Protein-polymer bioconjugation, immobilization, and encapsulation: a comparative review towards applicability, functionality, activity, and stability

Polymer-based biomaterials have received a lot of attention due to their biomedical, agricultural, and industrial potential. Soluble protein-polymer bioconjugates, immobilized proteins, and encapsulated proteins have been shown to tune enzymatic activity, improved pharmacokinetic ability, increased chemical and thermal stability, stimuli responsiveness, and introduced protein recovery. Controlled polymerization techniques, increased protein-polymer attachment techniques, improved polymer surface grafting techniques, controlled polymersome self-assembly, and sophisticated characterization methods have been utilized for the development of well-defined polymer-based biomaterials. In this review we aim to provide a brief account of the field, compare these methods for engineering biomaterials, provide future directions for the field, and highlight impacts of these forms of bioconjugation.

Comparison of Old and New Systemic Treatments for Moderate to Severe Atopic Dermatitis

PURPOSE OF REVIEW

Historically, systemic treatments for atopic dermatitis (AD) primarily consisted of immunosuppressive agents such as corticosteroids and Disease Modifying Antirheumatic Drugs (DMARDS), which provided symptomatic relief but often had long-term adverse effects. Newer treatments have shown significant efficacy with less side effects in clinical trials. This review discusses and compares conventional and newer systemic treatments for AD.

RECENT FINDINGS

Newer medications for AD including dupilumab, tralokinumab, lebrikizumab, and oral JAK inhibitors have been shown to be safe and efficacious. High dose cyclosporine and dupilumab were more effective than methotrexate and azathioprine in improving clinical signs of AD. High-dose upadacitinib was shown in another meta-analysis to be most effective in the measured outcomes but had the highest frequency of adverse events. Targeted biologic treatments are increasingly favored over traditional immunosuppressive treatments of AD. Treatment can be individualized based on potency, adverse side effects, mechanism of action, and administration preference. Ongoing research continues to expand treatment options for AD.

COVID-19 Vaccination in Patients with Inborn Errors of Immunity Reduces Hospitalization and Critical Care Needs Related to COVID-19: a USIDNET Report

BACKGROUND

The CDC and ACIP recommend COVID-19 vaccination for patients with inborn errors of immunity (IEI). Not much is known about vaccine safety in IEI, and whether vaccination attenuates infection severity in IEI.

OBJECTIVE

To estimate COVID-19 vaccination safety and examine effect on outcomes in patients with IEI.

METHODS

We built a secure registry database in conjunction with the US Immunodeficiency Network to examine vaccination frequency and indicators of safety and effectiveness in IEI patients. The registry opened on January 1, 2022, and closed on August 19, 2022.

RESULTS

Physicians entered data on 1245 patients from 24 countries. The most common diagnoses were antibody deficiencies (63.7%). At least one COVID-19 vaccine was administered to 806 patients (64.7%), and 216 patients received vaccination prior to the development of COVID-19. The most common vaccines administered were mRNA-based (84.0%). Seventeen patients were reported to seek outpatient clinic or emergency room care for a vaccine-related complication, and one patient was hospitalized for symptomatic anemia. Eight hundred twenty-three patients (66.1%) experienced COVID-19 infection. Of these, 156 patients required hospitalization (19.0%), 47 required ICU care (5.7%), and 28 died (3.4%). Rates of hospitalization (9.3% versus 24.4%, p < 0.001), ICU admission (2.8% versus 7.6%, p = 0.013), and death (2.3% versus 4.3%, p = 0.202) in patients who had COVID-19 were lower in patients who received vaccination prior to infection. In adjusted logistic regression analysis, not having at least one COVID-19 vaccine significantly increased the odds of hospitalization and ICU admission.

CONCLUSION

Vaccination for COVID-19 in the IEI population appears safe and attenuates COVID-19 severity.

Recent advances in immunomodulators for atopic dermatitis

PURPOSE OF REVIEW

Conventional treatments of atopic dermatitis have been inadequate, especially in patients with moderate-to-severe disease.

