Physical and biochemical energy balance during an isometric tetanus and steady state recovery in frog sartorius at 0 degree C.

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Abstract
Frog sartorius muscle stimulated isometrically for 3 s every 256 s to attain a steady state in which initial heat (QI), recovery heat (QR), rate of O2 consumption (JO2) and isometric force (Po) generated are constant for each cycle. For a 3-s tetanus given every 256 s, JO2 was 0.106 .mu.mol/(min.cntdot.g blotted wt), .apprx. 71% of the maximum rate observed, whereas lactate production was negligible under these conditions. QI, QT (= QI + QR), and QT/QI were 88.2, 181.5, 2.06 mJ/g blotted weight, respectively. The high-energy phosphate breakdown (.DELTA. .apprx. P) breakdown during the first 3-s tetanus was not different from that during a contraction in the steady state and averaged 1.1 .mu.mol/g blotted wt. Less than half of the initial heat could be accounted for in terms of the extent of the known chemical reactions occurring during contraction. From the stoichiometry of the theoretical biochemical pathways, the amount of ATP synthesized in the steady state exceeds .DELTA. .apprx. P during contraction by > 2-fold, corresponding to an apparent ADP:O2 ratio of 1.5. If it is assumed that carbohydrate oxidation is the only net chemical reaction in the steady state, the total heat production can be explained on the basis of the measured JO2. Heat production during recovery was less than that expected on the basis of the O2 consumption and .DELTA. .apprx. P during contraction. The unexplained enthalpy production and low apparent ADP:O2 ratio are causally related, i.e., that the reaction(s) producing the unexplained heat during contraction is reversed during the recovery period.