Dissociation between cellular K+ loss, reduction in repolarization time, and tissue ATP levels during myocardial hypoxia and ischemia

The mechanisms underlying the marked increase in [K+]o in response to ischemia are not fully understood. Accordingly, the present study was performed to assess the contribution of ATP-regulated K+ channels by using simultaneous measurements of cellular K+ efflux, [K+]o, transmembrane action potentials, and tissue ATP, ADP, phosphocreatine, and creatine content in a unique isolated, blood-perfused papillary muscle preparation during hypoxia compared with ischemia. During 15 minutes of hypoxic perfusion (PO2, 6.1 +/- 0.9 mm Hg) with normal [K+]o of 4.1 +/- 0.1 mM, action potential duration (APD) was not altered even though tissue ATP levels decreased markedly from 33.5 +/- 1.8 to 14.7 +/- 2.0 nmol.mg protein-1 (p < 0.01). Net cellular K+ efflux, based on measured differences of [K+] between the venous effluent and the perfusate, was 13.23 +/- 0.79 mumol.g wet wt-1 during hypoxia. In contrast, after 15 minutes of zero-flow ischemia, APD at 80% of repolarization (APD80) decreased by 47% from 171 +/- 5 to 92 +/- 5 msec (p < 0.01), but integrated net cellular K+ efflux over 15 minutes of ischemia was 8.4-fold less (1.57 +/- 0.13 mumol.g wet wt-1) than during hypoxia. Tissue ATP levels, however, decreased by only 35.2% to 21.7 +/- 2.1 nmol.mg protein-1, which was significantly less than that induced by 15 minutes of hypoxia. Perfusion with hypoxic blood containing high [K+]o of 10.3 +/- 0.3 mM resulted in APD shortening similar to that observed during ischemia. Cellular K+ loss, however, was inhibited markedly by high [K+]o perfusion (only 4.51 +/- 0.28 mumol.g wet wt-1). Pretreatment with glibenclamide (5 microM), a drug that has been reported to inhibit ATP-regulated K+ channels and accelerate glycolysis in normoxic tissue, partially inhibited cellular K+ efflux during hypoxic perfusion with normal [K+]o (7.35 +/- 0.71 versus 13.23 +/- 0.79 mumol.g wet wt-1, p < 0.01) but had no significant influence on repolarization time or tissue ATP levels. Although glibenclamide partially prevented action potential shortening induced by hypoxic perfusion in the presence of elevated [K+]o, the proportion of cellular K+ efflux reduced by glibenclamide was less (23%) than that observed with glibenclamide in hypoxic perfusion with normal [K+]o (44%).(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetics of transient pump currents generated by the (H,K)-ATPase after an ATP concentration jump

(H,K)-ATPase containing membranes from hog stomach were attached to black lipid membranes. Currents induced by an ATP concentration jump were recorded and analyzed. A sum of three exponentials (tau 1(-1) approximately 400 sec-1, tau 2(-1) approximately 100 sec-1, tau 3(-1) approximately 10 sec-1; T = 300 K, pH 6, MgCl2 3 mM, no K+) was fitted to the transient signal. The dependence of the resulting time constants and the peak current on electrolyte composition, ATP conversion rate, temperature, and membrane conductivity was recorded. The results are consistent with a reaction scheme similar to that proposed by Albers and Post for the NaK-ATPase. Based on this model the following assignments were made: tau 2 corresponds to ATP binding and exchange with caged ATP. tau 1 describes the phosphorylation reaction E1 x ATP-->E1P. The third, slowest time constant tau 3 is tentatively assigned to the E1P-->E2P transition. This is the first electrogenic step and is accelerated at high pH and by ATP via a low affinity binding site. The second electrogenic step is the transition from E2K to E1H. The E2K<==>E1H equilibrium is influenced by potassium with an apparent K0.5 of 3 mM and by the pH. Low pH and low potassium concentration stabilize the E1 conformation.

