ALTERATIONS IN THE MYOCARDIAL CREATINE-KINASE SYSTEM DURING CHRONIC ANEMIC HYPOXIA

Objective. The aim was to use a model of chronic anaemia in the rat, i n which there is an increase in cardiac mitochondrial creatine kinase activity (mito-CK) per mitochondrion, to test the hypothesis that crea tine stimulated respiration in saponin skinned fibres is correlated wi th mito-CK activity. In order to discuss the altered regulation of mit ochondrial respiratory rate in the context of other metabolic alterati ons, steady state metabolite concentrations and maximum extracted acti vities of regulatory enzymes in glycolysis were also investigated. Met hods: Weanling male Wistar Albino rats were randomly distributed into two experimental groups. One group received a powdered diet deficient in iron (5-7 mg iron.kg-1) while the second group was placed on a stan dard laboratory chow diet (109 mg iron.kg-1) for 4-8 weeks. Results: T otal cardiac creatine kinase activity was unchanged in anaemic rats; h owever, a 25% increase in nascent or functional mito-CK activity per m itochondrion was detected [0.969(SEM 0.005), control group and 1.203(0 .040), anaemic group, p < 0.001]. The sensitivity of creatine (40 mM c reatine, V(Cr)) and ADP (0.1 mM ADP, V0.1) stimulated respiration, as a percentage of maximum respiratory rate (2.0 mM ADP, V2.0), was incre ased by 48% and 52% respectively in the anaemic skinned cardiac fibres . An increase in basal respiration with glutamate and malate as substr ates was detected in the anaemic group compared to the control group, at 6.77(0.74) v 4.58(0.35) ng O.min-1.mg-1 dry weight (p < 0.025). Cyt osolic ATP was decreased in isolated perfused hearts from anaemic anim als, at 35.18(3.11) mumol.g-1 dry weight in control hearts versus 23.6 6(1.42) in anaemic hearts (p < 0.01). A significant increase in myocar dial glycolytic capacity was detected in anaemic cardiac tissue, as ev idenced by a 20% increase in phosphofructokinase activity (p<0.01). Ph osphorylase activity was unaltered in anaemic hearts, indicating that the increased glucose requirement originated from exogenous sources. L actate dehydrogenase (LDH) was increased by 30% in anaemic hearts (p<0 .001). The LDH isozyme profile was shifted in favour of lactate and NA D+ production, thus supporting anaerobic glycolysis. Conclusions: In s upport of the phosphocreatine circuit model, the increased mito-CK per mitochondrion in the anaemic skinned fibre preparation was associated with an increase in creatine stimulated respiration. In addition, the sensitivity of mitochondrial respiratory rate to ADP and the maximum glycolytic capacity were increased in anaemic fibres. Although the net effect of these changes in metabolic capacity and regulation on in vi vo high energy phosphate flux is unknown, it is likely that they are a daptive alterations that compensate for the lower steady state cytosol ic nucleotide concentration.