ARCTIC: durvalumab with or without tremelimumab as third-line or later treatment of metastatic non-small-cell lung cancer.

BACKGROUND: Many patients with metastatic non-small-cell lung cancer (mNSCLC) experience disease progression after first- and second-line treatment; more treatment options are required for these patients. ARCTIC, a phase III, randomized, open-label study, assessed durvalumab ± tremelimumab versus standard of care (SoC) as ≥ third-line treatment of mNSCLC. PATIENTS AND METHODS: ARCTIC comprised two independent sub-studies. Study A: 126 patients with ≥25% of tumor cells (TCs) expressing programmed cell death ligand-1 (PD-L1) were randomized (1 : 1) to durvalumab [up to 12 months 10 mg/kg every 2 weeks (q2w)] or SoC. Study B: 469 patients with PD-L1 TC <25% were randomized (3 : 2 : 2 : 1) to durvalumab + tremelimumab (12 weeks durvalumab 20 mg/kg + tremelimumab 1 mg/kg q4w then 34 weeks durvalumab 10 mg/kg q2w), SoC, durvalumab (up to 12 months 10 mg/kg q2w), or tremelimumab (24 weeks 10 mg/kg q4w then 24 weeks q12w). Primary end points: overall survival (OS) and progression-free survival (PFS) for durvalumab versus SoC (study A; descriptive only) and durvalumab + tremelimumab versus SoC (study B). RESULTS: Study A: median OS 11.7 (durvalumab) versus 6.8 (SoC) months {hazard ratio (HR) 0.63 [95% confidence interval (CI), 0.42-0.93]}; median PFS 3.8 (durvalumab) versus 2.2 (SoC) months [HR 0.71 (95% CI, 0.49-1.04)]. Study B: median OS 11.5 (durvalumab + tremelimumab) versus 8.7 (SoC) months [HR 0.80 (95% CI, 0.61-1.05); P = 0.109]. Median PFS of 3.5 months for both groups [HR 0.77 (95% CI, 0.59-1.01); P = 0.056]. Treatment-related grade 3/4 adverse events: 9.7% (durvalumab) and 44.4% (SoC; study A) and 22.0% (durvalumab + tremelimumab) and 36.4% (SoC; study B). CONCLUSIONS: In heavily pretreated patients with mNSCLC, durvalumab demonstrated clinically meaningful improvements in OS and PFS versus SoC (patients with PD-L1 TC ≥25%); numerical improvements in OS and PFS for durvalumab + tremelimumab versus SoC were observed (patients with PD-L1 TC <25%). Safety profiles were consistent with previous studies. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT02352948.

Glutaraldehyde fixation of the cAMP-dependent Na+/H+ exchanger in trout red cells.

It has been shown that the addition of a beta-adrenergic catecholamine to a trout red blood cell suspension induces a 60-100-fold increase of sodium permeability resulting from the activation of a cAMP-dependent Na+/H+ antiport. Subsequent addition of propranolol almost instantaneously reduces the intracellular cAMP concentration, and thus the Na permeability, to their basal values (Mahé et al., 1985). If glutaraldehyde (0.06-0.1%) is added when the Na+/H+ exchanger is activated after hormonal stimulation, addition of propranolol no longer inhibits Na permeability: once activated and fixed by glutaraldehyde, the cAMP dependence disappears. Glutaraldehyde alone causes a rapid decrease in the cellular cAMP concentration. In its fixed state the antiporter is fully amiloride sensitive. The switching on of the Na+/H+ exchange by cAMP is rapidly (2 min) followed by acute but progressive desensitization of the exchanger (Garcia-Romeu et al., 1988). The desensitization depends on the concentration of external sodium, being maximal at a normal Na concentration (145 mM) and nonexistent at a low Na concentration (20 mM). If glutaraldehyde is added after activation in nondesensitizing conditions (20 mM Na), transfer to a Na-rich medium induces only a very slight desensitization: thus the fixative can "freeze" the exchanger in the nondesensitizing conformation. NO3- inhibits the activity of the cAMP-dependent Na+/H+ antiporter of the trout red blood cell (Borgese et al., 1986). If glutaraldehyde is added when the cells are activated by cAMP in a chloride-containing medium, the activity of the exchanger is no longer inhibited when Cl- is replaced by NO3-. Conversely, after fixation in NO3- medium replacement of NO3- by Cl- has very little stimulatory effect. This indicates that the anion dependence is not a specific requirement for the exchange process but that the anion environment is critical for the switching on of the Na+/H+ exchanger and for the maintenance of its activated configuration.

