A phosphorus-31 nuclear magnetic resonance study of the metabolic, contractile, and ionic consequences of induced calcium alterations in the isovolumic rat heart.

Isolated adult rat hearts perfused in an isovolumic mode were used to study the effects of sodium-potassium pump inhibition and sodium-calcium exchange alterations on the tissue content of adenosine triphosphate, phosphocreatine, inorganic phosphate, and intracellular pH, all measured by phosphorus-31 nuclear magnetic resonance spectroscopy. Rates of oxygen consumption, contractile function, and the cell contents of calcium, sodium, and potassium also were determined. The inhibition of sodium-potassium adenosine triphosphatase, either by the reduction in perfusate potassium from 5.9 to 1 millimolar or less, or by the addition of 10(-4) molar ouabain, transiently increased systolic pressure. This was followed by a decrease in systolic pressure, an increase in diastolic pressure, and eventual inexcitability. This contractile profile was accompanied by a persistent increase in oxygen consumption, a monotonic decline in cellular adenosine triphosphate and phosphocreatine content, the development of marked int...