Preimplantation alteration of adenine nucleotides in cryopreserved heart valves

To assess the initial metabolic phase of cellular injury from cardiac valve processing, high-energy phosphate concentrations were analyzed in valve leaflets subsequent to critical processing steps. Using a porcine model, valves were processed in a manner identical to human homografts, with 58 randomly assigned to five groups representing distinct preparation phases. Group I (controls) sustained 40 minutes of warm ischemia concluded by liquid nitrogen immersion. Remaining groups similarly endured 40 minutes of ischemia, but were subsequently prepared according to stepwise design: II, warm ischemia + 24 hours of 4 degrees C ischemia; III, warm ischemia + 24 hours of 4 degrees C antibiotic disinfection; IV, warm ischemia + 24 hours at 4 degrees C (without antibiotics) + cryopreservation (-1 degrees C/min cryoprotected freezing); and V, warm ischemia+disinfection+cryopreservation. At each regimen's conclusion leaflet extracts were assayed by high-performance liquid chromatography for high-energy adenine nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate) and catabolites. A 47% and 86% decrease in cellular adenosine triphosphate level was observed in group III and group V leaflets, respectively. The level of total adenine nucleotides was maintained up to cryopreservation; thereafter a 74% decrease was noted. Catabolite analysis confirmed incomplete degradation of adenine nucleotides indicating cellular metabolic resilience throughout standard homograft preparation in valves previously exposed to 40 minutes of warm ischemia.

Studies of adenine nucleotide biochemistry in the Chediak-Higashi syndrome

The Chediak-Higashi syndrome (CHS) is an inherited disorder of humans and of several animal species, characterized by partial albinism, pseudohemophilia, increased susceptibility to disease, and large inclusions in all granule-forming cells. In this study, various parameters of adenine nucleotide biochemistry were examined in beige mouse kidney tissue and in peripheral blood leukocytes from CHS mink. There were no differences in the total protein content, total ATPase activity or the magnesium (Mg2+) ATPase or the sodium-potassium (Na(+)-K+) ATPase activities, the concentrations of ATP, ADP, and AMP, or the adenylate energy charge (AEC) in kidney extracts from beige and normal mice. In studies of leukocytes, there were no differences in the concentrations of ATP, ADP, AMP, and cAMP or the AECs in total leukocyte preparations and in extracts from granulocytes or nongranulocytes. These results can be explained by any one of several hypotheses: no storage pool of adenine nucleotides exists in the tissues examined; or the alleged storage pool is not affected by CHS; or the quantity of nucleotides in the alleged storage pool is too minute to be evaluated by current techniques; or the CHS defect might cause a shift from the storage pool to the metabolic pool.

Biocytin synthetase activity in human milk as assessed by high-performance liquid chromatography

A reversed-phase liquid chromatographic assay for biocytin synthetase activity has been developed. By this method, biocytin synthetase, isolated to homogeneity from human milk, was found to synthetize biocytin from biotin and L-lysine in the presence of ATP and magnesium ion(s). Both ATP and magnesium ion(s) were required for the synthesis of biocytin. Equal molar amounts of ADP and ATP were produced and consumed, respectively, in the course of the production of the same molar amount of biocytin; however, production of AMP was not observed. Biocytin synthetase Michaelis constants were 2.5, 1.8, and 0.11 mM for biotin, L-lysine, and ATP, respectively. Biocytin synthetase from milk was shown to synthesize biocytin in a stoichiometric amount.

Metabolic and electrophysiological changes in rabbit skeletal muscle during ischaemia and reperfusion

OBJECTIVE

To clarify the effects of ischaemia and reperfusion on membrane potential of skeletal muscle in rabbits, and to study its correlation with the energy charge and the lactate content.

DESIGN

Open experimental study.

MATERIAL

20 isolated rabbits' hindlimbs.

