Effects of elevation of phosphocreatine on force and metabolism in rabbit aorta

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Abstract
Rings of rabbit thoracic aorta were incubated in 40 mM creatine; both intracellular free creatine (Cr) and phosphocreatine (PCr) content increased 300% in 4 h, whereas tissue ATP content and PCr-to-Cr ratio remained constant. Exogenous Cr was taken up and metabolized by creatine kinase; the newly formed PCr was available for tissue metabolism. Compared with control tissue, muscle rings with markedly increased Cr and PCr content showed no difference in either the rate of contraction with norepinephrine or the amplitude of contraction. ATP production rates, computed from mitochondrial and glycolytic metabolism during rest and during maintained contractions, were similar for creatine-loaded and control rings. Under conditions where muscle was developing force, creatine-loaded rings showed a threefold larger decrease in PCr content than untreated rings but no difference in the decrease in PCr/Cr. A similar pattern of PCr depletion was seen when creatine-loaded or untreated NE-contracted muscle was exposed to hypoxia plus zero-glucose medium. In addition, loaded rings showed smaller rates of efflux of lactate than did unloaded rings when exposed to hypoxia in normal glucose medium.