Comparative studies on the calcium paradox in cardiac muscle: the effect of temperature on the different phases.

By measuring characteristic ultrastructural damage, the Ca2+-paradox has been demonstrated in isolated frog hearts, and in frog and mouse ventricle strips. During Ca2+-free perfusion (phase I), PCa of the sarcolemma is increased; 4 degrees C provides complete protection against these molecular changes in frog and a partial protection in mouse tissue. Re-introduction of extracellular Ca2+ (phase II) now causes typical Ca2+-triggered damage which is markedly reduced at 4 degrees C in both species but is not inhibited by leupeptin. Major sarcolemma damage occurs at this point.