PHOSPHOCREATINE PROTECTS TRANSGENIC MOUSE-LIVER EXPRESSING CREATINE-KINASE FROM HYPOXIA AND ISCHEMIA

Creatine kinase (CK) is normally found at high levels in muscle and br ain and catalyzes the reaction phosphocreatine (PCr) + MgADP + H+ doub le-line arrow pointing left and right creatine (Cr) + MgATP. CK is not normally found at high levels in liver. A line of transgenic mice tha t express high levels of the BB-dimer of CK (CK(B)) in liver has allow ed us to assess the role of CK(B) during periods of low oxygen stress. During 40 min of ischemia of normal perfused livers at 25-degrees-C, ATP levels are depleted, and pH decreases to 6.6. pH recovers to a pre ischemic level after 30 min of reperfusion of normal livers; however, P(i) levels are significantly higher and ATP levels significantly lowe r than preischemic values. In transgenic liver with an initial PCr-to- ATP ratio of 4.5, ATP levels are maintained until PCr is markedly depl eted. pH remains at preischemic levels for 16 min of ischemia of trans genic livers. During this length of ischemia in normal livers, pH has dropped to 6.9. pH, P(i), and ATP levels return to preischemic values within 30 min of reperfusion in transgenic livers containing PCr and C K. During 90 min of hypoxia of normal perfused livers at 37-degrees-C, ATP is depleted. After 15 min of hypoxia of normal livers, there is a significant increase in the release of lactate dehydrogenase (LDH). I n transgenic livers, ATP is maintained, and no increase in LDH release is observed for up to 90 min, depending on the level of PCr before hy poxia. These results demonstrate the role of CK(B) in buffering ATP le vels and regulating intracellular pH during periods of low oxygen stre ss. The presence of PCr and CK can slow the onset of cellular damage i nduced by ischemia and hypoxia in liver.