Characterization of vascular permeability factor/vascular endothelial growth factor receptors on mononuclear phagocytes

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a polypeptide mediator, elaborated by certain tumors and other cell types, that exerts multiple effects on endothelium via interaction with a class of high-affinity binding sites. In this report, the interaction of VPF/VEGF with human mononuclear phagocytes (MPs) is characterized. Radioligand binding studies at 4 degrees C showed the presence of a single class of binding sites, kd approximately 300 to 500 pmol/L (approximately 20 times lower affinity than the high-affinity binding site on endothelial cells [ECs]), the occupancy of which correlated with VPF/VEGF-induced MP migration and expression of tissue factor. These binding results were paralleled by functional experiments which indicated that the same VPF/VEGF preparations were about an order of magnitude less effective in stimulating MP chemotaxis than in inducing EC proliferation. When MPs with surface-bound 125I-VPF/VEGF were warmed to 37 degrees C, endocytosis and degradation occurred. Occupancy of VPF/VEGF binding site resulted in subsequent activation of intracellular signal transduction mechanisms, as shown by an increase in MP intracellular calcium concentration. Cross-linking studies with 125I-VPF/VEGF showed a new high-molecular weight band (corresponding to putative 125I-VPF/VEGF-receptor complex), the appearance of which was blocked by excess unlabeled VPF/VEGF. Consistent with these results, immunoprecipitation of 32PO4-labeled MPs exposed to VPF/VEGF showed a single band of similar mobility, not seen in untreated controls. These results demonstrate that the interaction of VPF/VEGF with MPs, though of lower affinity than that observed with ECs, also results from interaction of the polypeptide with a specific cell-surface protein and leads to activation of intracellular transduction mechanisms.

Generation of early afterdepolarization in mouse ventricular fibers at long cycle length

Early afterdepolarization (EAD) was studied in ventricular fibers of mouse heart. EAD could be occasionally induced under long cycle length of superfusion with Tyrode's solution (containing 3.0 or 5.0 mM KCl) at long cycle length. Three types of EAD were found: a second plateau with a prominence, a single triggered burst and a train of triggered bursts. Take-off potential of the first triggered burst or of the prominence varied from -40 to -60 mV. The triggered bursts in the third type often stopped at -35 to -45 mV level forming a very long second plateau before it completely repolarized. Changing abruptly from a long cycle length to a short one lead to a transient EAD induction. It is suggested that EAD in ventricular fiber in mouse heart shared the characteristics of that in atrial fibers, although it was very difficult to induce and was not very reproducible.

Clinical pathologic profiles of dogs and turkeys with congestive heart failure, either noninduced or induced by rapid ventricular pacing, and turkeys with furazolidone toxicosis

Characteristic alterations in the serum and urine biochemical profiles of Doberman Pinschers with congestive heart failure (CHF) resulting from idiopathic dilated cardiomyopathy were determined. We compared these alterations with those observed in 2 other models of CHF: rate overload induced by rapid ventricular pacing in dogs, and biventricular hypertrophy and dilatation induced in turkey poults by furazolidone toxicosis. Serum and urine biochemical changes in both models of CHF in dogs were mild to moderate in degree, and were moderately consistent. They could be attributed to secondary neurohumoral, hepatic, and renal effects of heart failure. The most marked and consistent changes observed were mildly decreased anion gap that developed, in part, because of decreased serum sodium concentration, moderately increased catecholamine concentrations, moderate lactaciduria, hyposthenuria, and mildly increased urea concentrations and liver enzyme activities. In birds with furazolidone cardiomyopathy, we observed mild increases in serum urate concentration, liver and muscle enzyme activities, but moderately increased sodium concentration with decreased chloride concentration. In the pacing and furazolidone models, in which CHF was rapidly induced, moderate to marked hypoproteinemia was attributable to decreases in albumin and globulin concentrations. Using the avian model we found that the hypoproteinemia could be largely attributed to blood volume expansion, and to a lesser extent, inanition. Development of hypoalbuminemia during rapid ventricular pacing and furazolidone treatment may contribute to the effects of rate overload or drug toxicity in the pathogenesis of CHF, because hypoalbuminemia may contribute to altered hemodynamics and neuroendocrine system activation. Our data indicate that clinical biochemical analysis of serum and urine may be useful for assessing progression of CHF.

