Effect of frequency and Ca++ concentration on oxygen consumption of the isolated rat heart

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Abstract
The consumption of isolated rat hearts perfused according to Latigendorff was measured at various frequencies of stimulation and at various Ca++ concentrations. A distinction was made between the resting O2 consumption (QO2r) and the O2 consumption and frequency was observed. By extrapolating this relationship to 0 frequency the resting O2 consumption QO2r and the QO2c per contraction were calculated. At the normal Ca++ concentration of 2.6 meq/liter, the determined values were: QO2r =2-30 [plus or minus] -15 [mu]moles O2/g per min., and QO2c per contraction: 6.8 [plus or minus] 0.5 m[mu] moles 62/g. This last value was independent of the frequency of stimulation. An increase of the Ca++ concentration in the perfusion fluid produced a proportional Increase In the measured values of QO2r whereas QO2c per contraction remained the same in spite of an increased amplitude of contraction. A decrease of the Ca++ concentration in the perfusion fluid from 2.6 to 0.5 meq/liter did not result in a difference In the corresponding QO2r values. Dut tne value of QO2c per contraction was drastically reduced.

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