Energy dependence of contraction band formation in perfused hearts and isolated adult myocytes.

Aggregation of sarcomeres into contraction bands is a prominent feature of the oxygen paradox, the calcium paradox, and caffeine injury to calcium-free perfused hearts. For investigation of the mechanism of contraction banding, it was necessary to devise a method of evaluating the degree of sarcomere contraction and to define objectively a contraction band. Hearts with mechanical detachment of cells caused by hypocalcemic perfusion and isolated myocytes both allow unrestrained contracture of cells and permit direct optical measurements to quantitate the degree of cell contracture. With the use of the calcium paradox as a model of contraction band necrosis, it was found that cells with lengths of less than 37.3 mu could be considered as containing contraction bands. It was found that the mitochondrial inhibitors cyanide and amytal, as well as the uncoupler 2,4-dinitrophenol, allowed cell contracture but inhibited hypercontracture of sarcomeres into contraction bands during both the calcium paradox and caffeine injury to perfused hearts. However, when 2mM adenosine triphosphate (ATP) was included in the perfusion media, contraction band formation occurred despite the continued presence of cyanide or amytal. In isolated myocyte preparations the addition of the glycolytic inhibitor iodoacetate (IAA, 5 mM) and the mitochondrial inhibitor amytal (3 mM) caused relaxed rod-shaped cells (length/width ratio greater than 3:1) to contract into a stable population of square-shaped forms (length/width ratio less than 3:1), indicating an abrupt and severe decline in cellular ATP levels. Removal of amytal from the incubation medium in the presence of IAA produced a significant conversion of square-shaped cells into round-shaped cells containing contraction bands. Either IAA alone or amytal alone resulted in a mixed population of square and round cells. The results indicate that ATP is required for the formation of contraction bands in intact hearts and for the rounding of isolated myocytes. Formation of contraction bands appears to be an energy-dependent process requiring ATP.