Identification of cysteine residues involved in disulfide formation in the inactivation of glutathione transferase P-form by hydrogen peroxide

We previously reported that rat glutathione transferase P-form (GST-P) is inactivated by hydrogen peroxide (H2O2). This involves formation of intra- or intersubunit disulfides, at least three extra bands with molecular masses of 21.5, 18, and 37 kDa being exhibited in addition to the native subunit band of 23.5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions. In the present study, GST-P mutants whose cysteine residues were independently substituted with alanine (C14A, C47A, C101A, and C169A) by site-directed mutagenesis were used to identify the cysteine residues responsible for the disulfide bond formation. C14A and C169A were much more inactivated than native GST-P by 1 mM H2O2, whereas C47A and, especially, C101A appeared insensitive to H2O2. On SDS-PAGE, the 21.5-kDa band was not detected in either C47A or C101A. Hydrogen peroxide treatment of mouse GST II, highly homologous to rat GST-P but possessing glycine instead of cysteine at the 101st residue, did not result in generation of the 21.5-kDa band and was also associated with less inactivation. This band was therefore considered to be due to an intrasubunit disulfide bond between Cys-47 and Cys-101. The 37-kDa band was suggested to be due to the formation of intersubunit disulfide bonds between Cys-47 residues in different subunits. Thus the Cys-47 residue together with Cys-101 may be located in an important region for GSH binding, disulfide bond formation between these residues resulting in steric hindrance.

Construction of a Tn7-lux system for gene expression studies in gram-negative bacteria

A Tn7-lux system was developed for gene expression studies in Gram- bacteria. The plasmids constructed, pHSK728 and pHSK729, have the following features: (1) a promoterless Vibrio fischeri lux operon as a reporter system; (2) multiple cloning sites (MCS) ahead of the lux operon, in opposite orientation for the cloning of promoter fragments; (3) a transcriptional terminator ahead of the MCS and translational stop codons in all reading frames before the translational start of the luxC gene; (4) a streptomycin/spectinomycin-resistance encoding gene as a selection marker; and (5) Tn7 border sequences flanking the above elements, permitting the transposition of lux fusion constructs into bacterial genomes. The system was tested using the Escherichia coli lac promoter as well as the differentially regulated promoters of the avrD gene from Pseudomonas syringae pv. tomato and the pelE gene of Erwinia chrysanthemi EC16. Southern blot analysis showed that all fusion constructs had integrated into the host genomes in a single-copy, site-specific manner. The promoters of the avrD and pelE genes resulted in little or no light production when bacteria were grown in rich culture media, but high levels of induction were observed when the bacteria were grown in plant tissues. These results demonstrated that the Tn7-lux system provided a simple, sensitive assay of promoter activity in Gram- bacteria.

Respiratory chain defect of myocardial mitochondria in idiopathic dilated cardiomyopathy of Doberman pinscher dogs

Idiopathic dilated cardiomyopathy (IDCM) is a primary myocardial disease of unknown cause. We tested the hypothesis that IDCM was associated with a myocardial metabolic defect by determining a comprehensive biochemical profile of metabolite concentrations and enzyme activities for the major metabolic pathways of the myocardium. We used the Doberman pinscher breed as a naturally occurring canine model of IDCM and compared its myocardial profile with that of healthy adult mongrels. Compared with controls, myocardium in IDCM had markedly reduced mitochondrial electron transport activity and myoglobin concentration, in association with acidosis and energy depletion following anoxic challenge: 60% decreased NADH dehydrogenase and 50% decreased ATP synthetase activities; 90% decreased myoglobin concentration; and 30% reduced ATP and 50% increased lactate and proton concentrations. Sarcoplasmic reticulum Ca(2+)-transport ATPase was decreased by 42%. There was a 15% compensatory increase in fatty acid oxidation and Krebs cycle activity. Other biochemical changes were mild by comparison with the mitochondrial defects. We conclude that IDCM is associated with a marked impairment of mitochondrial production of ATP, arising from decreased activity of the mitochondrial electron transport system, including myoglobin. These changes may be secondary to an underlying genetic defect or may indicate a deficiency of the mitochondrial respiratory chain that predisposes this breed to heart failure.