RECENT FINDINGS

In the past 5 years, four immunomodulators have been approved for the treatment of atopic dermatitis in children. These include dupilumab, ruxolitinib, upadacitinib, and abrocitinib. The review summarizes the pivotal phase 3 trials of these medications.

SUMMARY

The newer immunomodulators have transformed the treatment of atopic dermatitis, particularly in patients with moderate-to-severe disease. Dupilumab targets IL-4 and IL-13, which are the main causes of allergic inflammation, resulting in great efficacy and few side effects. Upadacitinib and abrocitinib are alternative systemic medications for adolescents who have failed or are unable to tolerate dupilumab. Ruxolitinib cream is the latest addition to the current topical therapy. It is indicated for children 12 years and older with mild-to-moderate atopic dermatitis. Further studies are needed to confirm its safety and efficacy for younger children and for patients with more severe disease.

Ensuring equitable access to guideline-based asthma care across the lifespan: Tips and future directions to the successful implementation of the new NAEPP 2020 guidelines, a Work Group Report of the AAAAI Asthma, Cough, Diagnosis, and Treatment Committee

The most recent recommendations from the 2020 National Asthma Education and Prevention Program Update and Global Initiative for Asthma 2021 guide evidence-based clinical decision making. However, given the present state of health disparities by age, income, and race, the equitable implementation and dissemination of these guidelines will be unlikely without further guidance. This work group report reviews the current state of the new asthma guideline implementation; presents updated evidence-based therapeutic options with attention to specific patient populations; and addresses barriers to the implementation of these guidelines in minoritized, historically marginalized, and underresourced communities. Allergists and immunologists can use practical ways to accomplish the goals of improved asthma care access and advanced asthma care across the life span, with specific considerations to historically marginalized populations. Modifiable barriers to guideline implementation include financial barriers, environmental factors, and allergy subspecialty access and care coordination. Various programs to improve access to guideline-based asthma care include community programs, school-based asthma programs, and digital health solutions, with an emphasis on reducing disparities by race.

Improving epinephrine autoinjector usability and carriage frequency among patients at risk of anaphylaxis: a quality improvement initiative

Although epinephrine autoinjectors (EAIs) are crucial for the management of anaphylaxis, patient carriage frequency of EAI is as low as 57% and usage of EAIs is erroneous 35%–43% of the time. Our objective was to improve patient carrying frequency of EAI and understanding of EAI usage.

We implemented a quality improvement initiative using consistent closed-loop education, redesigned clinic workflow, electronic medical record reminder-based interventions, and educational materials to improve patient EAI carriage compliance and understanding of EAI indications and proper technique.

The percentage of our patients who carried the EAI at all times increased from 55% to 93% in 6 months. Participants knowledge of EAI indications also improved from 22% to 91%. Patient demonstration scores of the EAI device improved from 21% to 91% as well.

Our quality improvement interventions demonstrated a significant improvement>80% in EAI carriage frequency, knowledge of indications, and proper device technique.

A case of delayed maculopapular eruption to ibuprofen and acute urticaria to acetaminophen

We present the unique case of a 33-year-old male referred to our clinic in search of analgesic options who was found to have a delayed hypersensitivity reaction to ibuprofen manifesting as a maculopapular rash and acute urticaria to acetaminophen. Non-steroidal anti-inflammatory drugs are associated with predictable reactions as well as immunoglobulin E-mediated reactions or T-cell mediated reactions. This case highlights the importance of knowledge of the different types of reactions to non-steroidal anti-inflammatory agents as well as the risk of cross reactivity. Delayed reaction to a single non-steroidal agent is rare; urticaria to acetaminophen is very rare. This is the first report we have found in the literature where one individual has a delayed reaction manifesting as rash to ibuprofen as well as urticaria to acetaminophen. We challenged our patient to aspirin which helped identify that his delayed reaction was only to ibuprofen and urticaria only to acetaminophen. The case also highlights the importance of an oral provocation challenge when no contraindications exist which helped us find that he could take celecoxib and avoid narcotics as initial therapy.

