Alterations in the myocardial creatine kinase system during chronic anaemic hypoxia

The aim was to use a model of chronic anaemia in the rat, in which there is an increase in cardiac mitochondrial creatine kinase activity (mito-CK) per mitochondrion, to test the hypothesis that creatine stimulated respiration in saponin skinned fibres is correlated with mito-CK activity. In order to discuss the altered regulation of mitochondrial respiratory rate in the context of other metabolic alterations, steady state metabolite concentrations and maximum extracted activities of regulatory enzymes in glycolysis were also investigated.

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 standard laboratory chow diet (109 mg iron.kg-1) for 4-8 weeks.

Total cardiac creatine kinase activity was unchanged in anaemic rats; however, a 25% increase in nascent or functional mito-CK activity per mitochondrion 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 creatine, VCr) and ADP (0.1 mM ADP, V0.1) stimulated respiration, as a percentage of maximum respiratory rate (2.0 mM ADP, V2.0), was increased by 48% and 52% respectively in the anaemic skinned cardiac fibres. An increase in basal respiration with glutamate and malate as substrates 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 x mg-1 dry weight (p < 0.025). Cytosolic ATP was decreased in isolated perfused hearts from anaemic animals, at 35.18(3.11) mumol.g-1 dry weight in control hearts versus 23.66(1.42) in anaemic hearts (p < 0.01). A significant increase in myocardial glycolytic capacity was detected in anaemic cardiac tissue, as evidenced by a 20% increase in phosphofructokinase activity (p < 0.01). Phosphorylase activity was unaltered in anaemic hearts, indicating that the increased glucose requirement originated from exogenous sources. Lactate dehydrogenase (LDH) was increased by 30% in anaemic hearts (p < 0.001). The LDH isozyme profile was shifted in favour of lactate and NAD+ production, thus supporting anaerobic glycolysis.

In support 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 vivo high energy phosphate flux is unknown, it is likely that they are adaptive alterations that compensate for the lower steady state cytosolic nucleotide concentration.