Endothelial monocyte-activating polypeptide II. A novel tumor-derived polypeptide that activates host-response mechanisms

An important means by which tumor cells influence the vasculature is through the production of soluble mediators altering vascular properties. A approximately 22-kDa polypeptide was purified to homogeneity from conditioned medium of murine methylcholanthrene A (meth A) fibrosarcoma cells by ion-exchange chromatography and preparative sodium dodecyl sulfate-polyacryl-amide gel electrophoresis (SDS-PAGE), based on its ability to induce tissue factor procoagulant activity in endothelial cells (ECs). The final product migrated as a broad band on reduced and nonreduced SDS-PAGE and had an unique amino-terminal sequence. This meth A-derived polypeptide modulated EC coagulant properties through the induction of tissue factor, induced monocyte migration and tissue factor expression, and was also chemotactic for granulocytes. Injection of the polypeptide into mouse footpads resulted in an inflammatory response with tissue swelling and polymorphonuclear leukocyte infiltration. The ability of this mediator to activate ECs and monocytes has led us to name it EMAP II (endothelial monocyte-activating polypeptide). EMAP II is distinct from a previously described approximately 40-kDa meth A-derived polypeptide termed EMAP I. Through its potential to activate host effector mechanisms, EMAP II could contribute to the biology of immunogenic tumors, such as the meth A fibrosarcoma.

Specific expression of glutathione S-transferase Pi forms in (pre)neoplastic tissues: their properties and functions

The detection of preneoplastic cells is very important for the analysis of carcinogenic processes and for developing strategies for prevention and treatment of cancer. We have been investigating enzyme alterations occurring during rat chemical hepatocarcinogenesis, especially to find more specific enzyme markers for preneoplastic hepatic lesions. We identified the placental form of glutathione S-transferase (GST-P; GST 7-7) as a new marker enzyme for preneoplastic hepatocytes. We also found human placental form, GST-pi, to be a possible tumor marker for various human tissues except liver. In this article, their properties and possible functions are reviewed on basis of our recent investigations. A peroxisomal enzyme, enoyl CoA hydratase, in also described as a possible negative marker for rat preneoplastic hepatic foci/nodules and hepatomas induced by peroxisome proliferators.

Myocardial myoglobin deficiency in various animal models of congestive heart failure

Myoglobin is known to protect the mechanical function of the heart from hypoxia by acting as a sarcoplasmic oxygen reservoir and shuttle. We postulated a role for myoglobin in the pathogenesis of congestive heart failure. Several models of congestive heart failure were employed to test the hypothesis, including spontaneous inherited dilated cardiomyopathy in Doberman Pinschers, and heart failure produced by rapid ventricular pacing in dogs, volume overload in chickens and furazolidone toxicity in turkeys. Myocardial myoglobin was decreased by approximately 50% for all models (P less than 0.05). In Doberman Pinschers dogs which are predisposed to the development of dilated cardiomyopathy and have mild subclinical depression of cardiac performance, myocardial myoglobin (1.05 +/- 0.22 mg/g) is approximately 50% decreased compared to healthy mongrel dogs (2.15 +/- 0.52 mg/g), approximately twice as much as dobermans with heart failure (0.47 +/- 0.25 mg/g) but similar to the concentration found in dogs paced to heart failure (1.09 +/- 0.34 mg/g). Myocardium from poultry had remarkably decreased myoglobin compared to mammals (34 +/- 4 micrograms/g) with heart failure produced either by furazolidone or salt toxicity causing a further 50% reduction. In the canine models of heart failure, myocardial myoglobin concentration was demonstrated to be correlated with biochemical and physiological indicators of myocardial performance, namely, mitochondrial and sarcoplasmic reticular ATPase activities, and cardiac output, systemic vascular resistance, pulmonary capillary wedge pressure and mean arterial pressure, respectively. Our data implicates a role for myoglobin deficiency in the pathogenesis of congestive heart failure and in the predisposition of doberman pinschers to dilated cardiomyopathy.

Rapid, simple and sensitive microassay for skeletal and cardiac muscle myoglobin and hemoglobin: use in various animals indicates functional role of myohemoproteins

A novel, simple, rapid, sensitive and reproducible microassay is described for determination of myoglobin and hemoglobin content of myocardial and skeletal muscle biopsy specimens from various mammals, birds and fish. As little as 50 mg of tissue is needed and myoglobin concentrations lower than 1 mg% can be detected. Myoglobin and hemoglobin are separated at alkaline pH by ammonium sulfate extraction followed by ultrafiltration. Heme content is determined by absorption of the Soret band when the hemoprotein extract is visibly colored or more sensitively by its peroxidase activity when the extract has low color. The heme reacts with tertiary-butyl hydroperoxide and orthotolidine to generate a blue color. Hemoglobin content is correlated with myoglobin content and is related to aerobic capacity and blood flow to the tissue. Myoglobin content varied over 5 orders of magnitude up to 7 per cent of the weight of tissue, whereas hemoglobin content varied over 2 orders of magnitude up to 6 per cent of tissue weight. Myoglobin content is increased in species with high basal metabolic rate, high physical activity, prolonged diving capacity, fatigue resistance, and red muscle, whereas it is decreased in white muscle, iron-deficient animals, animals with sedentary lifestyles, and in animals and tissues with small fiber diameters such as avian or fish hearts.

