Abstract
The different intracellular cation-contents present in the right and left ventricle depend on varying Ca 2+-concentrations. The effect of extracellular Ca 2+-concentrations varied within the physiological range has been studied on an isolated guinea pig heart preparation, showing excellent stable experimental conditions. By increasing the extracellular Ca 2+-concentration from 0.45 m m to 3.6 m m the tissue contents of calcium and potassium were increased dependent on [Ca] e whereas that of Na was reduced. This was due to a change in the composition of the intracellular cations as the extracellular space (inulin) and water-content of the heart muscle tissue were not influenced by increasing the extra-cellular Ca 2+-concentration. At any given [Ca] e the Ca- and Na-content of the right ventricular myocardium was higher than that in the left. The ratio Ca right Ca left varied from 2.0 at 0.45 m m to 1.6 at 3.6 m m [Ca] e. The left ventricular contractile force showed a log linear relationship to Ca net as well as [Na] i.
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