Functions of selected biochemical systems from the exercised-trained dog heart

Abstract

Mitochondria and sarcoplasmic reticulum (SR) fractions were isolated from exercised-trained (E-T) and sedentary control dog hearts. Measurements of mitochondrial respiratory functions indicated no changes in energy-producing (ATP synthesis) capacity in mitochondria from E-T compared to control dog hearts. The ability of isolated mitochondria from E-T hearts to retain accumulated Ca was markedly decreased compared to controls. Inhibition of mitochondrial rates of Ca uptake with the inhibitor, Ru red, revealed fewer binding and/or transport sites in mitochondrial membranes from exercised-trained heart preparations. ATP-dependent binding (- oxalate) and uptake (+ oxalate) of Ca by SR preparations from E-T hearts were unchanged compared to controls. Significant differences in the rates of release of bound Ca were found in SR isolated from E-T hearts. Total myocardial protein, nucleic acids and connective tissue levels were unchanged in E-T hearts compared to controls. Subtle changes seemingly occurred in the energy-utilizing mechanism(s) involving Ca transport of the myocardial cell during exercise training. These changes may be related to alterations in the performance of the exercised-trained heart.