Peripheral Airway Impairment and Dysanapsis Define Risk of Uncontrolled Asthma in Obese Asthmatic Children

BACKGROUND

Factors that determine the relationship between obesity and poor outcomes in asthmatic children are not well understood. Dysanapsis and peripheral airway impairment (PAI) could provide an explanation in the obese asthmatic patient.

OBJECTIVES

To determine the effect of obesity on increased dysanapsis and PAI and establish the effect of obesity, dysanapsis, and PAI on increased risk of uncontrolled asthma.

METHODS

We evaluated 206 children with moderate to severe asthma, aged 4-18 years, to determine the relationship of body mass index (BMI) to increased dysanapsis and PAI, using reference values. We examined the probability of obesity, dysanapsis, and PAI increasing the risk of uncontrolled asthma by BMI categorically and BMI z scores using generalized linear model analyses.

RESULTS

Compared with normal-weight children, overweight and obese children had increased forced vital capacity % predicted and obesity increased odds of dysanapsis by 2.32 (P = .04), while PAI showed an age-dependent effect, with increased odds of 2.09 for children younger than 12 years (P = .08) and 54.14 for those 12 years and older (P = .003). For each unit increase in BMI z score, there was an increased odds ratio of 1.57 for dysanapsis (P = .009), greater in males, OR of 3.10, P = .009, and of 1.39 for PAI for those younger than 12 years (P = .042) and of 4.60 for those 12 years and older (P = .002). Obesity's relationship to uncontrolled asthma was indirect, as not significant when adjusted for the direct effect of dysanapsis and PAI, which were highly significant predictors, with increased odds of 28.01 for dysanapsis for those younger than 12 years (P < .001) and of 3.09 for PAI (P = .005).

CONCLUSIONS

Overweight and obesity significantly increase odds of dysanapsis and PAI, in an age and gender-specific manner, increasing the probability of uncontrolled asthma.

Effect of omalizumab on outcomes in patients with aspirin-exacerbated respiratory disease

Background: The current treatment for patients with aspirin-exacerbated respiratory disease (AERD) who have uncontrolled asthma or chronic rhinosinusitis is aspirin desensitization. For patients who are unable to undergo or do not benefit from aspirin desensitization, treatment with biologics is an option, although efficacy data for AERD is scarce. Objective: We reported a series of patients with AERD who were started on omalizumab and measured the outcomes to assess improvement. Methods: Adult patients with AERD who were initiated on omalizumab from January 2007 to January 2018 were included. We compared outcomes 6-12 months before initiating biologic therapy and during the last 6-12 months while they were on biologic therapy. Our study investigated the number of oral steroid courses, short-acting beta-agonists (SABA), antibiotics for sinusitis or pneumonia, emergency department visits, hospitalizations, pulmonary function tests, and changes in controller medications. Results: Twenty-nine patients were placed on omalizumab. Sixty-two percent demonstrated a reduction in the number of steroid courses (p = 0.0014) and number of SABA canisters used (p = 0.0005) during their last 12 months while on omalizumab. Eighty-six percent of the patients with AERD and on omalizumab demonstrated either a decrease in the number of steroid courses or number of SABA canisters used in the last year of the study. The patients with AERD and with concomitant immunoglobulin E (IgE) mediated respiratory disease showed a statistically significant reduction in the number of steroid courses and number of SABA canisters used while on omalizumab for 1 year (p = 0.002 and p = 0.005, respectively), whereas those without concomitant IgE-mediated respiratory disease did not have a substantial reduction in steroids or SABA canisters used. Conclusion: Our case series reported that omalizumab could effectively be used as an adjunct treatment for AERD, but additional larger and longitudinal studies are needed to corroborate these findings.

Development of a pediatric asthma predictive index for hospitalization

BACKGROUND

Variation in emergency department (ED) management for asthma exacerbation leads to disparities in care. Current asthma severity scores are insufficient to be used for hospitalization decisions.

OBJECTIVE

To develop and internally validate an asthma predictive index for hospitalization (APIH) to guide practitioners in their admission decision for children with asthma exacerbations.