INTERVENTIONS

The femoral arteries were cannulated and the limbs amputated at the level of the hip joint. Blood was removed by thorough perfusion with Ringer's solution. Below knee fasciotomies were done, and the whole limbs were immersed in Ringer's solution during periods of ischaemia. Reperfusion was with a modified Krebs' buffer with Dextran T70 saturated with oxygen.

OUTCOME MEASURES

Measurements of membrane potential; ATP, ADP, and AMP concentrations; and lactate concentrations in muscles after 1 (n = 8), 2 (n = 4), 4 (n = 4), or 6 (n = 4) hour periods of ischaemia followed by a 2 hour period of reperfusion compared with those in 4 limbs that were made ischaemic for 8 hours and not reperfused.

RESULTS

During the first hour of ischaemia the membrane potential decreased from -90 mV to -63 mV and the energy charge remained unchanged at 0.9. After 8 hours of ischaemia the membrane potential had decreased to -20 mV, the energy charge was 0.2, and the lactate content had increased by a factor of 12. During reperfusion the membrane potential was restored only in limbs that had been subjected to 1 hour of ischaemia, whereas energy charge was also restored in those subjected to 2 and 4 hours of ischaemia. The lactate content decreased during reperfusion in all limbs.

CONCLUSION

Assessment of membrane potential is more sensitive than that of energy charge as an indicator of recovery of skeletal muscle after a period of ischaemia followed by reperfusion.

ATP depletion is associated with cytotoxicity of a novel lipid regulator in guinea pig adrenocortical cells

A novel lipid regulator (PD132301-2) produces degeneration and necrosis of adrenal fasciculata in guinea pigs. Primary adrenocortical cell cultures from male Hartley guinea pigs were utilized to investigate potential mechanisms of this toxicity. Concentration-dependent loss of viability, measured by neutral red (NR) accumulation or MTT reduction, was observed within 6 hr at concentrations of 0.01 to 10 microM PD132301-2. At 10 microM, NR and MTT indices were 50% of those of control after 6 hr exposure. Maximal decreases in NR and MTT indices to 20% of control values occurred by 24 hr at > or = 1 microM PD132301-2. Adenine nucleotide analysis after PD132301-2 challenge indicated that ATP depletion preceded loss of viability. At 10 microM PD132301-2, ATP levels were 80% of those of control after 30 min and 25% of those of control after 6 hr. Supplementation of glucose-free buffer with 20 mM fructose protected adrenocortical cells from PD132301-2-induced toxicity. Fructose protection was blocked by inhibiting glycolysis with 1 mM sodium fluoride. Pretreatment of cultures with 100 microM metyrapone, an inhibitor of cytochrome P-450, did not block cytotoxicity induced by 10 microM PD132301-2, but did block cytotoxicity of 100 microM o,p'-DDD. In adrenocortical mitochondrial preparations, inhibition of respiration by PD132301-2 was site II-specific. Both state 3 and state 4 respiration were inhibited 50-75% at 1-30 microM PD132301-2. Thus, ATP depletion resulting from direct inhibition of mitochondrial respiration is a critical early event in adrenocortical cytotoxicity of PD132301-2.

Studies on the rapid stimulation of mitochondrial respiration by thyroid hormones

Injection of L-3,5-diiodothyronine (T2) into rats made hypothyroid by 6-n-propyl-2-thiouracil (PTU) increased the respiration rates of subsequently isolated liver mitochondria; this stimulation of respiration by T2 occurred in the presence of cycloheximide and is therefore independent of protein synthesis on cytoplasmic ribosomes. Injection of T3 into PTU-treated rats had a lesser effect than T2 on the respiration rates of subsequently isolated mitochondria; as PTU is an inhibitor of 5'-iodothyronine deiodinases, which convert T3 into T2 in vivo, the rapid stimulation of mitochondrial respiration by T3, which has been shown in a range of systems, may not be due directly to T3 itself, but may be mediated by its deiodination product T2. Injection of T2, or T3, into hypothyroid or euthyroid rats had no effect on the percentage activity of mitochondrial pyruvate hydrogenase assayed 30 min later. The amount of active pyruvate dehydrogenase is regulated by changes in mitochondrial calcium concentration and matrix ATP/ADP ratio; therefore these parameters are not persistently affected by treatment with T3 or T2. In addition, the total amount of pyruvate dehydrogenase present was the same in euthyroid and hypothyroid rats, indicating that the expression of this enzyme is not stringently controlled by thyroid hormone status.

