Colon capsule endoscopy for colonic surveillance.

AIM: Resources used in surveillance colonoscopies are taking up an increasing proportion of colonoscopy capacity. Colon capsule endoscopy (CCE) is a promising technique for noninvasive investigation of the colon. We aimed to investigate CCE as a possible filter in colonic surveillance with the primary outcome of reducing the number of colonoscopies. METHOD: Patients scheduled for follow-up colonoscopy were subjected to a primary CCE and only supplemental conventional endoscopy if significant pathology was detected or if the CCE examination was incomplete. Significant pathology was defined as more than two small polyps, or one polyp greater than 9 mm or any polyp in patients with hereditary nonpolyposis colorectal cancer. Supplemental endoscopy was carried out to the extent needed to resect the detected polyps and investigate the parts of the colon that were not sufficiently visualized by the capsule. RESULTS: A total of 180 patients were included. Seventy-seven patients (43%) had a complete CCE with no significant findings. A complete colonoscopy was carried out in 67 patients (37%) and 36 patients (20%) underwent a sigmoidoscopy. In the 103 patients undergoing endoscopy, 59 (57%) had no adenomas detected, 33 (32%) had 'low-risk' adenomas and 11 (11%) had 'high-risk' adenomas. CONCLUSION: The introduction of CCE as filter test in colonic surveillance reduced colonoscopies by 43%, but this implies that untreated polyps are left behind and is not cost-effective. The CCE completion rate must be improved.

Rapid switch-off of the human myosin heavy chain IIX gene after heavy load muscle contractions is sustained for at least four days.

Long-term heavy load contractions decrease the relative amount of the myosin heavy chain (MHC) IIX isoform in human skeletal muscle, but the timing of the down-regulation in the short term is unknown. Untrained subjects performed two resistance bouts, in two consecutive days, with one leg, the other leg serving as a control (age 24±1, n=5). Muscle biopsies were obtained in both legs before, immediately after, and 24, 54, and 96 hours after exercise. Serial cryosection analysis combined immunohistochemistry and ATPase histochemistry with In Situ hybridization to identify the distribution of MHC isoforms and their corresponding transcripts, enabling identification of transitional fibers. Fibers positive solely for MHC IIX mRNA decreased in the exercised leg throughout the study period. At 96 hours post-exercise, no fibers solely expressed MHC IIX mRNA. In contrast, the number of fibers expressing MHC IIA mRNA increased throughout the study period. The percentage of fibers expressing mRNA for MHC I was unchanged in both legs at all time points. Pronounced depletion of glycogen in the MHC IIX fibers of the exercised leg verifies that the type IIX fibers were active during the heavy load contractions. Major mismatch between MHC at the mRNA and protein levels was only found in the fibers of the exercised leg. These data provide unequivocal in situ evidence of an immediate shutdown of the MHC IIX gene after resistance exercise. A further novel finding was that the silencing of the MHC IIX gene is sustained at least 4 days after removal of the stimulus.

Development of a tail vein transection bleeding model in fully anaesthetized haemophilia A mice - characterization of two novel FVIII molecules.

INTRODUCTION: The tail tip bleeding model and the tail vein transection survival model in mice are important tools for assessment of in vivo effect in haemostasis research. While the tail vein transection model exhibits the best sensitivity to pharmacological intervention it uses death or near-death as endpoint which is fully avoided in the tail tip bleeding model. AIM: The aim of this study was to develop a new tail bleeding model maintaining the sensitivity of the previous survival model but avoiding death/near-death as endpoint. METHODS: Combining the two existing tail bleeding models we developed an optimized version of the survival model with full anaesthetic coverage and short duration of experiments. Using this model, we characterized the effect of turoctocog alfa, a B-domain truncated FVIII molecule (NovoEight(®) ), as well as the prolonged half-life version of the same molecule (turoctocog alfa pegol, N8-GP). RESULTS: Data showed that the model was sensitive to clinically relevant doses of both turoctocog alfa as well as N8-GP when dosed for 'on demand' treatment. The model also correctly identified a longer duration of effect for N8-GP compared with turoctocog alfa. Moreover, the model allowed the use of mice of both genders and was reproducible over time. CONCLUSION: The optimized tail vein transection bleeding model is sensitive to standard as well as half-life prolonged FVIII molecules and should be a valuable alternative to both the tail tip bleeding model, enhancing sensitivity to pharmacological intervention, as well as to the previously used tail vein transection survival model, avoiding death or near-death as endpoint.

