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Phosphagen content breakdown during contraction and oxygen consumption in rat portal vein


, : Phosphagen content breakdown during contraction and oxygen consumption in rat portal vein. American Journal of Physiology 244(3): C250-C258

The stoichiometric relation between breakdown of high-energy phosphate compounds (phosphagens) during contraction and O2 consumption was studied in rat portal vein under conditions in which periodic spontaneous isometric contractions were maintained. To characterize the rate of energy turnover with the time during a maintained contracture, O2 consumption and net phosphagen breakdown were also measured during high-K+-induced contactures. By means of analytical isotachophoresis, a phosphocreatine (PCr) breakdown during a spontaneous contraction (duration 6-8 s) of 0.39 .+-. 0.12 (SE) .mu.mol/g (n = 10) was determined, with no change in ATP, ADP or AMP. This value was corrected for resynthesis during contraction and compared with the tension-dependent O2 consumption. The results indicate an ATP resynthesis of .apprx. 6.4 mol/mol O2, which agrees with an ADP/O ratio of 3. During high-K+-induced contractures the O2 consumption rate (JO2) reached a maximum of .apprx. 2.5 times the basal value in the first 1-2 min, while force was still increasing. A net PCr breakdown of 0.78 .+-. 0.23 .mu.mol/g (n = 8) occurred in the 1st min. In the subsequent maintained contraction, JO2 was twice the basal value and no net phosphagen breakdown occurred between the 1st and 10th min of contraction. The suprabasal rate of phosphagen turnover during the 1st min is thus 1.8 times the steady rate at the force plateau, consistent with a possible change in cross-bridge kinetics in the course of contraction. The concentration of free ADP was calculated assuming equilibrium of the Lohmann reaction and was found to vary in a similar way as JO2 under the different contractile situations investigated.

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