METHODS

Data were collected from 12,066 children between 5 and 18 years old diagnosed with asthma exacerbation in the ED. Epidemiologic findings, number of inhaled corticosteroid canisters, short-acting β-blocker canisters, oral steroids, coexisting atopy, family history of atopy, insurance, and prior asthma ED visits or hospitalizations were compared between patients hospitalized and discharged. We used univariate analysis and multivariate analysis to determine the best predictor variables for hospitalization. Our study internally validated the prediction index to estimate future performance of the prediction rule.

RESULTS

The highest risk factors associated with asthma hospitalization from the ED are oxygen saturation less than 94%, respiratory rate greater than 31/min, history of pneumonia, and asthma ED visits in past 12 months. With a reduced predictive model that combined these risk factors, the odds ratio was 44.9 (95% CI, 32.8-61.4), which is extremely significant. Our C index of discrimination of 0.77 was similar to the validation C index of 0.78, which confirms a solid prediction model.

CONCLUSION

We have developed and internally validated a pediatric hospitalization prediction index for acute asthma exacerbation in the ED. Further studies are needed to externally validate the APIH before its implementation into clinical practice.

[A further case of tracheal paraganglioma]

Paragangliomas, or chemodectomas, are neuro-endocrine tumors of the neural type, derived from extra-adrenal paraganglia. Tracheal localizations are rare. We report the case of a patient with a paraganglioma of the upper part of the trachea. The tumor was totally removed by means of the resection of the subglottic trachea and anastomosis. Surgery is the treatment of such lesions, but can be difficult in cases of subglottic or juxta-carinal localizations.

[Two new cases of autonomous ectopic goiter]

We observed two cases of autonomous intrathoracic goiter in patients with no past history of thyroidectomy. After resection, the surgical specimens confirmed the non-malignant nature of the goiter. We discuss the literature on management of autonomous intrathoracic goiter.

Up-regulation of [3H]-des-Arg10-kallidin binding to the bradykinin B1 receptor by interleukin-1 beta in isolated smooth muscle cells: correlation with B1 agonist-induced PGI2 production

1. Binding of the specific bradykinin B1 receptor agonist, [3H]-des-Arg10-kallidin (-KD) was investigated in smooth muscle cells (SMC) isolated from rabbit mesenteric arteries (RMA). 2. [3H]-des-Arg10-KD specifically bound to interleukin-1 (IL-1)-treated RMA-SMC in a saturable fashion with an equilibrium dissociation constant (KD) of 0.3-0.5 nM. The number of binding sites per cell was 20,000-35,000. Kinins inhibited [3H]-des-Arg10-KD binding to RMA-SMC with an order of potency very similar to that observed in typical B1 specific bioassays: des-Arg9-bradykinin (BK) approximately KD >> BK. Furthermore, the B1 receptor antagonist [Leu8]des-Arg9-BK inhibited [3H]-des-Arg10-KD binding with an IC50 of 43 nM as expected for its effect at B1 receptors. The B2 receptor antagonists, NPC 567 and Hoe 140 only affected [3H]-des-Arg10-KD binding at very high concentrations (IC50 = 0.8 microM and IC50 > 10 microM, respectively). 3. Des-Arg9-BK (B1 agonist) and [Hyp3]Tyr(Me)8-BK (B2 agonist) did not induce prostacyclin (PGI2) production by RMA-SMC. Lipopolysaccharide (LPS) treatment of the cells did not affect the B1 agonist response whereas IL-1 beta treatment produced a 7 fold increase in des-Arg9-BK-stimulated PGI2 production. IL-1 beta also stimulated the response to B2 agonists. 4. Des-Arg9-BK-induced PGI2 secretion in IL-1-primed RMA-SMC was mediated by B1 receptors since it was inhibited by [Leu8]des-Arg9-BK (IC50 = 56-73 nM) but not by Hoe 140. High concentrations of NPC 567 (IC5o = 2.4 micro M) were required to inhibit PGI2 production induced by B1 agonists.5. IL- 1-treated RMA-SMC displayed a 5 fold increase in the number of B1 receptors without modification of the affinity constant, thus establishing a possible relationship between the receptor density and the IL-i-primed B1 response.6. LPS treatment of the cells induced a 4 fold increase in B1 receptor number without modifying PGI2 secretion. This observation suggests that IL-1 but not LPS, in addition to increase in the number of receptors, signals the cell to permit the coupling of B1 receptors to the PLA2/cyclo-oxygenase pathway.

