CREATINE-KINASE, ENERGY-RICH PHOSPHATES AND ENERGY-METABOLISM IN HEART-MUSCLE OF DIFFERENT VERTEBRATES

Maximal activities of creatine kinase, pyruvate kinase and cytochrome oxidase and total concentrations of creatine and phosphorylated adenyl ates were measured in cardiac muscle of hagfish, eight teleost species , frog, turtle, pigeon and rat. The ratio of creatine kinase to cytoch rome oxidase with cytochrome oxidase as a rough estimate of aerobic ca pacity and cellular ''energy turnover'', was increased in myocardia of hagfish, turtle and crucian carp. These myocardia are likely to be fr equently exposed to oxygen deficiency. In agreement with this, they po ssess a high relative glycolytic capacity as indicated by a high pyruv ate kinase/cytochrome oxidase ratio. The creatine kinase/cytochrome ox idase ratio for the other myocardia varied within a factor of 2, excep t the value for cod myocardium which was below the others. Total creat ine varied among species and was high in active species such as herrin g, pigeon and rat but also high in crucian carp. The variation in tota l concentration of phosphorylated adenylates was considerably less tha n the variation in total creatine. The high creatine kinase/cytochrome oxidase ratio in myocardia likely to be challenged by hypoxia may rep resent an enhanced efficiency for both ''spatial'' and ''temporal'' bu ffering of phosphorylated adenylates to attenuate the impact of a depr essed energy liberation. As to the differences in total creatine, this factor influences not only the cellular energy distribution but possi bly also contractility via an effect on the free phosphate level.