Enzyme-substrate interactions in the hydrolysis of peptides by cathepsins B and H from rat liver.

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.