Therapy with imatinib mesylate (Glivec) preceding allogeneic stem cell transplantation (SCT) in relapsed or refractory Philadelphia-positive acute lymphoblastic leukemia (Ph+ALL).

Imatinib has pronounced antileukemic activity in Ph+ALL, although responses are usually short. To determine whether imatinib may facilitate allogeneic SCT in relapsed or refractory Ph+ALL, we evaluated 46 consecutive, not previously transplanted patients who were enrolled in phase II studies of imatinib. Of 30 patients eligible for SCT, 22 (73%) were actually transplanted. Ten patients were in complete hematologic remission (CHR) (n = 5) or had a complete marrow response (CMR) (n = 5) at the time of SCT, 12 patients had again relapsed or were refractory. After SCT, 18 patients were in complete remission, one patient was refractory, three patients died prior to response assessment. Seven patients (32%) are in ongoing complete remission with a median follow-up of 9.4 (range 1.7-23.8) months. Seven patients (32%) relapsed a median of 5.2 months after SCT. Transplant-related mortality (TRM) was 36%. Probability of disease-free survival (DFS) is 25.5 +/- 9.8% overall and 51.4 +/- 17.7% when SCT was performed in CHR or CMR, compared with 8.3 +/- 8% for SCT during overt leukemia (P = 0.06). In conclusion, imatinib is a well-tolerated salvage therapy prior to allogeneic SCT in patients with Ph+ALL, but requires that SCT be performed within a few weeks of starting treatment to avoid resistance. Disease status at time of transplantation is an important determinant of DFS and TRM.

Serial minimal residual disease (MRD) analysis as a predictor of response duration in Philadelphia-positive acute lymphoblastic leukemia (Ph+ALL) during imatinib treatment.

Patients with refractory or relapsed Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) rarely have prolonged responses to salvage therapy, including imatinib, resulting in a short opportunity for potentially curative stem cell transplantation. To identify minimal residual disease (MRD) parameters predictive of imminent relapse, we quantitated Bcr-Abl expression by real-time PCR in peripheral blood (PB) and bone marrow (BM) of 24 Ph+ALL patients after achieving a complete response and MRD minimum. The ratio of Bcr-Abl and glyceraldehyde-3-phosphate dehydrogenase copies, magnitude of increase and velocity of increase were evaluated regarding subsequent time intervals to relapse, death or censoring. High Bcr-Abl levels >/=5 x 10(-4) in PB (n=23) and >/=10(-4) in BM (n=18) were significantly associated with short time periods to relapse. Bcr-Abl increases >2 logarithmic units (log) in PB, but not in BM preceded short-term relapse. The velocity of Bcr-Abl increases predicted response duration in PB (cutoff: 1.25 log/30 days) and BM (0.6). Bcr-Abl level and velocity of increase in BM as well as magnitude of increase in PB correlated with remaining periods of survival and predicted relapse within 2 months in nine of 10, 10 of 11 and four of four patients, respectively. Thus, these MRD parameters may guide timing and intensity of therapeutic modifications.

Efficacy and safety of imatinib mesylate (Glivec) in combination with interferon-alpha (IFN-alpha) in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL).

Imatinib has marked antileukemic activity in advanced Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL), but secondary resistance develops rapidly, reflecting the limitations of single-agent therapy. Experimental data suggest that interferon-alpha (IFN-alpha) enhances the antileukemic activity of imatinib. We therefore examined combined imatinib and low-dose IFN-alpha in six patients with Ph+ALL who were ineligible for stem cell transplantation. All patients had received imatinib for 0.5-4.8 months prior to IFN-alpha, for relapsed (n=3) or refractory (n=1) Ph+ALL or as an alternative to chemotherapy following severe treatment-related toxicity (n=2). Five patients were in hematologic remission (CR) with minimal residual disease (MRD+), one patient was refractory to imatinib. Four of the five MRD+ patients are alive in CR after a median treatment duration of 20 (11-21) months. Two of these patients are in continuous CR 21 months after imatinib was initiated, while the other two patients experienced an isolated meningeal relapse that was successfully treated with additional intrathecal chemotherapy. Sustained molecular remissions were achieved in three patients and are ongoing 13 and 10.5 months after central nervous system (CNS) relapse and 6 months after starting concurrent IFN-alpha and imatinib, respectively. Marrow relapse occurred in one of the five MRD+ patients. Combination treatment was associated with a complete marrow response of 5 months duration in the imatinib-refractory patient. Imatinib combined with low-dose IFN-alpha may achieve prolonged hematologic and molecular remissions in a subset of patients with advanced Ph+ALL, who are not candidates for allogeneic SCT. CNS prophylaxis is necessary and may enhance the antileukemic activity of imatinib and IFN-alpha.