Identifying developmental toxicity pathways for a subset of ToxCast chemicals using human embryonic stem cells and metabolomics.

Metabolomics analysis was performed on the supernatant of human embryonic stem (hES) cell cultures exposed to a blinded subset of 11 chemicals selected from the chemical library of EPA's ToxCast™ chemical screening and prioritization research project. Metabolites from hES cultures were evaluated for known and novel signatures that may be indicative of developmental toxicity. Significant fold changes in endogenous metabolites were detected for 83 putatively annotated mass features in response to the subset of ToxCast chemicals. The annotations were mapped to specific human metabolic pathways. This revealed strong effects on pathways for nicotinate and nicotinamide metabolism, pantothenate and CoA biosynthesis, glutathione metabolism, and arginine and proline metabolism pathways. Predictivity for adverse outcomes in mammalian prenatal developmental toxicity studies used ToxRefDB and other sources of information, including Stemina Biomarker Discovery's predictive DevTox® model trained on 23 pharmaceutical agents of known developmental toxicity and differing potency. The model initially predicted developmental toxicity from the blinded ToxCast compounds in concordance with animal data with 73% accuracy. Retraining the model with data from the unblinded test compounds at one concentration level increased the predictive accuracy for the remaining concentrations to 83%. These preliminary results on a 11-chemical subset of the ToxCast chemical library indicate that metabolomics analysis of the hES secretome provides information valuable for predictive modeling and mechanistic understanding of mammalian developmental toxicity.

Pharmacokinetics, pharmacodynamics and safety of recombinant canine FVIIa in a study dosing one haemophilia A and one haemostatically normal dog.

Recombinant human FVIIa (rhFVIIa) corrects the coagulopathy in hemophilia A and B as well as FVII deficiency. This is also the case in dogs until canine anti-human FVIIa antibodies develop (~2 weeks). Recombinant canine factor VIIa (rcFVIIa), successfully over-expressed by gene transfer in haemophilia dogs, has provided long-term haemostasis (>2 years). However, pharmacokinetics (PK), pharmacodynamics (PD) and safety of rcFVIIa after pharmacological administration have not been reported. We therefore wanted to explore the safety, PK and PD of rcFVIIa in dogs. A pilot study was set up to evaluate the safety as well as PK and PD of rcFVIIa after a single intravenous dose of 270 µg kg(-1) to one HA and one haemostatically normal dog and to directly compare rcFVIIa with rhFVIIa in these two dogs. Single doses of rcFVIIa and rhFVIIa were well tolerated. No adverse events were observed. Pharmacokinetic characteristics including half-life (FVIIa activity: 1.2-1.8 h; FVIIa antigen 2.8-3.7 h) and clearance were comparable for rcFVIIa and rhFVIIa. Kaolin-activated thromboelastography approached normal in the HA dog with the improvement being most pronounced after rcFVIIa. This study provided the first evidence that administering rcFVIIa intravenously is feasible, safe, well tolerated and efficacious in correcting the haemophilic coagulopathy in canine HA and that rcFVIIa exhibits pharmacokinetic characteristics comparable to rhFVIIa in haemophilic and haemostatically competent dogs. This strengthens the hypothesis that rcFVIIa can be administered to dogs to mimic the administration of rhFVIIa to humans.

The PARIS score can reliably predict 7-day all-cause mortality for both acute medical and surgical patients: an international validation study.