The influence of maternal nicotine exposure on neonatal lung carbohydrate metabolism

The influence of maternal nicotine exposure (1 mg/kg body mass/day) during pregnancy and lactation on energy metabolism of lung tissue of neonatal rats were investigated. The glucose turnover of the lung tissue of the neonatal rats exposed to nicotine via the placenta and mother's milk was 86.4% higher than that of the controls. Glycolysis was however suppressed by 22.7% (P < 0.01). The adenine nucleotide pool (ATP+ADP+AMP) was 32.8% higher for the lungs of the 3 week old neonates exposed to nicotine than that of the control rat lung. After 4 weeks of nicotine withdrawal glycolysis of those animals exposed to nicotine were still inhibited to the same extent than during exposure. The adenine nucleotide pool was 69.95% higher than that of the controls. It is proposed that the inhibition of glycolysis was due to the high ATP/ADP ratio of the lungs of the nicotine exposed rats.

Catalytic properties of Escherichia coli F1-ATPase depleted of endogenous nucleotides

Nucleotide-depleted Escherichia coli F1 was prepared by the procedure of Wise et al. (1983, Biochem. J. 215, 343-350). This enzyme had high rates of steady-state ATPase and GTPase activity. When "unisite" ATP hydrolysis was measured using an F1/ATP concentration ratio of 10, all of the substoichiometric ATP became bound to the high-affinity catalytic site and none became bound to noncatalytic sites. The association rate constant for ATP binding was 7 x 10(5) M-1 s-1 and the KdATP was 7.9 x 10(-10) M, as compared to values of 3.8 x 10(5) M-1 s-1 and 1.9 x 10(-10) M, respectively, in native (i.e., nucleotide-replete) F1. Rate constants for bound ATP hydrolysis, ATP resynthesis, and P(i) release, and the reaction equilibrium constant, were similar in nucleotide-depleted and native F1. Therefore, we conclude that occupancy of the noncatalytic sites is not required for formation of the high-affinity catalytic site of F1 and has no significant effect on unisite catalysis. In further experiments we looked for the occurrence of inhibitory, catalytic-site-bound MgADP in E. coli F1. Such an entity has been reported for chloroplast and mitochondrial F1. However, our experiments gave no indication for inhibitory MgADP in E. coli F1.

Adenosine triphosphate (ATP) concentrations and ATP/adenosine diphosphate ratios in human sperm of normospermic, oligospermic, and asthenospermic specimens and in their swim-up fractions: lack of correlation between ATP parameters and sperm creatine kinase concentrations

The authors had previously found an inverse correlation between per sperm creatine phosphokinase activity and sperm concentrations in men. Because creatine phosphokinase is a key enzyme in sperm energy transport, the possible relationship of sperm creatine phosphokinase activity, sperm adenosine triphosphate (ATP) concentrations, sperm ATP/ADP (adenosine diphosphate) ratios, and computer-aided semen analysis sperm motility parameters were then studied. The ATP concentrations and ATP/ADP ratios, measured by high-pressure liquid chromatography in washed sperm, were similar in normospermic and oligospermic specimens (ATP: 123.1 +/- 21.6 vs. 90.0 +/- 24.5 pmol/10(6) sperm; ATP/ADP: 2.8 +/- 0.4 vs. 2.1 +/- 0.4, N = 32 and 17, mean +/- SEM), and in samples with normal and less than 40% sperm motility (ATP: 96.8 +/- 27.2 vs. 122.2 +/- 19.6 pmol/10(6) sperm; ATP/ADP: 2.4 +/- 0.5 vs. 2.8 +/- 0.4, n = 26 and 23). In the swim-up sperm fractions, which showed improved motility, the ATP concentrations, but not the ATP/ADP ratios, were lower than in the initial semen samples (ATP: 152.9 +/- 28.4 vs. 90.3 +/- 10.6 pmol/10(6) sperm, P less than 0.05; ATP/ADP: 3.3 +/- 0.5 vs. 3.9 +/- 0.7, N = 18 pairs of samples). This is consistent with our previous finding of a lower cytoplasmic content in sperm in swim-up fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine and guanine nucleotide content of Triton-extracted cytoskeletal fractions of nonmuscle cells

