Fatemeh Savabi

Interaction of creatine kinase and adenylate kinase systems in muscle cells.

Elsewhere in this book the important role of creatine kinase and its metabolites in high energy phosphate metabolism and transport in muscle cells has been reviewed. The emphasis of this review article is mainly on the compartmentalized catalytic activity of adenylate kinase in relation to creatine kinase isoenzymes, and other enzymes of energy production and utilization processes in muscle cells. At present the role of adenylate kinase is considered simply to equilibrate the stores of adenine nucleotides. Recent studies by us and others, however, suggest an entirely new view of the metabolic importance of adenylate kinase in muscle function. This view offers a closer interaction between adenylate kinase and creatine kinase, in the process of energy production (at mitochondrial and glycolytic sites), and energy utilization (at myofibrillar sites and perhaps other sites such as sarcoplasmic reticular, sarcolemmal membrane, etc.), thus being an integral part of the high energy phosphate transport system.

Mitochondrial creatine phosphokinase deficiency in diabetic rat heart.

The role of the mitochondrial end of the phosphocreatine energy shuttle was studied in the streptozotocin diabetic rat heart. Diabetic rats had 45 +/- 5% lower body weight and yielded 46 +/- 6% less mitochondria gm of protein than normals. Diabetic heart mitochondria had 32 +/- 7% lower creatine phosphokinase (CPK) activity and 59 +/- 10% lower oxygen consumption rate than normal heart mitochondria. Creatine (25 mM) did not stimulate oxygen uptake by diabetic heart although control (normal) heart mitochondria were stimulated. Inadequate mitochondrial energy production in the form of phosphocreatine could result in lower energy delivery to the myofibrillar contraction sites and might be an important factor in diabetic cardiomyopathy and weight loss.

Alteration of the phosphocreatine energy shuttle components in diabetic rat heart

Considering the important role of the phosphocreatine energy shuttle in contractile function of the heart we decided to study the different components of this shuttle in STZ-induced diabetic rat heart with a known diabetic related cardiomyopathy. Diabetes produced a gradual decline in total CK activity, reaching a maximum of 35-40% decrease after 4 weeks of diabetes, in both atria and ventricles. All of the CK isoenzymes including the mitochondrial CK (CKm) were reduced but to a different extent in these two tissues. The percentage reduction in diabetic ventricles was BB greater than MB greater than CKm greater than MM and in atria was CKm greater than BB greater than MB greater than MM. A major difference between atrium and ventricle was the greater loss of CKm in diabetic atria than diabetic ventricle (75% in atria vs 32% in ventricle). The B subunit seemed to be the one that was affected the most followed by CKm isoenzyme and then the M subunit. The bound myofibrillar CK isoenzyme, expressed as units of activity/mg of myofibrillar protein, was not affected by 4 weeks of diabetes. The high energy phosphates were also reduced in diabetic heart with a greater reduction in phosphocreatine (43-45%) and a smaller change in ATP (27%). Mitochondrial oxidative phosphorylation with alpha-ketoglutarate was reduced (55%) in diabetic heart, whereas, there was no difference when succinate was used as substrate. These changes were reversible by 4 weeks of insulin treatment. The loss of CKm, phosphocreatine and the reduction in mitochondrial oxidative phosphorylation, could result in an inefficient phosphocreatine energy shuttle which could contribute to the cardiac functional defects associated with diabetes.

Kinetic properties and functional role of creatine phosphokinase in glycerinated muscle fibers--further evidence for compartmentation.

The following phenomena were observed when relative contraction and relaxation effects of ATP and creatine phosphate (CP) were studied in rabbit psoas muscle glycerinated fiber bundles containing native creatine phosphokinase (CPK) and ATPase activities: (1) nucleotide was absolutely necessary for contraction; (2) in the presence of a small amount of ADP (250 microM), physiological concentration of CP (10 mM) produced faster and stronger contraction and faster, more complete, relaxation than equimolar or higher concentrations of ATP; (3) if the nucleotide was in the form of ATP, the nucleotide Km for contraction was about 1.5 mM; (4) if the nucleotide was in the form of ADP, the nucleotide Km for contraction at physiological concentration of CP (10 mM) was 0.076 to 1.18 mM depending upon the order of addition of ADP and CP; (5) the apparent Km for CP for contraction was 2.67 mM independent of sequence of addition of ADP and CP.

Magnetic resonance imaging and quantitative analysis of intracranial cystic lesions: surgical implication.

The authors evaluated a series of proven intracranial cystic lesions prospectively. The relative signal intensities of these lesions on both T1- and T2-weighted sequences were correlated with the composition and viscosity of the cystic contents. Specimens were collected from 51 patients by cyst aspiration or at the time of surgery. Once a specimen was obtained, it was immediately sent for quantitative analysis of proteins, cholesterol, triglyceride, calcium, and blood by-products. In 30 patients, the cystic lesion was hypointense on T1 and hyperintense on T2 relative to white matter. The cystic content in this group of patients was a watery fluid that could be easily aspirated. In another 14 patients, the cystic lesion was either isointense or hyperintense on T1 and hyperintense on T2-weighted sequences. In this group of patients, the cystic contents were mild to moderately viscous and a wide bore needle or cannula was required for aspiration. In the remaining seven patients, the cystic contents were hyperintense (n = 4), isointense (n = 2), or hypointense (n = 1) on T1 but all were markedly hypointense on T2-weighted sequences. The contents of the cystic lesions in these seven patients ranged from pastelike to solid and had to be removed surgically. This study concludes that the observed T1- and T2-weighted signal intensities can predict the relative viscosity and the composition of intracranial cystic contents. This information is found to be quite useful in planning surgery and using appropriate instrumentation in the management of intracranial cystic masses.

