytes as originally defined.