Effects of digitalis and calcium on papillary muscles in normal and hypoxic states

The effects of digoxin and ouabain in 2.5 and 4.0 mM extracellular calcium were studied in well-oxygenated and hypoxic isolated, isometrically contracting cat papillary muscles. Muscle digoxin content was measured at the conclusion of the digoxin experiments. In the well-oxygenated environment muscles in the higher Ca bathing media reached peak glycoside inotropic effect sooner and contained 2.7 times more digoxin. During hypoxia and reoxygenation muscles contracting with glycosides performed no differently than those without a glycoside present. Muscle digoxin content was lowered at the end of hypoxia (P less than 0.05) in 2.5 mM Ca; after reoxygenation digoxin content was significantly greater than either before or after hypoxia (P less than 0.001). Hypoxic depression of muscle performance was attenuated in 4.0 mM Ca but muscles in 2.5 mM Ca showed greater improvement during reoxygenation even though the muscles in 4.0 mM Ca had significantly greater digoxin content at the end of reoxygenation (P less than 0.02). It therefore is concluded that, although altered extracellular calcium can alter performance during hypoxia and reoxygenation, muscle performance is not aided by the presence of digitalis and under these conditions performance cannot be correlated with muscle digoxin levels.