BACKGROUND: We believe errors in the risk assessment of acutely ill patients occur because only vital signs without concurrent functional capacity are considered. We, therefore, developed the PARIS risk score based on blood pressure, age, respiratory rate, loss of independence and oxygen saturation. AIM: Validation of the PARIS score in four independent cohorts from three countries. METHODS: Retrospective cohort study of acutely ill patients admitted to hospitals in Denmark, Ireland and Uganda. Vital signs and functional capacity (registered as ability to stand or walk or get into bed unaided) was recorded upon arrival. Patients were followed up for 7 days (Denmark and Ireland) or until discharge (Uganda) and mortality recorded. The discriminatory power (ability to identify patients at increased risk) was determined using area under the receiver operating characteristics curve (AUROC) and calibration (precision) using Hosmer-Lemeshow goodness of fit test. RESULTS: Out of 14 447 patients, 327 (2.3%) died within 7 days: median age was 59 (39-75) years and 7458 (51.8%) were female. Seven-day mortality increased from 0.3% with a score of 0-26.7% with a score of 5. The score's AUROC as 0.833 [95% confidence interval (95% CI) 0.811-0.856], 0.817 (95% CI 0.792-0.842) and 0.894 (95% CI 0.813-0.974) for all patients, medical patients and surgical patients, respectively. However, except for surgical patients, calibration of the score was poor. CONCLUSION: The PARIS score can identify both high and low risk acutely admitted medical and surgical patients, but calibration was poor for medical patients.

Abrogating fibrinolysis does not improve bleeding or rFVIIa/rFVIII treatment in a non-mucosal venous injury model in haemophilic rodents.

Essentials The efficacy of systemic antifibrinolytics for hemophilic non-mucosal bleeding is undetermined. The effect of systemically inhibiting fibrinolysis in hemophilic mice and rats was explored. Neither bleeding nor the response to factor treatment was improved after inhibiting fibrinolysis. The non-mucosal bleeding phenotype in hemophilia A appears largely unaffected by fibrinolysis. SUMMARY: Background Fibrinolysis may exacerbate bleeding in patients with hemophilia A (HA). Accordingly, antifibrinolytics have been used to help maintain hemostatic control. Although antifibrinolytic drugs have been proven to be effective in the treatment of mucosal bleeds in the oral cavity, their efficacy in non-mucosal tissues remain an open question of significant clinical interest. Objective To determine whether inhibiting fibrinolysis improves the outcome in non-mucosal hemophilic tail vein transection (TVT) bleeding models, and to determine whether a standard ex vivo clotting/fibrinolysis assay can be used as a predictive surrogate for in vivo efficacy. Methods A highly sensitive TVT model was employed in hemophilic rodents with a suppressed fibrinolytic system to examine the effect of inhibiting fibrinolysis on bleeding in non-mucosal tissue. In mice, induced and congenital hemophilia models were combined with fibrinolytic attenuation achieved either genetically or pharmacologically (tranexamic acid [TXA]). In hemophilic rats, tail bleeding was followed by whole blood rotational thromboelastometry evaluation of the same animals to gauge the predictive value of such assays. Results The beneficial effect of systemic TXA therapy observed ex vivo could not be confirmed in vivo in hemophilic rats. Furthermore, neither intravenously administered TXA nor congenital knockout of the fibrinolytic genes encoding plasminogen or tissue-type plasminogen activator markedly improved the TVT bleeding phenotype or response to factor therapy in hemophilic mice. Conclusions The findings here suggest that inhibition of fibrinolysis is not effective in limiting the TVT bleeding phenotype of HA rodents in non-mucosal tissues.

Teratogen-induced eye defects mediated by p53-dependent apoptosis.

