Simulated acute ischaemia and high cardiac workstates increased myocardial free inorganic phosphate from a baseline of ~0.29 mm to ~3.1 mm and 2.3 mm, respectively.
Computational modeling suggests inorganic phosphate is the primary feedback signal for stimulating oxidative phosphorylation and limits the heart's capacity to hydrolyze ATP in vivo.
Tasa de eventos absoluta: 3.1% vs 0.29%
To understand how cardiac ATP and CrP remain stable with changes in work rate - a phenomenon that has eluded mechanistic explanation for decades - data from (31)phosphate-magnetic resonance spectroscopy ((31)P-MRS) are analysed to estimate cytoplasmic and mitochondrial phosphate metabolite concentrations in the normal state, during high cardiac workstates, during acute ischaemia and reactive hyperaemic recovery. Analysis is based on simulating distributed heterogeneous oxygen transport in the myocardium integrated with a detailed model of cardiac energy metabolism. The model predicts that baseline myocardial free inorganic phosphate (P(i)) concentration in the canine myocyte cytoplasm - a variable not accessible to direct non-invasive measurement - is approximately 0.29 mm and increases to 2.3 mm near maximal cardiac oxygen consumption. During acute ischaemia (from ligation of the left anterior descending artery) P(i) increases to approximately 3.1 mm and ATP consumption in the ischaemic tissue is reduced quickly to less than half its baseline value before the creatine phosphate (CrP) pool is 18% depleted. It is determined from these experiments that the maximal rate of oxygen consumption of the heart is an emergent property and is limited not simply by the maximal rate of ATP synthesis, but by the maximal rate at which ATP can be synthesized at a potential at which it can be utilized. The critical free energy of ATP hydrolysis for cardiac contraction that is consistent with these findings is approximately -63.5 kJ mol(-1). Based on theoretical findings, we hypothesize that inorganic phosphate is both the primary feedback signal for stimulating oxidative phosphorylation in vivo and also the most significant product of ATP hydrolysis in limiting the capacity of the heart to hydrolyse ATP in vivo. Due to the lack of precise quantification of P(i) in vivo, these hypotheses and associated model predictions remain to be carefully tested experimentally.
Wu et al. (Fri,) conducted a other in Normal and ischaemic hearts. Acute ischaemia and high cardiac workstates vs. Baseline state was evaluated on Myocardial free inorganic phosphate (P(i)) concentration. Simulated acute ischaemia and high cardiac workstates increased myocardial free inorganic phosphate from a baseline of ~0.29 mm to ~3.1 mm and 2.3 mm, respectively.