X-ray microanalysis of right ventricular guinea pig myocytes for correllation with NMR measurements of intracellular NA changes after ouabain treatment

Abstract

It is well known that ouabain, a cardiac glycoside, can be used to increase left ventricular contractility. One of the proposed mechanisms of action is the inhibition of Na-K ATPase which leads to an accumulation of Na, which in turn stimulates Ca accumulation via Na-Ca exchange. It has been suggested that the increased calcium is responsible for the augmentation of contractile force. Preliminary studies were designed to measure the intracellular concentrations of Na, Cl, K, and Ca by X-ray microanalysis of freeze-dried cryosections and to compare this data with measurements of intracellular Na made using shift reagent aided 23Na NMR spectroscopy.Male guinea pigs were anesthetized, the hearts excised and perfused using a Langendorff preparation at a pressure of 70cm H2O and at 37°C. A Krebs-Henseleit solution bubbled with 95% O2 - 5% CO2 was used. Ouabain at a concentration of 3 × 10-7 M was added to the perfusate for 30 minutes. This ouabain concentration produces an ionotropic effect without producing a measurable increase in the amount of intracellular sodium as measured by NMR.