The Mechanochemistry of Cardiac Muscle

Abstract

The utilization of creatine phosphate (CP) and adenosine triphosphate (ATP) was studied in the iodoacetate (IAA) and nitrogen (N 2 )-treated cat papillary muscle. Under these conditions the net production of ATP does not occur, and the net utilization of ATP is reflected in a fall in CP concentration. The rate of energy utilization of the IAA-N 2 -treated cat papillary muscle resting without tension was 0.68 mole CP/g/min. This rate was increased to 1.07 umole/g/min when muscles were passively stretched with 2 g of tension. In a series of isometrically contracting muscles CP utilization was found to be proportional to the number of activations and the summated contractile element work. These rates of CP utilization were 0.083 /Amole/g/activation and 0.0059 tumole/g-cm of work. The calculated mechanochemical coupling efficiency was 33 %.

The effect of physical training upon the mechanical and metabolic performance of the rat heart

“…This confirms the fundamental observation that fiber shortening is less costly in terms of energy consumption than is tension (23).…”

“…In order to accomplish this accurate determination of tension, contractility and extent of fiber shortening should be available (22,23). Ventricular volumes were not determined, and therefore, these variables cannot be accurately quantitated.…”

Influence of the Thyroid State on the Intrinsic Contractile Properties and Energy Stores of the Myocardium*

“…The recent development of methods for detailed and quantitative analysis of mechanical characteristics of isolated cat papillary muscle (8), removed from the nervous, humoral, and metabolic influences that exist in vivo, and the ability to compare the function of muscles obtained from different groups of animals (9), permit critical examination of these problems. In addition, although interpretation of many previous studies of myocardial high energy phosphate stores in altered thyroid states (10)(11)(12)(13)(14) was limited by the extreme lability of these energy stores, recent modifications of biopsy and analytic techniques have made possible the accurate assessment of these stores in vivo (15,16).…”

“…Myocardial biopsies for high energy phosphate determinations were stored in liquid nitrogen. On the day of assay, each tissue was pulverized at -50'C as previously described (16) and perchloric acid extracts were prepared. Creatine phosphate (CP) and inorganic phosphate (Pi) were determined by the phosphomolybdate method of Fiske and Subbarow (19) as modified by Furchgott and De Gubareff (15).…”

“…Creatine concentrations were measured by the a-napthol-diacetyl method of Ennor and Rosenberg (20,21), and adenosine triphosphate (ATP) by a modification of the firefly luminescence method of Strehler and McElroy (22). Modifications of these procedures have been described previously in detail (16). To avoid possible errors involved in weighing small tissues in the frozen state, we calculated sample weights by the determination of creatine concentration in two separately obtained samples of the right ventricle and the creatine content of the biopsy sample as previously described (16).…”