Effect of food restriction on the phosphocreatine energy shuttle components in rat heart

Malnutrition has been associated with changes in cardiac metabolism and performance. We have previously reported a diabetic-type cardiomyopathy associated with chronic food restriction and weight loss. Because the creatine-phosphocreatine-creatine kinase system is important in the contractile process, we studied the components of this system in rats fed a food-restricted diet (33% of control animal intake). After 4 weeks of food restriction, total creatine kinase (CK) activities were reduced by 28% in ventricles and by 38% in atria. The CK isoenzymes in the heart were not equally affected. The BB isoenzyme was decreased by 77% and 78%, the MB isoenzyme by 45% and 43%, the MM isoenzyme by 22% and 19% and CKmito by 16% and 15% in ventricles and atria, respectively. In contrast, brain CK activity which is predominantly the BB isoenzyme, was slightly higher in the food-restricted than in control rats. Further studies on ventricular tissue from food-restricted rats revealed a 27% decline in myofibrillar CR activity and a 58% decline in myofibrillar ATPase activity. Phosphocreatine and creatine concentrations were not changed by food restriction, however, ATP was decreased by 23% in ventricles from rats on the restricted diet. Cardiac mitochondrial oxidative phosphorylation was also impaired. State 3 respiration with alpha-ketoglutarate was reduced 20% in the food-restricted heart. These changes are compared to those which we previously observed in the diabetic rat heart and the significance of these findings is discussed.

Three-step preparation and purification of phosphorus-33-labeled creatine phosphate of high specific activity

Rabbit heart mitochondria were used as a source of enzymes for the synthesis of phosphorus-labeled creatine phosphate. This method is based on the coupled reaction between mitochondrial oxidative phosphorylation and mitochondrial-bound creatine kinase. It is possible to convert more than 90% of the inorganic phosphate (Pi) to creatine phosphate. The method used only small amounts of adenine nucleotides which led to a product with only slight nucleotide contamination. This could be removed by activated charcoal extraction. For further purification, a method for the removal of residual Pi is described.

Magnetic Resonance Imaging and Quantitative Analysis of Intracranial Cystic Lesions

ABSTRACTTHE AUTHORS EVALUATED a series of proven intracranial cystic lesions prospectively. The relative signal intensities of these lesions on both T1- and T2-weighted sequences were correlated with the composition and viscosity of the cystic contents. Specimens were collected from 51 patients by c

Altered functional activity and anoxic tolerance in diabetic rat isolated atria

Functional activities of isolated atria from 4-week diabetic rats and their anoxic tolerance and recovery were compared to those of control rats. The present study showed a two-fold increase in maximum developed contraction force (CF), the rate of force development, and the rate of relaxation in isolated atria from diabetic rat heart over that of the control. The rate of the sinoatrial node was lower in the diabetic. However, this lower rate was not responsible for higher CF of the diabetic isolated atria since the twofold difference was still present when both diabetic and control atria were electrically paced at identical rates. Although the high energy phosphate content of the diabetic isolated atria was lower than that of control (50% lower phosphocreatine and 15% lower ATP), diabetic atria exhibited improved short term anoxic tolerance and recovery compared to that of the control. The recovery from long term anoxia, however, was better in control than in diabetic atria, considering the higher original CF in diabetic atria. The present observations are compatible with better ischemic tolerance and higher basal force development observed by some investigators on diabetic isolated heart preparations but not with impaired contractility reported by others. Possible mechanisms responsible for the observed changes are discussed.

Postanoxic recovery of spontaneously beating isolated atria: pH related role of adenylate kinase.

The functional activity, adenine nucleotides, and creatine phosphate content of spontaneously beating isolated rabbit atria were measured prior to anoxia, after 1 hr anoxia, and at the end of 1 hr reoxygenation at pH 6.7 and 7.2 During anoxia at pH 7.2 there was 13.3% loss of adenine nucleotides pool, 35.2% loss of ATP, 36.2% increase in ADP, 200% increase in AMP, and a decrease to 8.8% of CP assayed to the beating atria in oxygen. At pH 6.7 there was almost the same decrease in CP, about 10% decrease in ATP, no change in total adenine nucleotides, no change in AMP and a higher increase in ADP (88.7%). The postanoxic recovery was much more complete when the pH was 6.7 during anoxia, and the first 40 min of reoxygenation. The extent of recovery of functional activity correlated well with the level of ATP in all cases not CP. Since the adenylate kinase and ATPase activity both decrease at acidic pH, their combined diminution would tend to preserve the adenine nucleotide pool and thus the better recovery at pH 6.7, because of a decrease in energy demand and unavailability of AMP for the degradation process. This study also supports the notion of compartmented adenine nucleotides connected by the creatine phosphate-creatine energy shuttle.