Determination of the adenine and guanine nucleotides in Triton X-100-extracted cytoskeletal fractions was utilized to estimate the actin and tubulin content of the assembled cytoskeletons in nonmuscle cells. Results with stable cell lines (i.e., rat pheochromocytoma PC12 and neuroblastoma NB41A3) and with primary cultures (i.e., human foreskin fibroblasts and chick embryonic dorsal root ganglion neurons) exhibited levels of cytoskeletal fraction ADP and GDP consistent with their assembly-induced nucleoside-5'-triphosphatase activities only previously analyzed in vitro. Likewise, estimates of actin and tubulin content fall in the range of values obtained by other experimental approaches. In contrast, analysis of whole cell nucleotides showed high [ATP]/[ADP] and [GTP]/[GDP] ratios, suggesting there is little, if any, contamination of the cytoskeletal nucleotide pool by other cellular nucleotides.

Myocardial adenine nucleotide concentrations and myocardial norepinephrine content in patients with heart failure secondary to idiopathic dilated or ischemic cardiomyopathy

It has been suggested that chronically reduced myocardial adenosine triphosphate (ATP) content causes contractile dysfunction in dilated cardiomyopathy. Because total adenine nucleotides (ATP, adenosine diphosphate and monophosphate) may reflect chronic changes in energy metabolism better than may ATP alone, myocardial ATP, and adenosine diphosphate and monophosphate were determined in endomyocardial biopsy specimens from 19 patients with dilated cardiomyopathy, and decreased left (30 +/- 2%) and right (34 +/- 3%) ventricular ejection fractions, and from 11 patients with ischemic cardiomyopathy (left ventricular ejection fraction 38 +/- 3%), and compared with those from 28 normal control subjects (ejection fraction greater than 55%) to assess myocardial energy metabolism in heart failure. Myocardial norepinephrine was measured simultaneously in the same biopsy specimens to assess if the myocardium studied for adenine nucleotide content was metabolically altered. Myocardial total adenine nucleotides as well as ATP levels in 19 patients with dilated cardiomyopathy (39 +/- 3 and 23 +/- 3 nmol/mg of noncollagen protein, respectively) were unchanged in comparison with those of control subjects (37 +/- 4 and 23 +/- 3, respectively); patients with ischemic cardiomyopathy were not significantly different (30 +/- 3 and 19 +/- 3, respectively). Myocardial norepinephrine in the same biopsy specimens from patients with dilated (5.8 +/- 1.1 pg/micrograms of noncollagen protein) or ischemic (5.7 +/- 1.3) cardiomyopathy was significantly decreased compared with that of normal control subjects (12 +/- 1.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of training on the calf muscle energy metabolism. A 31P-NMR study on four elite downhill skiers challenged with a standardized exercise protocol

This study evaluates the effects of a 6 months' training period on the bioenergetics of the calf muscle of elite athletes by means of phosphorus-31 Nuclear Magnetic Resonance Spectroscopy (31P-NMR). Four downhill skiers, belonging to the Spanish National Team, performed a standardized exercise protocol using their right leg inside a wide-bore 2.35 Tesla magnet. The inorganic phosphate/phosphocreatine (Pi/PC) ratio and intracellular pH (pHi) were measured at steady-state during an exercise protocol composed of 5 work levels between 20% and 80% of the maximum voluntary contraction (MVC), before and after the training period. The measured values, which were markedly scattered at the beginning, regrouped after training. This was caused by a shift towards lower Pi/PC ratios and by a lower pHi acidification in three of the four subjects. This result suggests that 31P-NMR is a good tool to evaluate changes in the muscle aerobic capacity of athletes induced by training.