BACKGROUND: Many birth defects are believed to involve gene-environment interactions, although the mechanisms involved are poorly understood. Apoptosis is a common effect of many kinds of environmental stresses on the developing embryo; therefore, mechanisms of teratogenesis may be approached within the context of the cell death program. The p53 tumor suppressor gene encodes a transcription factor which functions as a critical regulator of apoptosis in response to environmental stress. RESULTS: To investigate the relationship between p53-dependent apoptosis and teratogenesis, we subjected day 8 mouse embryos with different p53 gene backgrounds to a genotoxic stress, 2-chloro-2'-deoxyadenosine. Treatment rapidly stimulated nuclear p53 accumulation and triggered apoptosis in some (head-fold) but not other (primitive heart) developing structures. Induced cell death was p53 gene-dose dependent, as shown by the intermediate sensitivity of 4-5 somite stage embryos bearing only a single effective p53 allele and the lack of sensitivity of p53-null mutants. Abnormal development was manifested as eye defects by day 11, particularly lens agenesis. Overall the incidences of these defects at term were 73.3% for p53 wild-type fetuses, 52.5% for heterozygous mutants, and 2.2% for p53-null mutants. Statistical analysis indicated that the interaction between teratogen and genotype was highly significant (P < or = 0.001) for cell death on day 8 and eye defects on day 17. CONCLUSIONS: We conclude that teratogen induction of p53-dependent apoptosis in the developing embryo is positively coupled to the determination of congenital eye defects.

Insights into thymic purine metabolism and adenosine deaminase deficiency revealed by transgenic mice overexpressing ecto-5'-nucleotidase (CD73).

The adenosine producing enzyme ecto-5'-nucleotidase (5'-NT) is not normally expressed during thymocyte development until the medullary stage. To determine whether earlier expression would lead to adenosine accumulation and/or be deleterious for thymocyte maturation, thymic purine metabolism, and T cell differentiation were studied in lckNT transgenic mice overexpressing 5'-NT in cortical thymocytes under the control of the lck proximal promoter. In spite of a 100-fold elevation in thymic 5'-NT activity, transgenic adenosine levels were unchanged and T cell immunity was normal. Inosine, the product of adenosine deamination, was elevated more than twofold, however, indicating that adenosine deaminase (ADA) can prevent the accumulation of adenosine, even with a dramatic increase in 5'-NT activity, and demonstrating the availability of 5'-NT substrates in the thymus for the first time. Thymic adenosine concentrations of mice treated with the ADA inhibitor 2'-deoxycoformycin (dCF) were elevated over 30-fold, suggesting that high ADA activity, rather than an absence of 5'-NT, is mainly responsible for low thymic adenosine levels. The adenosine concentrations in dCF-treated mice are sufficient to cause adenosine receptor-mediated thymocyte apoptosis in vitro, suggesting that adenosine accumulation could play a role in ADA-deficient severe combined immunodeficiency.

Programming microphysiological systems for children's health protection.

Microphysiological systems (MPS) and computer simulation models that recapitulate the underlying biology and toxicology of critical developmental transitions are emerging tools for developmental effects assessment of drugs/chemicals. Opportunities and challenges exist for their application to alternative, more public health relevant and efficient chemical toxicity testing methods. This is especially pertinent to children's health research and the evaluation of complex embryological and reproductive impacts of drug/chemical exposure. Scaling these technologies to higher throughput is a key challenge and drives the need for in silico models for quantitative prediction of developmental toxicity to inform safety assessments. One example is cellular agent-based models, constructed from extant embryology, that produce data useful to simulate critical developmental transitions and thereby predict phenotypic consequences of disruption in silico. Biologically inspired MPS models built from human induced pluripotent stem (iPS)-derived cells and synthetic matrices that recapitulate organ-specific physiologies and native tissue architectures are providing exciting new research opportunities to advance the assessment of developmental toxicity and offer the possibility of deriving a full 'human on a chip' system, or a 'Homunculus.' Impact statement This 'commentary' summarizes research needs and opportunities for engineered MPS models for developmental and reproductive toxicity testing. Emerging concepts can be taken forward to a virtual tissue modeling framework for assessing chemical (and non-chemical) stressors on human development. These models will advance children's health research, both basic and translational and new ways to evaluate complex embryological and reproductive impacts of drug and chemical exposures to inform safety assessments.

