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Free Ca2+ in the cytosol (Ca2+i) of individual rat ventricle cells injected with aequorin was measured under anoxia. In glucose-free medium myocytes spontaneously shortened after about 60 min, although Ca2+i was still at or near resting levels. However, within minutes a net inward movement of Ca2+ across the sarcolemma developed and Ca2+i began to rise. Provided oxygen was readmitted before Ca2+i exceeded 2-3 microM, cells were able to restore Ca2+i to resting levels through caffeine-sensitive sequestration of Ca2+ in the sarcoplasmic reticulum. We suggest that Ca2+-independent shortening of anoxic cardiomyocytes reflects onset of rigor which triggers loss of Ca2+i homoeostasis.
Allshire et al. (1987) studied this question.