Endoglucanase A from Cellulomonas fimi in which the hinge sequence of human IgA1 is substituted for the linker connecting its two domains is hydrolyzed by IgA proteases from Neisseria gonorrhoeae

The hinge in IgA1 and the linker in endoglucanase A (CenA) are quite similar. The IgA1 hinge is 18 amino acids long and contains only proline, threonine and serine. The linker in CenA is 27 amino acids long and contains only proline, threonine and a single serine. IgA proteases from Neisseria gonorrhoeae cleave Pro-Ser and Pro-Thr bonds within the IgA1 hinge sequence, but they do not attack CenA. When the linker sequence of CenA is replaced with the hinge sequence of IgA1, the hybrid polypeptide is susceptible to the N. gonorrhoeae proteases. It is cleaved within the hinge sequence at the same sites as IgA1.

[Amphetamine--induced rage reaction in mice and its mechanism]

Rage reaction was induced in mice by ip amphetamine sulfate (APT) 15 mg/kg. Mice appeared hyperreactive after 6 min and then squeaked and fought each other. These manifestations were most distinct in 15-30 min and subsided after 40-70 min. At 20 degrees C and 25 degrees C, the occurrence of rage reaction was 85.0% and 90.0% respectively. The ED50 of APT for eliciting rage reaction was 11.8 +/- 2.1 mg/kg ip. No significant difference in the induction of rage reaction was observed between male and female mice but ambient temperature affected the occurrence of this reaction. Neuroleptic drugs (chlorpromazine, haloperidol, tardan and clozapine), anxiolytic drugs (diazepam and meprobamate) and reserpine suppressed the rage reaction induced by APT in mice. Phenobarbital and pentobarbital (at sedative doses), atropine, scopolamine, phentolamine and propranolol exerted no influence on APT--induced rage reaction. Amantadine, levodopa and apomorphine at lower doses potentiated the rage inducing effect of APT. Moreover, at higher doses amantadine or levodopa alone also evoked rage reaction similar to that induced by APT. Therefore, it may be deduced that the APT-induced rage reaction results from increased release of dopamine in limbic system and has nothing to do with the simultaneous epinephrine release. The available data indicate that the APT--induced rage reaction in mice deserves to be recommended as an animal model for screening potential neuroleptic drugs. The merits and shortcomings of this new model are discussed.

Myocardial calcium cycling defect in furazolidone cardiomyopathy

We have previously demonstrated that in furazolidone-induced congestive heart failure in turkeys the specific Ca(2+)-ATPase activity of myocardial sarcoplasmic reticulum (SR) is 60% increased in compensation for a 50% depression in net Ca(2+)-sequestration activity. This study tested the hypothesis that SR Ca(2+)-uptake and Ca(2+)-ATPase activities were uncoupled in this cardiomyopathy because of increased Ca(2+)-release channel activity. A novel microassay was used to monitor Ca2+ transport by myocardial homogenates using the fluorescent Ca2+ dye indo 1 to indicate extravesicular ionized Ca2+. The method is applied to cyropreserved biopsy specimens of myocardium and requires only 50 mg tissue. Both SR Ca(2+)-pump and SR Ca(2+)-channel activity were estimated using the channel-inhibitor ruthenium red (RR) and the mitochondrial inhibitor sodium azide. The specificity of the RR inhibition was confirmed using ryanodine. Cardiomyopathy was induced in 2-week-old turkey poults by the addition of 0.07% furazolidone to their feed for 4 weeks. Compared with controls, myocardial maximal Ca(2+)-channel activity relative to maximal Ca(2+)-pump activity was 22% greater and duration of Ca(2+)-channel activity was 100% increased. However, the heart failure birds had 43 and 53% decreases in absolute maximal Ca(2+)-pumping and Ca(2+)-channel activities, respectively. The abnormal Ca(2+)-channel activity resulted in 200% greater time before initiation of net Ca2+ sequestration and 700% greater final myocardial Ca2+ concentrations. For all birds, the Ca(2+)-accumulating activity was highly correlated with Ca(2+)-release activity (all p less than 0.05). These data indicate that in this animal model of congestive heart failure there is defective SR Ca(2+)-channel function resulting in abnormal Ca2+ homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of mild cardiac hypertrophy, induced by volume overload in turkeys, on myocardial sarcoplasmic reticulum calcium-pump and calcium-channel activities and on the creatine kinase system