Expression of tissue factor in canine mammary tumours and correlation with grade, stage and markers of haemostasis and inflammation.

Tissue factor (TF) expression in human cancers has been associated with a procoagulant state and facilitation of metastasis. This study was conducted in order to evaluate if TF was expressed in canine mammary tumours. Forty epithelial mammary tumours from 28 dogs were included. TF expression of the tumours was evaluated by immunohistochemistry using a polyclonal antibody against recombinant canine TF. In addition, thromboelastography, haemostatic and inflammatory parameters were evaluated in the patients. TF was recognized in 44% of benign and 58% of malignant tumours. TF localized to the cytoplasmic membrane of neoplastic luminal epithelial cells and/or diffusely in the cytoplasm. No association was found between TF expression and stage or grade of disease. A significant association between TF expression and antithrombin and plasminogen was found, and extensive TF expression was seen in a lymph node metastasis classified as anaplastic mammary carcinoma from a dog with concomitant disseminated intravascular coagulation (DIC).

Altered expression of mitochondrial 16S ribosomal RNA in p53-deficient mouse embryos revealed by differential display.

Inactivation of the tumor suppressor p53 is associated with neural tube defects and altered teratogenicity in early embryos. To gain insight into the function of p53 during early embryogenesis, RNA profiles of wild-type p53(+/+) and p53(-/-) null mutant mouse embryos were compared at the head-fold stage (day 8 post coitum) using HPLC-based mRNA differential display. The results of this screen revealed a deficiency of mitochondrial 16S ribosomal RNA in p53(-/-) embryos. RT-PCR showed abnormalities in 16S rRNA levels relative to some representative nuclear (COIV, beta-actin) and mitochondrial (COIII) transcripts in p53(-/-) embryos, and that 16S rRNA expression increased with development of p53(+/+) embryos during neurulation. Embryos that lack p53 also displayed weakened cytochrome c oxidase staining and reduced ATP content. During neurulation, the mouse embryo switches from an anaerobic (glycolytic) to an aerobic (oxidative) metabolism. The preliminary results of the present study suggest that p53 may be involved, directly or indirectly, in this transition.

Bcl-2 relieves deoxyadenylate stress and suppresses apoptosis in pre-B leukemia cells.

The influence of bcl-2 activity on 2'-deoxyadenosine-induced apoptosis was investigated in 697 human pre-B leukemia cells stably transfected with expression plasmid pHeBo-BCL-2alpha (697/BCL2 cells). Apoptosis was induced by the 2'-deoxyadenosine analogue, 2-chloro-2'-deoxyadenosine (Cl-dA), with the concentration for apoptosis in one-half of the cells at 24 hours (LD(50)) being 10 microM for 697 cells and 120 microM for 697/Bcl 2 cells. There was a strong positive correlation between Cl-dATP levels and apoptotic index (coefficient of determination, r(2)=0.95; P=0.027). When 697 cell and 697/Bcl 2 cell lines were treated with 5 microM Cl-dA, Cl-dATP did not significantly accumulate in the latter. The Cl-dATP/dATP ratio was 0.03 in Cl-dA treated 697/Bcl 2 cells but nearly 6 in treated 697 cells. Bcl 2 overproduction also suppressed the accumulation of dAMP, dADP and dATP in cells exposed to 2'-deoxyadenosine in the presence of pentostatin to abrogate the pronounced inversion of ATP/dATP pools associated with 2'-deoxyadenosine exposure. These results suggest that one consequence of bcl-2 activity is suppression of 2'-deoxyadenosine phosphorylation and elevation in the apoptotic target cells. Relief from deoxyadenylate stress imbalances implies a novel upstream site of bcl-2 activity.

Predictive value of soluble haemoglobin scavenger receptor CD163 serum levels for survival in verified tuberculosis patients.

