Phosphocreatine pathway for energy transport: ADP diffusion and cardiomyopathy.

Chemically skinned (by treatment with saponin, 40 micrograms/ml) isolated cardiomyocytes were used to study the intracellular diffusion of ADP and creatine (Cr). Stimulation of respiration was studied in these cardiomyocytes without intact sarcolemma and in isolated heart mitochondrial by addition of ADP and Cr in the presence of 0.2 mM ATP (via mitochondrial creatine kinase reaction: Cr + MgATP = MgADP + PCr). The Michaelis constant (Km) for Cr was similar in both cases, 5.67 +/- 0.11 (SD) mM in skinned myocytes and 6.9 +/- 0.2 mM in mitochondria, showing that there is no significant restriction to the diffusion of this substrate. However, the apparent Km for external ADP increased from 17.6 +/- 1.0 microM for mitochondria to 250 +/- 38 microM for skinned cardiomyocytes, showing decreased diffusivity of ADP as a result of binding to cellular structures. In the presence of 25 mM Cr, the Km for ADP for myocytes decreased to 35.6 +/- 5.6 microM due to the coupling of the creatine kinase and oxidative phosphorylation reactions. Provision of substrate for the creatine kinase reaction amplified the weak ADP signal in the regulation of respiration. The activity of the mitochondrial creatine kinase was decreased by a factor of two in cardiomyopathic hamsters and human hearts and was associated with a twofold decrease in creatine-stimulated respiration. These data show a potentially key role of mitochondrial creatine kinase in the regulation of cellular respiration and the possible importance of changes in its activity for the functional disturbances of the cardiomyopathic heart.

Protection of ischemic myocardium by exogenous phosphocreatine. II. Clinical, ultrastructural, and biochemical evaluations.

In valve replacement operations on 78 patients with acquired heart disease, the efficiency of phosphocreatine in intraoperative protection of ischemic myocardium was evaluated by clinical, morphologic, and biochemical methods. Phosphocreatine (8 to 10 mmol/L) in a blood cardioplegic solution was used in operations on 41 patients; in the control group (37 patients) standard blood cardioplegia was used. In the group with phosphocreatine treatment we observed more rapid recovery of hemodynamics after release of the aortic cross-clamp, a decreased frequency of fibrillation, and more frequent restoration of sinus rhythm even if there were sinus rhythm disturbances before aortic cross-clamping. Analysis of the biopsy samples taken from the right ventricle showed protection of the sarcolemma against ischemic damage afforded by phosphocreatine and complete preservation of high-energy phosphates. The results obtained confirm the conclusion made by Robinson, Braimbridge, and Hearse (J Thorac Cardiovasc Surg 1984; 87:190-200) that phosphocreatine is an effective additional cardioprotective agent when used in cardioplegic solutions.