title: The effect of calcium depletion upon the tension-independent component of cardiac heat production.
abstract: Rabbit papillary muscle has been exposed to calcium concentrations ranging from 2.5 mM to zero. Its mechanical and electrical activity has been monitored and its heat production measured using a myothermic technique. Calcium depletion decreased the magnitude of the tension-independent heat per contraction from a mean of 0.45 mcal/g muscle to 0.31 mcal/g muscle at room temperature (18 degrees to 22 degrees C). Calcium-chelating agents did not abolish action potential conduction under the experimental conditions used but they further reduced the magnitude of the tension-independent heat. Raising the temperature from room level to 32 degrees C decreased the tension-independent heat from a mean of 0.52 to a mean of 0.24 mcal/g muscle. Calcium depletion at 32 degrees C further decreased this heat and it was calculated that the energy now liberated in activating the muscle was about 2% of the total energy normally liberated in the working heart. The results are interpreted in terms of current biochemical and myothermic data.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects*; D002118:Calcium / Q000494:pharmacology*; D002151:Calorimetry; D002614:Chelating Agents / Q000494:pharmacology; D002951:Citrates / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004594:Electrophysiology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects*; D011817:Rabbits; D013696:Temperature
chemical_list: D002614:Chelating Agents; D002951:Citrates; D004492:Edetic Acid; D002118:Calcium