Early modification of host cell gene expression induced by HIV-1.

OBJECTIVE: Characterization of the effects of infection with HIV-1 on cellular gene expression. DESIGN AND METHODS: Differential RNA display was applied to compare uninfected and HIV-1LAI-infected CEM cells 24 h post-inoculation. Differential bands were selected, cloned and several clones per band were sequenced. RNase protection assay was used to confirm differential display findings in HIV-1LAI-infected CEM cells as well as in another T-cell line (H9) infected with a different strain (HIV-1 SF33) RESULTS: Twelve differentially expressed bands, six up- and six downregulated in HIV-infected cells compared with controls, were selected. Four of the six upregulated bands were HIV transcripts. RNase protection assay of the remaining eight bands confirmed differential expression of four genes, including induction of a mariner transposase and moesin as well as suppression of alpha-nascent polypeptide-associated complex and mitochondrial heat shock protein 75 in HIV-1-infected cell cultures. Furthermore, a significant increase of glioma pathogenesis-related protein was found by RNase protection assay. CONCLUSIONS: Based on this initial limited differential display analysis, it was estimated that expression of 3% of the host genes was altered by HIV-1. Amongst the identified gene modifications, the induction of a mariner transposase may alter cellular gene expression itself, whilst the enhanced expression of glioma pathogenesis-related protein suggests a role in the host cell response to viral infection. The increase in moesin may facilitate viral budding and uptake. Furthermore, the suppression of alpha-nascent polypeptide-associated complex may promote translocation of HIV-1 polypeptides into the endoplasmic reticulum, whereas the downregulation of mitochondrial heat shock protein 75 may contribute to a cytopathic effect on mitochondria and possibly impairs antigen presentation.

Differential expression profiles of apoptosis-affecting genes in HIV-infected cell lines and patient T cells.

OBJECTIVE: To clarify the molecular mechanisms of HIV-induced apoptosis. DESIGN: The assessment of expression patterns for genes affecting the interrelated cell cycle and apoptosis processes in HIV-1LAI-infected T lymph oblastoid (CEM) cells, as well as CD4 and CD8 cells from HIV-infected individuals and controls. METHODS: The kinetics of HIV infection in CEM cells were defined by flow cytometry of green fluorescent protein expression from a reporter vector. Apoptosis of CEM cells was measured by propidium iodine staining and flow cytometry. Gene expression levels were determined by a multiprobe RNase protection assay. RESULTS: The infection and apoptosis of CEM cells were associated with enhanced expression of Bax, Bcl-2, Bcl-X(L) and caspase 1 (ICE). There was increased expression of Bcl-2 and caspase 1 and decreased expression of cyclin-dependent kinase inhibitor p21CIP1 in CD4 cells of HIV-infected individuals compared with uninfected controls. The CD8 cells of HIV-infected individuals exhibited increased expression of Bcl-2, Bcl-X(L), Bax and caspase 1 but, in contrast to the CD4 subset, they showed elevated expression of p21CIP1 and p16INK4a compared with controls. CONCLUSIONS: The Bax increase in CEM cells appears to be a direct effect associated with a high frequency of infection and apoptosis, because it was not found in the CD4 cells of patients. In contrast, the increase of Bax in the CD8 cells of patients seems to be an indirect effect. Increases in Bcl-2, Bcl-X(L) and caspase 1 in HIV-infected CEM cells may be caused by both direct and indirect mechanisms, because they also occurred in CD4 and CD8 cells of HIV-infected individuals. In addition, the low expression of p21CIP1 in the CD4 subset of HIV-infected individuals could promote apoptosis, whereas the high expression of p21CIP1 and p16INK4a in the CD8 subset may lead to a state of anergy, akin to replicative senescence.

Does sphingomyelin inhibit the erythrocyte anion transport system?

The anion transport protein of the human erythrocyte membrane, band 3, was incorporated into unilamellar sphingomyelin vesicles. The vesicles showed a rapid sulfate efflux which could be inhibited by specific inhibitors of the erythrocyte anion transport system. All band 3 molecules contributing to the inhibitor-sensitive flux component were arranged 'right-side-out'. The turnover number of the transport protein for sulfate transport was virtually identical to that in phosphatidylcholine bilayers and around 6 times larger than in human erythrocyte membranes. Thus, in contrast to other claims, sphingomyelin does not inhibit the erythrocyte anion transport system.