Evaluation of a procedure for the simultaneous determination of oxidized and reduced pyridine nucleotides and adenylates in organic phenol extracts from mitochondria

An extraction procedure using mixtures of phenol, chloroform, and isoamyl alcohol originally applied to quench mitochondria for determining adenylates proved suitable also for the quantification of reduced and oxidized pyridine nucleotides yielding recoveries of more than 90%. In combination with HPLC, this approach allows the simultaneous determination of NAD+, NADP+, NADH, and NADPH as well as of adenylates within one extract. A comparison of this extraction method with fluorimetric measurements of pyridine nucleotide reduction in intact mitochondria revealed that about 30% of the fluorescence signal in the resting state of liver mitochondria is caused by NADPH.

Determination of concentrations of adenosine and other purines in human term placenta by reversed-phase high-performance liquid chromatography with photodiode-array detection: evidence for pathways of purine metabolism in the placenta

A robust analytical method, using reversed-phase high-performance liquid chromatography with gradient elution and photodiode-array detection, was used to measure six purines and beta-NAD+ in acid-soluble extracts of samples taken from six different regions of human term placenta. Resolution of the analyte peaks in chromatographic profiles of the extracts, and the use of optimized integration, allowed simultaneous quantitation of all seven analytes from a single chromatogram. Peak purity was confirmed via on-line analysis of peak spectra, utilizing the purity parameter treatment of spectral data. Major placental purines were adenosine, inosine, hypoxanthine and adenine. Except for adenine, concentrations of the purines varied by two-fold or more between different regions of each placenta, but concentration ratios, i.e., adenosine/inosine and inosine/hypoxanthine, were similar. The findings indicate that the pathway of ATP breakdown to hypoxanthine in ischemic human term placenta is via adenosine, and that regional differences in placental concentrations of adenosine and its metabolites may result from regional differences in degree of ischemia.

Rapid determination of creatine, phosphocreatine, purine bases and nucleotides (ATP, ADP, AMP, GTP, GDP) in heart biopsies by gradient ion-pair reversed-phase liquid chromatography

A simple binary solvent method has been developed for the simultaneous determination of creatine (Cr), phosphocreatine (PCr), ATP, ADP, AMP, GTP, GDP, IMP, NAD, inosine, adenosine, hypoxanthine and xanthine. This allows separation of the most important nucleotides present in myocardial biopsies as, for example, in studies using 31P NMR spectroscopy. In NMR spectra ATP and PCr are the only visible high-energy phosphates, therefore the status of other nucleotides and bases cannot be determined. The nucleotides, AMP degradation products, PCr and Cr in pig and rat heart muscle were resolved with 35 mM K2HPO4, 6 mM tetrabutylammonium hydrogensulfate buffer, pH 6.0, and a binary acetonitrile gradient on medium-bore, 250 mm or 125 mm x 3.9-4.6 mm I.D. steel octadecyl-bonded (C18) columns at a flow-rate of 1.5 or 1.0 ml/min. This method, optimized for use with older high-performance liquid chromatography pumps (100 microliters displacement heads), resolves the major porcine and rat myocardial nucleotides and degradation products within 22 min. The amounts found in normoxic porcine muscle are: Cr 9.21 +/- 0.75; hypoxanthine 1.40 +/- 0.14; PCr 7.20 +/- 1.2; IMP 1.34 +/- 0.13; beta NAD 1.82 +/- 0.23; AMP 0.10 +/- 0.04; GDP 0.05 +/- 0.02; ADP 1.23 +/- 0.09; GTP 0.19 +/- 0.01; ATP 4.45 +/- 0.32 mumol/g wet weight. The method, incorporating adenosine tetraphosphate as an internal standard, allows the documentation of changes in both the high-energy phosphates and their degradation products in a single analysis of myocardial samples as small as 200 micrograms (wet weight).

