ON THE STATE OF CREATINE IN HEART MUSCLE

Abstract

Studies on the rates of incorporation of creatine-1-C14 into the separated and analytically measured creatine phosphate and so-called "free" creatine fractions in perfused isolated rabbit hearts have shown that the specific activity of the creatine phosphate fraction rises more rapidly than does that of the "free" fraction. Upon washout the specific activity of the "free" fraction falls three times as rapidly as does that of the creatine phosphate fraction. Cardiac arrest slows but does not stop the incorporation of label in the creatine phosphate. The creatine phosphate breakdown and resynthesis is therefore not exclusively contraction-linked. The kinetics of movement of label are incompatible with the assumption of a homogeneous "free" creatine pool. Reasons are presented for favoring the view that the fraction conventionally measured as free creatine consists of at least 2 chemical entitles, one bound in such a way as to be freed during acid extraction. The actual concentration of free creatine in the cell need not be higher than that in the extracellular fluid to account for known facts, if one assumes the existence of a creatine complex which comprises most of the analytically determined "free" creatine.