The turnover number for band 3-mediated sulfate transport in phosphatidylcholine bilayers.

The anion transport system of the human erythrocyte membrane was reconstituted in unilamellar phosphatidylcholine vesicles, and a vesicle subpopulation of a narrow size distribution was isolated from the sample by gel filtration. In this subpopulation, the turnover number of the transport protein (the band 3 protein) for sulfate transport was determined. It was found that, in the reconstituted system, the protein transports sulfate 5-10 times faster than in the human erythrocyte membrane.

Arrestin from nucleated red blood cells binds to bovine rhodopsin in a light-dependent manner.

Using a panel of monoclonal antibodies, it has previously been demonstrated that the cytosol of nucleated red cells (trout and turkey) contains a protein similar to arrestin, a soluble protein found so far only in the photosensitive cells and which, by binding to photoexcited rhodopsin, inhibits the phototransduction process. The role of this arrestin-like protein in non-photosensitive cells is questionable. In this report we present evidence that partially purified red blood cell arrestin (RBC arrestin) behaves functionally like bovine retinal arrestin: it binds to phosphorylated bovine rhodopsin only when this receptor has been photoactivated. Thus RBC arrestin and bovine retinal arrestin are closely related both structurally and functionally. By analogy with the function of retinal arrestin, it is proposed that RBC arrestin is involved in desensitization of membrane transport proteins and/or adrenergic receptors.

Immunological detection of arrestin, a phototransduction regulatory protein, in the cytosol of nucleated erythrocytes.

Cytosolic extracts of trout and turkey erythrocytes were tested for their immunoreactivity with polyclonal and monoclonal antibodies to retinal arrestin (S-antigen), a cytosolic protein of photoreceptor cells involved in the desensitization of rhodopsin. After adsorption or immunoaffinity chromatography of the extracts, these antibodies specifically recognized a protein having a molecular weight similar to that of retinal arrestin. Because the G-protein-mediated transduction systems, such as visual and beta-adrenergic systems, display a high degree of structural and functional homology, the presence of arrestin-like proteins in non-photosensitive cells suggests that these proteins are involved in the transduction of chemical signals, with a possible role in receptor desensitization.

Hematologic and cytogenetic remission by STI571 (Glivec) in a patient relapsing with accelerated phase CML after second allogeneic stem cell transplantation.

We describe the clinical activity of the ABL kinase inhibitor STI571 in a patient with accelerated phase of chronic myeloid leukemia (CML) relapsing after a second allogeneic BMT and with minimal levels of donor chimerism. STI571 resulted in rapid elimination of leukemic cells with ensuing prolonged severe leukopenia and neutropenia complicated by neutropenic fever and colitis. Subsequent hematopoietic recovery was driven by donor derived cells and was associated with grade 3 graft-versus-host disease (GVHD). STI571 induced sustained hematological and cytogenetic remission combined with controllable GvHD, therapeutic goals not achieved by two preceding allogeneic transplants and repeated donor lymphocyte transfusions (DLT).

Stable molecular remission induced by imatinib mesylate (STI571) in a patient with CML lymphoid blast crisis relapsing after allogeneic stem cell transplantation.

We report the response to the ABL kinase inhibitor imatinib mesylate (STI571) in a patient with chronic myeloid leukemia (CML) who relapsed twice after dose-reduced allogeneic stem cell transplantation (alloSCT) for B lymphoid blast crisis (BC) and failed to develop an antileukemic response despite grade 3 graft-versus-host disease (GvHD). Complete hematologic, cytogenetic and molecular responses were achieved within 9 weeks of therapy and are maintained after 27 months. Extensive chronic skin GvHD necessitating immunosuppressive therapy developed after 14 months. This case illustrates the ability of imatinib to induce sustained hematologic and molecular remissions in some patients relapsing with advanced stage CML after alloSCT.

Analysis of pancreatic serum markers in patients with cystic fibrosis.

