In a muscle fiber, mechanical power output is coupled to ATP splitting. How this

is achieved is not fully understood, although there has been great success in many field endeavours in muscular research such as the structure of the contractile apparatus and its functional correlates [2,3,4,5,6]. Since Huxley’s widely accepted sliding filament theory [7,8], the cross-bridge cycle is of central importance, especially in the functional aspects of contraction. This cycle must contain the reactions of free energy transduction from chemical (ATP splitting reaction) to mechanical energy (actin movement against a load force). From the #click here keyword# overall reaction, contractile efficiency can be obtained by relating mechanical power output to the dissipation function of ATP splitting, where the mechanical power is given by the product of the force exerted by the load and the shortening velocity. Experimental results Inhibitors,research,lifescience,medical show [9,10,11,12], that when efficiency is expressed as a function of v, a curved line with a maximum is obtained. From non-equilibrium thermodynamics (NET, [13]), it is well known that uncoupling is necessary to generate a maximum in efficiency plots (efficiency against reduced force ratio). Thus, to yield such a maximal efficiency, any description of the cross-bridge cycle on a thermodynamic basis must contain an uncoupling mechanism, which Inhibitors,research,lifescience,medical uncouples the transduction

of free energy from ATP splitting to actin movement. To describe the cross-bridge cycle in terms of the new flux equations published recently [1], the cross-bridge Inhibitors,research,lifescience,medical cycle has to be formulated in relation to this formalism, which combines the basics of NET [13,14,15,16] with Michaelis-Menten-like Inhibitors,research,lifescience,medical kinetics of enzyme-catalysed reactions [17]. It will be shown that Hill’s equation describing muscular

performance [18,19] can be easily deduced by applying the new flux equation. When compared with other approaches to the energetics of the cross-bridge cycle, the main particularity of the present work may be the fact that this cycle is connected here to energy metabolism of the muscle fiber, i.e., to ATP producing and consuming reactions. The generation of mechanical energy from the free energy of ATP splitting is treated here as one of the parallel reactions of the sarcosol consuming ATP delivered in fast fibers, mainly from glycogenolysis or glycolysis, respectively. This integration into Adenylyl cyclase the cell’s energy metabolism makes it possible to inspect some variables like ATP and its reaction products and species at high mechanical power output. In addition, concentration changes in metabolites and ions like creatine phosphate, lactate, H+, and Mg2+, are of interest under these conditions. This is achieved by formulating, in particular, the ATP splitting reaction according to Alberty [20] as a function of both [H+] and [Mg2+].