Mediators involved in inflammation: effects of Daflon 500 mg on their release

Each step of an inflammatory reaction is triggered by one or several chemical or biological mediators such as arachidonic acid derivatives (prostaglandins [PG], leukotrienes [LT], or thromboxanes [TX]), vasoactive amines (histamine or serotonin), and oxygen free radicals (superoxide ion, O2-, or hydrogen peroxide, H2O2). In perivenous inflammation, these mediators play a prominent role in favoring vasodilatation (histamine), increasing membrane permeability (PGE2, histamine, free radicals) and providing a chemotactic signal for specialized cells, ie, neutrophil polynuclears, macrophages, lymphocytes (LTB4, free radicals). The antiinflammatory effects of Daflon 500 mg,* a micronized purified flavonoid fraction (90% diosmin, 10% hesperidin), were studied in different in vivo and in vitro models. In a model of inflammatory granuloma in the rat, Daflon 500 mg (100 mg/kg, orally) reduced edema formation and inhibited the synthesis for PGE2 (78.5%), PGF2 alpha (45.2%) and TXB2 (59.5%) (Damon et al, Arzneim-Forsch/Drug Res 37:1149-1153, 1987). Intravenous injection of Daflon 500 mg (25 and 50 mg/kg) reduced the hyperglycemia induced by injection of alloxan in rat. This effect of Daflon 500 mg was linked to its ability to scavenge active oxygen radicals, demonstrated in vitro using human neutrophils (Lonchampt et al, Arzneim-forsch/Drug Res 39:882-885, 1989) or mouse peritoneal macrophages (Bodinier et al, manuscript in preparation) stimulated by zymosan. The free radical scavenger effect of Daflon 500 mg is observed at concentrations ranging from 10(-7) M to 10(-4) M, with half-maximal effect between 10(-6) M and 10(-5) M. Thus, Daflon 500 mg behaves as a potent protective agent against inflammatory disorders. These properties may explain, at least in part, the clinical activity of Daflon 500 mg and justify its therapeutic use.

Effects of repeated treatments with an extract of Ginkgo biloba (EGb 761), bilobalide and ginkgolide B on the electrical activity of pancreatic beta cells of normal or alloxan-diabetic mice: an ex vivo study with intracellular microelectrodes

1. The effects of repeated (5-day) treatments with an extract of Ginkgo biloba leaves (EGb 761), bilobalide, and ginkgolide B on the in vitro electrical activity of insulin-secreting pancreatic beta cells of mice have been examined using intracellular microelectrodes. 2. EGb 761 (200 mg/kg/day, p.o.) protected beta cells against the toxic effects of alloxan (50 mg/kg, i.v.), an effect characterized by a restoration of membrane potential (Vr) and an increase in spike frequency (Fs/30), an indicator of insulin secretion. 3. Treatment of non-diabetic mice with EGb 761 (200 mg/kg/day, p.o.) increased Fs/30 of their beta cells, as tested by in vitro exposure of the cells to 11.1 mM glucose, an effect that also occurred with bilobalide (8 mg/kg/day, i.p.) but not with ginkgolide B (4 mg/kg/day, i.p.). 4. Since bilobalide and ginkgolide B caused opposite effects on the sensitivity of beta cells to glucose, the stimulatory effect of EGb 761 on Fs/30 may be attributed to its content of bilobalide. 5. In contrast to its ex vivo effect, the direct in vitro effect of EGb 761 (10 and 25 micrograms/ml) on beta cells favors a decrease in electrical activity, indicating that its in vivo action might be indirect (e.g. via the formation of an active metabolite).