The occurrence of increased serum concentrations of pancreatic tumor markers CA 19-9, CA 50 and elastase 1 in cystic fibrosis (CF) prompted us to investigate the pancreatic markers DU-PAN-2 and TATI. DU-PAN-2 was measured in serum samples of 48 CF patients, 42 pediatric control patients, and 51 parents of CF children by a competition radioimmunoassay (RIA). A commercially available RIA test kit was used to measure TATI serum levels of 38 CF patients and 40 control patients. Nineteen percent of CF patients, 0% of the control group, and 6% of the parents exceeded the DU-PAN-2 threshold value of 300 U/ml. TATI concentrations were increased (greater than 20 micrograms/L) in 24% of CF patients and in 17% of control patients. The sensitivity-specificity curve of DU-PAN-2 was similar to those of CA 50 and elastase 1 but less discriminating than that of CA 19-9. However, the sensitivity-specificity profile of CA 19-9 can only be marginally enhanced in a range of low specificity by simultaneously determining elastase 1 and/or DU-PAN-2 antigens. TATI does not provide any diagnostic use in CF.

Asymmetric reconstitution of the erythrocyte anion transport system in vesicles of different curvature: implications for the shape of the band 3 protein.

The anion transport protein of the human erythrocyte membrane, band 3, was solubilized and purified in solutions of the non-ionic detergent nonaethylene glycol lauryl ether and then reconstituted in spherical egg phosphatidylcholine bilayers as described earlier (U. Scheuring, K. Kollewe, W. Haase, and D. Schubert, J. Membrane Biol. 90, 123-135 (1986)). The resulting paucilamellar proteoliposomes of average diameter 70 nm were transformed into smaller vesicles by French press treatment and fractionated according to size by gel filtration. The smallest protein-containing liposomes obtained had diameters around 32 nm; still smaller vesicles were free of protein. All proteoliposome samples studied showed a rapid sulfate efflux which was sensitive to specific inhibitors of band 3-mediated anion exchange. In addition, the orientation of the transport protein in the vesicle membranes was found to be "right-side-out" in all samples. This suggests that the orientation of the protein in the vesicle membranes is dictated by the shape of the protein's intramembrane domain and that this domain has the form of a truncated cone or pyramid.

A mixing chamber to enucleate avian and fish erythrocytes: preparation of their plasma membrane.

Biochemical studies of the plasma membrane and the cytoskeleton of nucleated erythrocytes are strongly limited by the difficulties encountered in enucleating large quantities of cells. We describe an easily built hydrodynamic system which allows rapid preparation of large amounts of avian and fish erythrocyte plasma membranes. The contents of two 25-ml syringes containing hemolyzed nucleated erythrocytes are forced through four capillaries to a specially designed mixing chamber which fills a collecting syringe. The 50-ml erythrocyte suspension can be processed in 2 s. The high speed flow is achieved with a hand-activated piston. The turbulences in the mixing chamber are carried to an optimal efficiency by the vis-à-vis disposition of the four mixing jets. The enucleated membranes are separated from the nuclei and residual nucleated cells by differential centrifugations. They do not show contamination with nuclear material. Erythrocytes from chicken and trout have been used. They present striking differences in their stability toward hydrodynamic disruption, erythrocytes from chicken being far more stable. Ninety-five percent of trout erythrocytes are enucleated after only one run through the mixing chamber. Two runs performed at the maximal flow rate are necessary to enucleate chicken erythrocytes with a yield of 80%. In the former case most of the purified enucleated plasma membranes are fragmented in small vesicles while they retain a large size in the case of chicken erythrocytes. The proteins of the membranes thus prepared are characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis: we found that erythrocyte membranes from trout are remarkable for their small spectrin content compared to those from chicken.

A new method for the reconstitution of the anion transport system of the human erythrocyte membrane.

The anion transport protein of the human erythrocyte membrane, band 3, was solubilized and purified in solutions of the non-ionic detergent Triton X-100. It was incorporated into spherical lipid bilayers by the following procedure: Dry phosphatidylcholine was suspended in the protein solution. Octylglucopyranoside was added until the milky suspension became clear. The sample was dialyzed overnight against detergent-free buffer. Residual Triton X-100 was removed from the opalescent vesicle suspension by sucrose density gradient centrifugation and subsequent dialysis. Sulfate efflux from the vesicles was studied, under exchange conditions, using a filtration method. Three vesicle subpopulations could be distinguished by analyzing the time course of the efflux. One was nearly impermeable to sulfate, and efflux from another was due to leaks. The largest subpopulation, however, showed transport characteristics very similar to those of the anion transport system of the intact erythrocyte membrane: transport numbers (at 30 degrees C) close to 20 sulfate molecules per band 3 and min, an activation energy of approx. 140 kJ/mol, a pH maximum at pH 6.2, saturation of the sulfate flux at sulfate concentrations around 100 mM, inhibition of the flux by H2DIDS and flufenamate (approx. KI-values at 30 degrees C: 0.1 and 0.7 microM, respectively), and "right-side-out" orientation of the transport protein (as judged from the inhibition of sulfate efflux by up to 98% by externally added H2DIDS). Thus, the system represents, for the first time, a reconstitution of all the major properties of the sulfate transport across the erythrocyte membrane.