Significant quantities of endogenous GDP and ADP are present on catalytic sites of the F1-ATPase isolated from M. lysodeikticus in the absence of added nucleotides

The F1-ATPase from Micrococcus lysodeikticus is isolated in the absence of exogenous nucleotides. After removing loosely bound nucleotides from the isolated enzyme by gel permeation chromatography, analysis for tightly bound nucleotides revealed in 14 experiments 0.4 +/- 0.1 mol ADP, 0.5 +/- 0.2 mol GDP, and 0.8 +/- 0.2 mol ATP per mol of F1. Incubation of the isolated enzyme with Mg2+ or Ca2+ did not alter the endogenous nucleotide composition of the enzyme, indicating that endogenous ATP is not bound to a catalytic site. Incubation of the enzyme with P(i) decreased the amount of tightly bound ADP and GDP but did not effect the ATP content. Hydrolysis of MgATP in the presence of sulfite raised the tightly bound ADP and lowered tightly bound GDP on the enzyme. In the reciprocal experiment, hydrolysis of MgGTP in the presence of sulfite raised tightly bound GDP and lowered tightly bound ADP. Turnover did not affect the content of tightly bound ATP on the enzyme. These results suggest that endogenous ADP and GDP are bound to exchangeable catalytic sites, whereas endogenous ATP is bound to noncatalytic sites which do not exchange. The presence of endogenous GDP on catalytic sites of isolated F1 suggests that the F0F1-ATP synthase of M. lysodeikticus might synthesize both GTP and ATP under physiological conditions. In support of this hypothesis, we have found that plasma membrane vesicles derived from M. lysodeikticus synthesize [32P]GTP from [32P]P(i) using malate as electron donor for oxidative phosphorylation.

A mixture of nucleosides and a nucleotide alters hepatic energy metabolism 24 hours after hepatectomy in rabbits

The effect of administering a nucleoside-nucleotide mixture on hepatic energy metabolism was evaluated at 24 h after hepatectomy in rabbits that had had 70% of their livers removed. After hepatectomy, animals were administered continuous intravenous infusion of 2 mL/(kg body wt-h) of 9 g/L NaCl (Group S), 5.99 mmol/L nucleoside-nucleotide mixture (Group N1) or 11.98 mmol/L nucleoside-nucleotide mixture (Group N2). At 24 h after hepatectomy, the hepatic adenylate energy charge in Group S (0.83 +/- 0.01, mean +/- SEM) was significantly lower than that before hepatectomy (0.90 +/- 0.01). By contrast, the values in Groups N1 and N2 after hepatectomy (0.74 +/- 0.04 and 0.73 +/- 0.04, respectively) were significantly lower than that in Group S. The hepatic mitochondrial phosphorylation rate before hepatectomy was 46.40 +/- 4.88 nmol ATP/(mg mitochondrial protein-min). After hepatectomy, significantly greater values were observed in Groups N1 and N2 (69.53 +/- 7.20 and 63.31 +/- 6.11, respectively), yet those values were less than observed in Group S (109.14 +/- 4.80). These results suggest that the nucleoside-nucleotide mixture suppressed the enhancement of hepatic mitochondrial phosphorylative activity at a time when hepatic adenylate energy charge is compromised. Such enhancement is needed to compensate for the increased energy expenditure due to surgical intervention.