Interleukin-1 impairs both vascular contraction and relaxation in rabbit isolated aorta

Incubation of rabbit aortic rings with interleukin-1 (100 U/ml) in vitro led to a depressed contractile response to norepinephrine, whether the endothelium was present or not. In both cases norepinephrine-induced contraction was restored in the presence of NG-methyl-L-arginine (300 microM), an inhibitor of nitric oxide synthesis. In interleukin-1-treated rings precontracted with norepinephrine (1 microM), the relaxing response to acetylcholine was totally suppressed independently on the presence of endothelium. High concentrations of acetylcholine (greater than 1 microM) induced a slight contraction which was of lower amplitude than that obtained in control endothelium-denuded rings and was increased in the presence of NG-methyl-L-arginine. These results show that interleukin-1 (i) affects not only vascular contraction but also relaxation and (ii) involves both endothelial and non-endothelial factors. These observations suggest an impairment of the whole vascular reactivity during septic shock.

[Von Economo-Cruchet lethargic encephalitis and its relation to HIV infection]

The AIDS epidemic is currently considered to be the first retroviral disease in humans. However, in the large volume of work on von Economo-Cruchet's encephalitis lethargica, the authors reveal a series of common points between both diseases. The progress of both diseases is identical at every stage, with neurotropism, premature psychological disorders, mononucleasic syndrome, similar somatic manifestations of the viral attack and terminal dementia. The anatomo-pathological and epidemiological data, along with the hypothesis that encephalitis lethargica is sexually transmitted, reinforce the idea of a relationship between the two diseases. The interest which would be aroused by the discovery of a viral origin of encephalitis lethargica and the resulting experimental elements seem to make it worthwhile leaving the question open in order to find a precise answer. We are calling on all our colleagues in basic research to seek a solution to what we think is an essential question.

Evidence for a GTP-dependent increase in membrane permeability for calcium in NG108-15 microsomes

The effect of GTP on Ca2+ uptake and release was studied in a microsomal fraction isolated from neuroblastoma x glioma hybrid NG108-15 cells. GTP did not alter the ATP-dependent initial uptake of Ca2+ but markedly enhanced the efflux of Ca2+ from microsomes. GTP-dependent Ca2+ release requires the presence of millimolar concentration of Mg2+. The effect of GTP was not mimicked by other nucleotides and was competitively blocked by the thiophosphate analogue of GTP, GTP gamma S but not by the non-hydrolyzable nucleotide GMP-PNP. Addition of an inhibiting concentration of GTP gamma S after completion of GTP-induced calcium release did not result in a re-uptake of Ca2+, showing the irreversibility of the releasing effect of GTP. Our data are consistent with the hypothesis of Ca2+-dependent GTP-induced opening of a channel responsible for vectorial transport of Ca2+ ions from one intracellular compartment to another. A model is proposed suggesting that the GTP-binding protein is a GTP-specific diacylglycerol kinase.

The Na+/K+/Cl- cotransport in C6 glioma cells. Properties and role in volume regulation

The role of the Na+/K+/Cl- cotransporter in the regulation of the volume of C6 astrocytoma cells was analyzed using isotopic fluxes and cell cytometry measurements of the cell volume. The system was inhibited by 'loop diuretics' with the following order of potency: benzmetanide greater than bumetanide greater than piretanide greater than furosemide. Under physiological conditions of osmolarity of the incubation media, equal rates of bumetanide-sensitive inward and outward K+ fluxes were observed. Blockade of the Na+/K+/Cl- cotransporter with bumetanide did not lead to a modification in the mean cell volume. When C6 cells were incubated in an hyperosmotic solution, a cell shrinkage was observed. It was accompanied by a twofold increase in the activity of the Na+/K+/Cl- cotransport, which then catalyzed the net influx of K+. In spite of this increased activity, no cell swelling could be measured. Incubation of the cells in an iso-osmotic medium deprived of either Na+, K+ or Cl- also produced cell shrinkage. Large activations (up to tenfold) of the Na+/K+/Cl- cotransport together with a cell swelling back to the normal volume were observed upon returning ion-deprived C6 cells to a physiological solution. This cell swelling was completely prevented in the presence of bumetanide. It is concluded that the Na+/K+/Cl- cotransport system is one of the transport systems involved in volume regulation of glial cells. The system can either be physiologically quiescent or active depending on the conditions used. A distinct volume regulating mechanism is the Na+/H+ exchange system.