Recent studies indicate that in animals with marked cardiac hypertrophy, there is depressed function of Ca2+ sequestration by myocardial sarcoplasmic reticulum (SR) because of down regulation of the Ca(2+)-ATPase gene. However, in several animal models we have observed enhancement of myocardial Ca2+ sequestration in response to chronic cardiac stimulation. We tested the hypothesis that in animals with mild cardiac hypertrophy, there is enhanced Ca(2+)-cycling activity by the SR Ca2+ pump and Ca(2+)-release channel. Because creatine kinase activity is consistently decreased in cardiomyopathy, we also determined whether enhanced Ca2+ cycling was accompanied by down regulation or inhibition of the creatine kinase system. Mild cardiac hypertrophy was induced by volume overload; 2% salt was added to the diet of 2-week-old turkey poults for 4 weeks. Compared with age-matched controls, volume overload resulted in 14.3% increase in heart weight and 21.5% increase in heart-to-body weight ratios. The hypertrophied heart had approximately 20% increased activities of the SR Ca2+ pump and the SR Ca2+ channel. Net Ca2+ transport was increased by 16.5%. Compared with controls and in contrast to several other myocardial enzymes, creatine kinase activity was diminished in the hypertrophied hearts by 23% and creatine content was decreased by 8%. Differences between groups were not detected for lactate dehydrogenase, aspartate transaminase, and alanine transaminase. We concluded that an early adaptation of the myocardium undergoing hypertrophy in compensatory response to functional overload is an enhancement of Ca2+ cycling activity by the Ca2+ pump and Ca2+ channel of the SR.(ABSTRACT TRUNCATED AT 250 WORDS)

Deletion of the linker connecting the catalytic and cellulose-binding domains of endoglucanase A (CenA) of Cellulomonas fimi alters its conformation and catalytic activity

The Pro-Thr box is a linker of 23 amino acids ((PT)4T(PT)7) connecting the catalytic domain and the cellulose-binding domain (CBD) of endoglucanase A (CenA) from the bacterium Cellulomonas fimi. Deletion of the Pro-Thr box alters the conformation of CenA by changing the relative orientation of the catalytic domain and the CBD. The tertiary structures of the catalytic domain and the CBD appear to be unchanged. The change in conformation reduces the catalytic efficiency of the enzyme and masks one of two protease-sensitive sites between the domains. The deletion does not affect the adsorption of the enzyme to microcrystalline cellulose, but it does affect its desorption from cellulose. The results suggest that the Pro-Thr box in CenA has an extended, kinked, and rigid conformation.

[Effect of posture on pharyngeal area measured by acoustic reflection technique]

Patients with obstructive sleep apnea (OSA) have a smaller pharyngeal area (PA) and higher compliance than normal subjects. The apnea-hypopnea index (AHI) in OSA patients determined by polysomnographic study was greater in the supine than lateral position. Recently there have been reports of reduction in the PA by the acoustic reflection technique (ART) in the supine position. However, there has been no report on the PA measured by ART in the lateral position which is important in the treatment of OSA. To evaluate differences in the PA with posture changes, we measured the PA in 41 normal subjects (11 males and 30 females) in the sitting, lateral and supine positions by ART. The average PA in the sitting position in the males and females was 3.8 +/- 0.6 cm2, and 3.3 +/- 0.5 cm2, respectively. The average PA in the lateral position in the males and females was 3.5 +/- 0.6 cm2, and 3.1 +/- 0.5 cm2, respectively. The average PA in the supine position in the males and females was 2.9 +/- 0.5 cm2, and 2.7 +/- 0.4 cm2, respectively. PA in the sitting position correlated well with body surface area (BSA). The average PA in both the males and females was significantly smaller in the supine than in the sitting position. The average PA in the lateral position in both males and females was significantly smaller than that in the sitting position and was significantly larger than that in the supine position. Decrease in PA with posture (from sitting to lateral) in the males (9.2 +/- 5.5%) was similar to that in the female (5.7 +/- 5.4%). Decrease in PA with posture (from sitting to supine) was significantly larger in male (24.4 +/- 9.5%) than in female (16.6 +/- 6.8%). We conclude that the decrease of PA in the supine position is ameliorated in the lateral position in normal subjects. Lateral position may be the preferred sleeping position in snoring or OSA patients.