Verapamil reverses glucose intolerance in preexisting chronic renal failure: studies on mechanisms

Glucose-induced insulin secretion is impaired in chronic renal failure (CRF), and this abnormality is due to the elevation of cytosolic calcium [Ca2+]i and other derangements in pancreatic islet metabolism. Verapamil given to rats from day 1 of CRF prevented the rise in [Ca2+]i of islets and the impairment in insulin secretion. However, it is not known whether verapamil can reverse the abnormalities of islet function and metabolism in animals with preexisting renal failure. Such a documentation has important clinical implications for the treatment of carbohydrate intolerance in patients with CRF. The present study examined this question. After 6 weeks of CRF, rats were randomized into two subgroups and maintained for additional 6 weeks. One subgroup received intraperitoneal injections of verapamil (0.1 micrograms/kg body weight twice daily) and the other received vehicle only. At the time of randomization, there were no significant differences between the two subgroups in their body weight, plasma levels of calcium, phosphorus and creatinine, serum parathyroid hormone and creatinine clearance. Similarly, at the time of sacrifice (12 weeks), there were no significant differences in these parameters except for a modestly lower plasma level of creatinine and modestly higher creatinine clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine nucleotide concentrations and energy charge in muscle of chronic haemodialysis patients

Adenine nucleotide concentrations and energy charge ratios were measured in muscle samples collected during transplant surgery of 7 patients suffering from chronic renal failure and undergoing haemodialysis. The energy charge ratio of 0.75 in the muscle of transplant patients was significantly lower (p less than 0.01) than that of 0.89 found in muscle from controls. The lower energy charge ratio and increased concentrations of adenosine diphosphate and adenosine monophosphate may contribute to the patients' reduced exercise ability and their poor metabolic state.

Small bowel tissue high-energy phosphate alterations during hypothermic storage using different protecting solutions

Since posttransplant function is closely related to energy status after the storage period, the aim of our study was to determine high-energy phosphates in rat small bowels after 21 h of simple ischemic cold storage using different storage solutions. We compared Eurocollins-solution, Bretschneiders-HTK-solution and a modified University of Wisconsin-solution. After flushing the small bowel both intravascularly and intraluminally with the protecting solution, segments of rat small bowel were stored in the same solution at 4 degrees C for 21 h. Determination of high-energy phosphates by high-performance liquid chromatography were done at indicated times. We found that small bowel stored in Eurocollins-solution produced the best graft viability after 21 h of cold storage by maintaining a sufficient level of high-energy phosphates. The high ATP levels were produced by the pronounced anaerobic glycolysis which was facilitated by the high concentration of glucose in the Eurocollins-solution.

Cerebral energy metabolism in guinea pig fetuses during development

During development fetal arterial oxygen tension falls, whereas cerebral oxygen consumption rises due to an increase in cerebral metabolism. To compensate for this increase in oxygen consumption, blood flow and therefore oxygen delivery to the cerebrum rises. To determine whether during development oxygen delivery to the cerebrum meets cerebral oxygen consumption, we measured the concentrations of high-energy phosphates and glycolytic intermediates in the cerebral cortex of fetal guinea pigs at different gestational ages. During development there was no change in the concentrations of adenosine triphosphate, creatine phosphate, adenosine monophosphate, and lactate. However, cerebral concentrations of adenosine diphosphate increased and those of glucose decreased. Our results suggest that the increase in fetal cerebral oxygen delivery during development meets cerebral oxygen consumption with increasing gestational age. We speculate that the measured rise in the concentrations of adenosine diphosphate may accelerate glycolysis during development and therefore may cause a rise in both cerebral blood flow to maintain oxygen delivery.

Determination of cytosolic ADP and AMP concentrations and the free energy of ATP hydrolysis in human muscle and brain tissues with 31P NMR spectroscopy

Based on experimentally determined concentrations of PCr, Pi, ATP, and H+, the ADP and AMP concentrations and the free energy for the ATP hydrolysis in normal human brain and muscle were calculated assuming that the creatine kinase- and the myokinase-catalyzed reactions were in equilibrium, accounting for changes in pH and free Mg2+ ion concentration.