Calcium modulation of inositol 1,4,5-trisphosphate-induced calcium release from neuroblastoma x glioma hybrid (NG108-15) microsomes

Subcellular fractions of neuroblastoma x glioma (NG108-15) hybrid cells were used to study the mechanism of inositol 1,4,5-trisphosphate-induced calcium release. A microsomal fraction, enriched in endoplasmic reticulum and plasma membranes and almost devoid of mitochondria, was the most active in inositol trisphosphate- or GTP-dependent release of calcium. Neither GTP nor inositol 1,4,5-trisphosphate affected the calcium efflux mediated by the other reagent, suggesting that inositol trisphosphate and GTP act on different calcium-sequestrating vesicles. The stimulation of calcium release by GTP was relatively slow (t1/2 = 90 s), dependent on polyethyleneglycol, and greater at 2 X 10(-5) M calcium (5 nmol X min-1 X mg-1) than at 10(-6) M calcium (0.8 nmol X min-1 X mg-1). The inositol trisphosphate-induced calcium efflux was not mimicked by inositol monophosphate; it was fast (t1/2 less than 10 s) and unaffected by 3% polyethyleneglycol. The amount of calcium released by inositol trisphosphate was greatest at 10(-6) M external calcium (1 nmol X min-1 X mg-1) and it was undetectable at 2 X 10(-5) M calcium. A feedback inhibition of the inositol trisphosphate-induced calcium release by cytoplasmic calcium provides a safety mechanism preventing deleterious effects of abnormally high calcium levels.

The Na+/H+ antiport of eukaryotic cells: relationship between the kinetic properties of the system and its physiological function

The Na+/H+ antiport is present in the plasma membrane of virtually all vertebrate cells and it plays a central role in cell homeostasis. The pharmacological properties and the characteristics of the interaction of extracellular Na+, Li+, H+ and of intracellular H+ with the Na+/H+ antiport are reviewed herein. The kinetic properties of the system are shown to be essential for defining its four main physiological functions: transepithelial ion transport, control of the pHi, control of the intracellular Na+ concentration, and control of the cell volume. The activity of the Na+/H+ antiport can be modulated by a large number of effectors which are thought to act via protein kinases. At least three mechanisms of activation of the Na+/H+ exchanger are defined from the analysis of the kinetic properties of the system. Activation of the Na+/H+ antiport leads to very different consequences, depending upon the activity of other ion transporting systems in the membrane.

The Na+/H+ exchange system in glial cell lines. Properties and activation by an hyperosmotic shock

The properties of the Na+/H+ exchange system in the glial cell lines C6 and NN were studied from 22Na+ uptake experiments and measurements of the internal pH (pHi) using intracellularly trapped biscarboxyethyl-carboxyfluorescein. In both cell types, the Na+/H+ exchanger is the major mechanism by which cells recover their pHi after an intracellular acidification. The exchanger is inhibited by amiloride and its derivatives. The pharmacological profile (ethylisopropylamiloride greater than amiloride greater than benzamil) is identical for the two cell lines. Both Na+ and Li+ can be exchanged for H+. Increasing the external pH increases the activity of the exchanger in the two cell lines. In NN cells the external pH dependence of the exchanger is independent of the pHi. In contrast, in C6 cells, changing the pHi value from 7.0 to 6.5 produces a pH shift of 0.6 pH units in the external pH dependence of the exchanger in the acidic range. Decreasing pHi activates the Na+/H+ exchanger in both cell lines. Increasing the osmolarity of the external medium with mannitol produces an activation of the exchanger in C6 cells, which leads to a cell alkalinization. Mannitol action on 22Na+ uptake and the pHi were not observed in the presence of amiloride derivatives. Mannitol produces a modification of the properties of interaction of the antiport with both internal and external H+. It shifts the pHi dependence of the system to the alkaline range and the external pH (pHo) dependence to the acidic range. It also suppresses the interdependence of pHi and pHo controls of the exchanger's activity. NN cells that possess an Na+/H+ exchange system with different properties do not respond to mannitol by an increased activity of the Na+/H+ exchanger. The action of mannitol on C6 cells is unlikely to be mediated by an activation of protein kinase C.

