Effects of Ions, Ouabain, Epinephrine, and Tetrodotoxin on Glucose Metabolism and on Contractility in the Perfused Guinea Pig Heart

Abstract

In the perfused guinea pig heart, the rate of glucose-U-14C oxidation to 14CO2 was directly related to the external ratio [Ca2+]/[Na+]2. The metabolic stimulatory effects of ouabain were concentration-dependent, and those brought about by epinephrine were not prevented by the presence of ouabain or added Ca2+. The increased glucose utilization produced by ouabain or Ca2+ was reduced by tetrodotoxin (TTX), whereas that produced by epinephrine or reduced extracellular Na+ (100 mM) was not. It was also found that TTX inhibited the positive inotropic effects of Ca2+ and ouabain, but did not reduce the contractile force during perfusion in presence of epinephrine or at 100 mM Na+. It is concluded that (a) ouabain (or Ca2+) and epinephrine, producing additive effects, have different modes of action; (b) TTX and ouabain (or Ca2+) have antagonistic effects, probably resulting from their opposite action on calcium movements.