Abstract
It is now appreciated that mitochondrial creatine kinase (CKm) may play an important role in heart high-energy phosphate metabolism and that this isozyme is solubilized in vitro by dilute solutions of Pi. Since an increase in cellular Pi is known to occur with even brief periods of myocardial ischemia, we investigated the relationship between CKm activity and myocardial performance in rabbit hearts subjected to total global ischemia. CKm activity is expressed as a ratio to mitochondrial malate dehydrogenase (MDHm), a stable marker enzyme. A significant decline in this ratio was observed after only 10 min of ischemia, a time prior to changes in total homogenate creatine kinase activity. After 60 min of ischemia, the CKm/MDHm ratio was depressed by more than 70%. Since there was no restoration of activity following 30 min of reperfusion, we correlated changes in enzyme activity to contractile dysfunction following variable periods of total ischemia. The data showed a close correlation between the decline in the CKm/MDHm ratio and the reduction in performance, measured as left ventricular developed pressure. No correlation was observed between State 3 respiratory rates and performance. Using KCl arrest at 27 degrees C or hyperthermic ischemia at 40 degrees C, the CKm/MDHm ratio consistently correlated to the degree of postischemic functional depression, independent of the duration of ischemia. Isoenzyme electrophoresis failed to detect soluble CKm activity in the postischemic supernatant. Therefore, CKm activity appears to be altered rapidly and irreversibly by ischemia. The implications of these observations on the integration of myocardial high-energy phosphate metabolism are discussed.
Highlights
From The Peter Belfer Laboratory for Myocardial Research, $Department of Medicine and the VDepartment of Biological Chemistry, The Johns Hopkins Uniuersity, School of Medicine, Baltimore, Maryland 21205
It is appreciated that mitochondrial creatine tionhas focused on identifyingmitochondrial respiratory kinase (CK,) may play a n important role in heahritgh- defects arising during ischemia that limit the rate of highenergy phosphate metabolism and that thisisozyme is energy phosphate synthesis
Selection of~ i t o c ~ ~ dMr a~rkaerZEnzymes-There is some normal variability in the specific activity of creatine kinase in isolated mitochondrial fractions [26,46].These differences was warmed during ischemia to 40 "C, and pacing increased to 240 probably result from nonmitochondrial protein contaminabeats/min
Summary
T H E PROGRESSIVE LOSS OF ENZYMEACTIVITYDURING IN VIVO ISCHEMIA AND ITS CORRELATIONTODEPRESSED MYOCARDIAL FUNCTION*. The abbreviations used are: CK,, mitochondrial creatine kinase; ing the time when this work was conducted, and author to whom MDH,, mitochondrial malate dehydrogenase; LVDP, left ventricular reprint requests should be addressed at: 538 Carnegie Building, Di- developed pressure; LV dP/dt, the first derivative of the left ventricvision of Cardiology, The JohnsHopkins Hospital, 600 North Wolfe ular pressure curve; EGTA, ethylene glycol bis(S-aminoethyl ether)- Resuspended to a protein concentration of 5.0 mg/ml These data arediscussed from the view that changes in CK, activity, resulting in an alteration of energy transport, may be one of the earliest mitochondrial defects induced by ischemia. They suggest that a number of important bio-. Supernatant solutions were decanted, and thepellets resuspended for the analysis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