Pre-treatment serum levels of sCD163 were measured in a cohort of 236 suspected tuberculosis (TB) cases from Guinea-Bissau, with a median follow-up period of 3.3 years (range 0-6.4 years). In 113 cases, the diagnosis of TB was verified by positive sputum microscopy and/or culture. Among the verified TB cases, a decreased survival rate was found in 27 patients with sCD163 levels above the upper reference limit (3.95 microg/mL). The difference in survival was significant during TB treatment (log rank, p<0.02) and after long-term follow-up (log rank, p<0.001). The decrease in survival rate during TB treatment remained significant in a multivariate Cox model controlling for human immunodeficiency virus (HIV) status, age and gender, with a mortality increase of 1.19 (95% CI, 1.04-1.36) per microg of sCD163, and a hazard ratio (HR) for sCD163 levels above the upper reference limit of 4.18 (95% CI, 1.06-16.4). The difference was not significant after excluding patients with concomitant HIV-1 and HIV-2 infection in Kaplan-Meier analyses (log rank, p 0.11). In contrast, the difference in survival remained significant in Kaplan-Meier analyses after long-term follow-up, even after excluding patients with concomitant HIV-1 and HIV-2 infection (log rank, p 0.002). In the Cox model, the mortality increase per microg of sCD163 was 1.27 (95% CI, 1.14-1.40), with an HR for elevated sCD163 levels of 2.85 (95% CI, 1.44-5.63). The HRs for concomitant HIV-1 and HIV-2 infection were 6.92 (95% CI, 3.28-14.58) and 2.48 (95% CI, 1.09-5.67), respectively. Thus, sCD163 levels appeared to be an independent predictor of survival in verified TB patients.

Consequences of crown shortening canine teeth in Greenland sled dogs.

OBJECTIVES: To evaluate the consequences of crown shortening, focusing on the prevalence of pulp exposure and periapical pathology in Greenland sled dogs that had had their canine crowns shortened at an early age. METHODS: Five cadaver heads and 54 sled dogs underwent an oral examination for dental fractures and pulp exposure of canines. All canines were radiographed and evaluated for periapical pathology. RESULTS: The prevalence of canine pulp exposure in 12 (5 heads and 7 dogs) crown shortened dogs was 91 · 7%, and 21 · 3% in 47 not-crown shortened dogs. A significant (P < 0 · 001) risk of pulp exposure of the canines in the crown shortened group compared to the not-crown shortened group was seen with a relative risk of 4 · 3 on a dog basis and a relative risk of 12 · 2 on a tooth basis. In dogs with pulp exposure of canines (n = 51) the prevalence of periapical pathology was 82 · 4%, but only 0 · 8% in dogs without pulp exposure (n = 133) resulting in a significant (relative risk, 109 · 5; P < 0 · 001) risk of periapical pathology in teeth with pulp exposure compared to teeth without pulp exposure. CLINICAL SIGNIFICANCE: The high risk of periapical pathology observed in teeth with pulp exposure confirms that these teeth should not be neglected in affected dogs.

Physical activity enhances metabolic fitness independently of cardiorespiratory fitness in marathon runners.

High levels of cardiovascular fitness (CRF) and physical activity (PA) are associated with decreased mortality and risk to develop metabolic diseases. The independent contributions of CRF and PA to metabolic disease risk factors are unknown. We tested the hypothesis that runners who run consistently >50 km/wk and/or >2 marathons/yr for the last 5 years have superior metabolic fitness compared to matched sedentary subjects (CRF, age, gender, and BMI). Case-control recruitment of 31 pairs of runner-sedentary subjects identified 10 matched pairs with similar VO2max (mL/min/kg) (similar-VO2max). The similar-VO2max group was compared with a group of age, gender, and BMI matched pairs who had the largest difference in VO2max (different-VO2max). Primary outcomes that defined metabolic fitness including insulin response to an oral glucose tolerance test, fasting lipids, and fasting insulin were superior in runners versus sedentary controls despite similar VO2max. Furthermore, performance (velocity at VO2max, running economy), improved exercise metabolism (lactate threshold), and skeletal muscle levels of mitochondrial proteins were superior in runners versus sedentary controls with similar VO2max. In conclusion subjects with a high amount of PA have more positive metabolic health parameters independent of CRF. PA is thus a good marker against metabolic diseases.