CA 19-9, CA 50 and elastase 1 as additional markers of cystic fibrosis.

Since reliable diagnosis of cystic fibrosis (CF) is still difficult, the occurrence of serum markers CA 19-9, CA 50 and elastase 1 was analysed. Serum levels of CA 19-9, CA 50, CA 125 and elastase 1 were estimated in 54 CF patients as well as in a control group of 66 children of similar age suffering from various other diseases and in 57 parents of CF patients. In 67% of CF patients CA 19-9 was higher than 37 U/ml, whereas 8% of the control group and only 2% of the parents showed an increased concentration. In the case of CA 50, 65% of the CF group, 21% of the control and none of the parents exhibited concentrations higher than 17 U/ml. In CF 22% showed decreased, 8% increased elastase 1 values. In the control group 2% had less than 80 ng/dl and 3% had higher elastase 1 levels than 400 ng/dl. In parents there were only increased levels in 4%. Accordingly CA 19-9 has been proven as a suitable marker and its sensitivity can be improved from 67% to 86% by additional testing of CA 50 and elastase 1. With regard to CA 125 in 11% of CF patients, 5% of control persons and 5% of parents CA 125 levels ranged above 35 U/ml. The determination of saliva CA 19-9 and CA 125 does not yield further information. Taking all previous findings into account elastase 1 is a better marker for acute pancreatitis than for pancreatic cancer and CF.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of anions on the Na(+)-H+ exchange of trout red blood cells.

1. Replacement of chloride by foreign anions in the suspending medium of trout erythrocytes can affect in a complex manner both the activation by catecholamines of the latent Na(+)-H+ exchanger and its subsequent desensitization. These changes are discussed in relation to other cellular modifications (distribution of permeant anions and accumulation of cyclic AMP) induced by foreign anions. 2. The transfer of trout erythrocytes from a chloride-containing medium to media containing lyophilic permeable anions, NO3- or SCN-, immediately induces a decrease of distribution ratios of permeable anions across the red cell membrane (i.e. Donnan ratios). It is probable that the binding of lyophilic anions to haemoglobin, by altering the amount of negative fixed charges, results in changes of distribution of permeant anions across the membrane. 3. The effectiveness of anions in decreasing both the activation of the Na(+)-H+ exchanger and the Donnan ratio follows the same sequence in both cases, i.e., SCN- greater than NO3- greater than Cl- = propionate. It was demonstrated that a change in Donnan ratio affects antiport activity possibly through a shift in intracellular pH; such a mechanism however cannot account for all the effects of foreign anions on antiport activity. 4. The present results show that lyophilic anions do not modify the affinity of the antiporter for sodium ions but greatly decrease the transport capacity of the exchange system. This is interpreted as indicating that the binding of lyophilic anions to some component of the transport system prevents antiporters from establishing their activated configuration once stimulated. Since the inhibitory effect of anions on Na(+)-H+ exchange has been demonstrated in all erythrocytes studied but in no other cell, the crucial substance involved in this inhibition could well be haemoglobin, which appears to control antiport activity in erythrocytes. 5. Some anions affect desensitization of the exchanger. This effect is not related to the lyophilic character of the anion and is not mediated by a change in intracellular cyclic AMP. 6. Propionate and acetate drastically reduce the intracellular level of cyclic AMP and seem to facilitate the activated configuration of the exchanger.

Reconstitution of the erythrocyte anion transport system: recent progress.

The anion transport system of the human erythrocyte membrane was reconstituted in phosphatidylcholine vesicles by a new procedure. The reconstituted system shows all major properties of the sulfate transport system found in the erythrocyte membrane (Scheuring, U., K. Kollewe, W. Haase, and D. Schubert: J. Membrane Biol. 90, 123-135 (1986)). Modifications of the reconstitution method have now led to increased values of the internal volumes of the protein-lipid vesicles and of the average turnover number of the transport protein (which is now larger than in the erythrocyte membrane). Gel filtration on Sephacryl S-1000 has allowed the isolation of vesicles of a narrow size distribution.