ATP turnover rates

Figure 2. Force generation and energy metabolism in human quadriceps femoris muscle stimulated intermittently at 20 Hz, with 1.6 sec tetani with 1.6 sec rest periods between tetani. The upper panel shows force, ATP turnover rate, and pH the middle panel, the concentrations of PCr, P and lactate and the lower panel, ATP, ADP, IMP, H, and calculated H2PO4. From Hultman et al. (1990), with permission from Human Kinetics Publishers.

Figure 2 shows the expected changes during an intense contraction an 80% decrease in force generation and a comparable decrease in ATP turnover rate. The ATP content was decreased by about 40% and PCr by 95%. At the same time large increases were observed in and P,. 

Katz, A., Sahlin, K., Henriksson, J. (1986b). Muscle ATP turnover rate during isometric contraction in humans. J. Appl. Physiol. 60, 1839-1842. 

E. L. Lim, K. G. Hollingsworth, P. E. Thelwall and R. Taylor, Measuring the acute effect of insulin infusion on ATP turnover rate in human skeletal muscle using phosphorus-31 magnetic resonance saturation transfer spectroscopy. NMR Biomed., 2010, 23,952-957. 

To figure out the biological meaning of the crossover (Figure 2.9 (C-E)), we need to know why this occurs. In mammals the answer seems to be a simple conseqence of power obtainable from different metabolic pathways maximum ATP turnover rates supported by fat oxidation in mammals are only about two-thirds the maximum ATP turnover rates supportable by glycogen oxidation (figure 2.10). The reasons for... 

ADP monitored simultaneously in human gastrocnemius and soleus during three different exercise intensities, 20%, 30%, and 40% of maximum (bars), with rest periods in between and recovery at the end of the protocol. To standardize the data, PCr and ATP are expressed as the ratios of each to the sum of easily MRS-measurable phosphate metabolites [PCr] + [ATP] + [Pi], while ADP is given in molar units, since it is calculated from the CPK equilibrium. Left panels in A, B, and C indicate representative MRS data. Right panels show plots of work intensity (% maximum ATP turnover rate) as the independent parameter and metabolite concentrations at the end of each work bout are plotted as dependent parameters (on the vertical axes). (Modified from Allen et al., 1997.)... 

Hochachka, P.W. and G.B. McClelland (1997). Cellular metabolic homeostasis during large scale changes in ATP turnover rates in muscles. J. Exp. Biol. 200 381-386. 

These two processes together account for the bulk of the energy savings that allow the very low ATP turnover rates requisite for long-term hypoxia survival. These adjustments are only possible because of ... 

The acute or defense phase of hypoxia tolerance is considered to blend almost imperceptibly into a secondary series of processes in the literature these are variously termed immediate-early gene responses (Webster et al., 1993) or accli-matory expression adjustments (Hochachka and Somero, 1984). As the combined effect of these processes is to reactivate some mRNA translational capacities and probably to consolidate and stabilize the cell at strikingly reduced ATP turnover rates, we refer to these combined processes as a rescue phase for establishing hypoxia tolerance. The rescue phase includes (figure 3.18)... 

Hochachka P.W., and G.O. Matheson (1992). Regulating ATP turnover rates over broad dynamic work ranges in skeletal muscles. J. Appl. Physiol. 73 1697-1703. 

This increased conversion of pyruvate to lactate decreases the pH in areas of the brain that have rapid ATP turnover rates and leads to cellular destruction. 

Intensified silicon intensifier target Rate of ATP turnover Rate of lactate production... 

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