Murine ecto-5'-nucleotidase (CD73): cDNA cloning and tissue distribution.

The murine cDNA, encoding the purine catabolic enzyme, ecto-5'-nucleotidase (NT), was cloned and the tissue-specific distribution of both the mRNA and enzyme activity was examined. Starting with kidney RNA and primers based on the known rat sequence, reverse transcriptase-polymerase chain reaction (RT-PCR) was utilized to obtain the complete sequence for the translated portion of the murine cDNA. Murine NT is 94% identical to human NT at the amino acid (aa) level and 86% identical at the nucleotide (nt) level. NT enzyme assays revealed greater than tenfold more NT activity in mature vs. immature murine T- and B-lymphocytes. A similar increase in NT activity was also found when the pre-B-cell line, 70Z/3, was induced to produce surface kappa light chains with lipopolysaccharide (LPS) and gamma-interferon (gamma-IFN). Thus, culture systems in which murine lymphocytes mature may be useful for examining the mechanisms of NT gene regulation, as well as the function of NT in the immune system. In tissues, enzyme activity varied over 30-fold, from the lowest levels in skeletal muscle, thymus and spleen to highest in placenta, kidney and forestomach. Levels of mRNA, as determined by RNase protection assay, showed increased NT expression in the early gestation site, as compared to non-pregnant uterus, and in day-19.5 placenta, as compared to day-13 chorioallantoic placenta. Messenger RNA levels were in general proportional to enzyme activity, except in the lung and glandular stomach where mRNA levels were higher than expected, based on enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the Na(+)-K+ pump activity and estimation of the reserve capacity in intact rat peritoneal mast cells.

Evidence is provided that regulation of the Na(+)-K+ pump activity in rat peritoneal mast cells occurs mainly through stimulation of the pump from inside the plasma membrane by sodium. It is demonstrated that there is a large reserve capacity for the exchange of intracellular sodium with extracellular potassium in these cells. The maximal pump activity was estimated to be 3230 pmol/10(6) cells per min and Km for extracellular potassium was 1.5 mM.

Effect of ouabain, digoxin and digitoxigenin on potassium uptake and histamine release from rat peritoneal mast cells.

Rat peritoneal mast cells were used to study the effects of digitalis glycosides on potassium uptake and histamine release induced by compound 48/80, substance P and egg-albumin (immunological release). In the absence of calcium all glycosides inhibited potassium uptake. Ouabain and digoxin enhanced the histamine release while digitoxigenin either had no effect or was slightly inhibitory. In the presence of calcium, the glycosides only affected potassium uptake and histamine release slightly. In the presence of lithium or lanthanum the enhancement of the histamine release was counteracted. Hydrophilic digitalis glycosides seem to enhance histamine release secondary to an increase in intracellular sodium. Lipophilic glycosides have no effect on the release.

Reversal by EGTA of the enhanced secretory responsiveness of mast cells due to treatment with ouabain.

The effect of EGTA on the enhancement by ouabain of compound 48/80-induced secretion from mast cells was compared with the effect on the Na(+)-K+ pump activity. The time-dependent secretory enhancement by ouabain was blocked by addition of EGTA to the cell suspension concomitantly with the addition of ouabain, and EGTA caused a large increase in the pump activity. Addition of 10 microM EGTA to ouabain-treated cells stopped but did not reverse the enhancement. The experiments show that the effect of ouabain was due to changes in a calcium pool utilized in compound 48/80-induced secretion following changes in the Na+,K+ pump activity.