Myocardial Ca-sequestration failure and compensatory increase in Ca-ATPase with congestive cardiomyopathy: kinetic characterization by a homogenate microassay using real-time ratiometric indo-1 spectrofluorometry

A novel, simple, rapid and reproducible microassay is used for kinetic analysis of Ca-sequestration by homogenates of myocardium of turkeys with furazolidone-induced congestive cardiomyopathy. The assay monitors Ca in real-time using dual-emission ratiometric spectrofluorometry and the Ca-indicator dye indo-1. Using this assay and isolated SR studies we make several novel findings regarding the mechanism of SR failure in furazolidone cardiomyopathy. Qualitative differences in Ca-sequestration were not detected between groups. However, compared to controls the furazolidone treatment resulted in: 1) 50% depression in maximal activities (1.54 +/- 0.36 vs 0.73 +/- 0.12 microM/sec); 2) 2-fold increases in post-sequestration concentrations of ionized Ca (79 +/- 23 vs 141 +/- 13 nmol Ca/L homogenate); 3) 2-fold increases in Ca half-life (415 vs 790 msec); and 4) 25% increased passive Ca-binding capacity of homogenates. The Ca-ATPase specific activity of isolated sarcoplasmic reticulum was 60% increased in congestive cardiomyopathy (543 +/- 140 vs 873 +/- 108 nmol ATP hydrolyzed/min/mg membrane protein) although membrane yield was 20% decreased (0.79 +/- 0.09 vs 0.63 +/- 0.03 mg/g heart). The increased ATPase and decreased Ca-uptake activities in combination with the occurrence of 36% cardiac hypertrophy and 19% decreased body weights resulted in estimates of the relative energy cost to the animal for myocardial Ca transport being 5.5-fold increased with cardiomyopathy (20.5 vs 111 nmol ATP hydrolyzed per microM decrease of sarcoplasmic free Ca/kg body weight). These data indicate that congestive cardiomyopathy is associated with markedly increased permeability of sarcoplasmic reticulum to Ca and compensatorily increased Ca-ATPase activity. Accelerated energy consumption due to the increased energy cost of Ca transport and increased time of myocyte activation are predicted to predispose the myocardium to fatigue and irreversible failure.

Cardiac and muscle fatigue due to relative functional overload induced by excessive stimulation, hypersensitive excitation-contraction coupling, or diminished performance capacity correlates with sarcoplasmic reticulum failure

The development of muscle fatigue due to exhaustive exercise is associated with impaired sarcoplasmic reticulum (SR) Ca-transport activity. This study tested the hypothesis that SR failure is a consistent feature of cardiac and skeletal muscle fatigue owing to relative functional overload regardless of the method of induction: excessive stimulation, diminished performance capacity, or excessive excitation-contraction coupling. The Ca-transport activity was determined using three unique models of muscle fatigue: chronic and rapid ventricular pacing in dogs; metabolic inhibition caused by global cardiac ischemia in swine; and the hypermetabolic syndrome of porcine malignant hyperthermia (MH). Both pacing- and ischemia-induced fatigue resulted in reduction of SR Ca-transport ATPase activity: from 275 +/- 58 to 159 +/- 57 nmol.min-1.mg-1 (mU/mg) and from 577 +/- 82 to 177 +/- 133 mU/mg, respectively. Both pacing-induced fatigue and halothane-induced MH resulted in reduction of Ca-sequestration activity of muscle homogenates from 5.95 +/- 2.4 to 3.11 +/- 0.67 nM/s at 300 nM Ca and 38.7 +/- 10.5 to 16.3 +/- 8.0 nM/s at 1500 nM Ca, respectively (all p less than 0.01). The isolated SR Ca-ATPase activity correlated with Ca-sequestration activity of myocardial homogenates (r = 0.76; p less than 0.005). Different models were used to study the relationship of Ca-transport activity with relaxation function, degree of acidosis, and ionized Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)