Diastolic tension of rat cardiac muscle during deficiency of oxygen and glucose. Stress-strain relationships and reversibility.

In the isometrically contracting rat trabecular muscle strip preparation, contracture tension was induced either by 10 min of hypoxia (low contracture tension) or by 30 min of joint oxygen and glucose withdrawal (severe contracture tension) at optimum length. Using stepwise 0.1 mm releases, length-tension relationships were recorded under control and contracture conditions in both types of contracture. Stress-strain relationships were evaluated as well as the linear function of the tangent elastic modulus delta sigma/delta epsilon versus stress sigma. The slope of the delta sigma/delta epsilon = f (sigma) function was not significantly changed in low contracture compared to control conditions (n = 8; p less than 0.001). When reversibility tests were performed by reoxygenation after 10 min hypoxia and reperfusion with oxygen and glucose after 30 min of glucose and oxygen withdrawal, low contracture tension was completely abolished after 15 min, whereas 28% of severe contracture was maintained even after 60 min of reperfusion. Additional morphological studies revealed uniform sarcomere lengths in low contracture, and two populations of sarcomere lengths in the severe contracture. On the basis of the present and earlier results, a model of contracture tension generation is proposed in which cross-bridges between actin and myosin cycle at a very low rate and are attached in a force-generating position for a long time.