[3H]Ethylpropylamiloride, a ligand to analyze the properties of the Na+/H+ exchange system in the membranes of normal and hypertrophied kidneys

[3H]Ethylpropylamiloride is a useful radioactive label to identify the Na+/H+ exchange system (Vigne, P., Frelin, C., Audinot, M., Borsotto, M., Cragoe, E. J., and Lazdunski, M. (1984) EMBO J. 3, 2647-2651). This paper extends the analysis of the properties of interaction of [3H]ethylpropylamiloride with the exchanger and describes its use with hypertrophied kidneys. [3H]Ethylpropylamiloride-binding sites copurify with the luminal membrane marker alkaline phosphatase but not with the basolateral membrane marker (Na+,K+)ATPase, thus indicating an asymmetric distribution of the Na+/H+ exchanger. Specific [3H]ethylpropylamiloride binding is dependent on pH. The pH dependency indicates that an ionizable function with a pKapp of 7.0 is essential in the association of the amiloride derivative. H+ acts competitively on [3H]ethylpropylamiloride binding; Na+, Li+, or cholinium ions have no effect on the association. Compensatory adaptation of the kidney to chronic reduction of renal mass is accompanied by a 1.7-fold increase in the activity of the Na+/H+ exchange system. Properties of interaction of internal and external pH with the Na+/H+ exchanger of normal and hypertrophied kidneys are identical. Titration of [3H]ethylpropylamiloride-binding sites in normal and hypertrophied kidneys suggests that the increased activity of the Na+/H+ exchange system is not accompanied by an increased concentration of exchangers.

Taurine transport in brush border membrane vesicles isolated from hyper- and normotaurinuric mouse kidney

The mouse strain C57BL is characterized by a high urinary fractional excretion of taurine. Hypertaurinuric [tau(-)] C57BL mice and three normal taurine 'excretors' [tau(+)]-Swiss, A/J, and C3H-were compared. Clearance experiments showed that fractional excretion of taurine was 4-8 times higher in C57BL relative to the other strains. Transport studies performed in brush border membrane vesicles, isolated from C57BL and C3H mouse renal cortex, showed that D-glucose uptake was similar in both strains while the taurine uptake appeared to be faster in tau(+) than in tau(-) mice. This difference was observed only in the presence of an inwardly directed NaCl gradient. The comparison of kinetic parameters showed a significant difference of apparent Km values: 90.8 +/- 11.4 microM in tau(+) mice vs. 129.5 +/- 17.1 microM in tau(-) mice. Jmax were not significantly different in both strains. These observations suggest a lower affinity of the taurine brush border membrane carrier in the hypertaurinuric strain as compared to the normotaurinuric mice. It is concluded that, in addition to a possible alteration of peritubular taurine efflux described by Rozen et al. (1983), a defect of taurine transport at the luminal membrane cannot be excluded and could account for the hypertaurinuria of the C57BL mice.

A sodium-independent mechanism for L-arginine uptake by rat renal brush border membrane vesicles

L-arginine accumulation in renal cortex slices or in brush border membrane vesicles differs from that of neutral amino acids and sugars, since it can occur despite a lack of sodium in the incubation medium. L-arginine uptake was measured under different conditions in order to determine the relative importance of the Na+-independent component of this transport. In contrast to D-glucose, which was accumulated into the vesicles only in the presence of a NaCl gradient, the accumulation of L-arginine was induced by NaCl, LiCl, KCl, or choline Cl gradients. The uptakes of L-arginine and D-glucose wer proportional to the membrane potential (inside less than 0), but the presence of Na+ was not required for the L-arginine uptake. No difference was observed in Kj values of the L-arginine uptake measured with low or high concentration of salt (Li+ or Na+). Jmax were also in the same range of magnitude. An influx of D-glucose or L-alanine (Na+-cotransported molecules) induced an increase of the sodium content in vesicles equilibrated with 22Na; the L-arginine uptake did not induce it. These different results suggest that the electrical potential and not the chemical gradient was the major driving force for the L-arginine uptake.