Cardioprotection by ischemic preconditioning preserves mitochondrial function and functional coupling between adenine nucleotide translocase and creatine kinase.

M. N. Laclau, S. Boudina, J. B. Thambo, L. Tariosse, G. Gouverneur, S. Bonoron-Adèle, V. A. Saks, K. D. Garlid and P. Dos Santos. Cardioprotection by Ischemic Preconditioning Preserves Mitochondrial Function and Functional Coupling Between Adenine Nucleotide Translocase and Creatine Kinase. Journal of Molecular and Cellular Cardiology (2001) 33, 947-956. This study investigates the effect of ischemic preconditioning on mitochondrial function, including functional coupling between the adenine nucleotide translocase and mitochondrial creatine kinase, which is among the first reactions to be altered in ischemia. Three groups of Langendorff-perfused rat hearts were studied: a control group, a group subjected to 30 min ischemia followed by 15 min reperfusion, and a group subjected to ischemic preconditioning prior to 30 min ischemia and 15 min reperfusion. Ischemic preconditioning significantly delayed the onset and amplitude of contracture during ischemia, decreased enzymatic release, and improved the recovery of heart contractile function after reperfusion. Mitochondrial function was assessed in permeabilized skinned fibers. The protective effect of preconditioning was associated with preservation of mitochondrial function, as evidenced by maintenance of the high K(1/2)for ADP in regulation of mitochondrial respiration and V(max)of respiration, the near absence of respiratory stimulation by exogenous cytochrome c, and preservation of functional coupling between mitochondrial creatine kinase and adenine nucleotide translocase. These data suggest that ischemic preconditioning preserves the structure-function of the intermembrane space, perhaps by opening the mitochondrial ATP-sensitive K(+)channel. The consequence is preservation of energy transfer processes from mitochondria to ATP-utilizing sites in the cytosol. Both of these factors may contribute to cardioprotection and better functional recovery of preconditioned hearts.

Cell swelling and glycogen metabolism in hepatocytes from fasted rats.

Cell swelling is known to increase net glycogen production from glucose in hepatocytes from fasted rats by activating glycogen synthase. Since both active glycogen synthase and phosphorylase are present in hepatocytes, suppression of flux through phosphorylase may also contribute to the net increase in glycogen synthesis by cell swelling. We have developed an isotopic procedure to estimate the fluxes through glycogen synthase and phosphorylase in intact hepatocytes and we have examined the effect of cell swelling on both enzyme fluxes. The following observations were made. (1) Hypotonic or glutamine-induced cell swelling increased net glycogen production by activating flux through glycogen synthase with little effect on phosphorylase flux. Proline, previously shown to increase glycogen synthesis more than could be accounted for by its ability to cause cell swelling, increased flux through glycogen synthase and inhibited phosphorylase flux. (2) Incorporation of [14C]glucose into glycogen preceded complete mixing of [14C]glucose with the intracellular pool of UDPglucose. It is concluded that cell swelling affects glycogen synthase only and that UDPglucose is compartmentalized.