Cell-surface receptors for gibbon ape leukemia virus and amphotropic murine retrovirus are inducible sodium-dependent phosphate symporters.

Cell surface receptors for gibbon ape leukemia virus (Glvr-1) and murine amphotropic retrovirus (Ram-1) are distinct but related proteins having multiple membrane-spanning regions. Distant homology with a putative phosphate permease of Neurospora crassa suggested that these receptors might serve transport functions. By expression in Xenopus laevis oocytes and in mammalian cells, we have identified Glvr-1 and Ram-1 as sodium-dependent phosphate symporters. Two-electrode voltage-clamp analysis indicates net cation influx, suggesting that phosphate is transported with excess sodium ions. Phosphate uptake was reduced by > 50% in mouse fibroblasts expressing amphotropic envelope glycoprotein, which binds to Ram-1, indicating that Ram-1 is a major phosphate transporter in these cells. RNA analysis shows wide but distinct tissue distributions, with Glvr-1 expression being highest in bone marrow and Ram-1 in heart. Overexpression of Ram-1 severely repressed Glvr-1 synthesis in fibroblasts, suggesting that transporter expression may be controlled by net phosphate accumulation. Accordingly, depletion of extracellular phosphate increased Ram-1 and Glvr-1 expression 3- to 5-fold. These results suggest simple methods to modulate retroviral receptor expression, with possible applications to human gene therapy.     

Interaction of ritonavir-boosted tipranavir with loperamide does not result in loperamide-associated neurologic side effects in healthy volunteers

Loperamide (LOP) is a peripherally acting opioid receptor agonist used for the management of chronic diarrhea through the reduction of gut motility. The lack of central opioid effects is partly due to the efflux activity of the multidrug resistance transporter P-glycoprotein (P-gp) at the blood-brain barrier. The protease inhibitors are substrates for P-gp and have the potential to cause increased LOP levels in the brain. Because protease inhibitors, including tipranavir (TPV), are often associated with diarrhea, they are commonly used in combination with LOP. The level of respiratory depression, the level of pupil constriction, the pharmacokinetics, and the safety of LOP alone compared with those of LOP-ritonavir (RTV), LOP-TPV, and LOP-TPV-RTV were evaluated in a randomized, open-label, parallel-group study with 24 healthy human immunodeficiency virus type 1-negative adults. Respiratory depression was assessed by determination of the ventilatory response to carbon dioxide. Tipranavir-containing regimens (LOP-TPV and LOP-TPV-RTV) caused decreases in the area under the concentration-time curve from time zero to infinity for LOP (51% and 63% decreases, respectively) and its metabolite (72% and 77% decreases, respectively), whereas RTV caused increases in the levels of exposure of LOP (121% increase) and its metabolite (44% increase). In vitro and in vivo data suggest that TPV is a substrate for and an inducer of P-gp activity. The respiratory response to LOP in combination with TPV and/or RTV was not different from that to LOP alone. There was no evidence that LOP had opioid effects in the central nervous system, as measured indirectly by CO2 response curves and pupillary response in the presence of TPV and/or RTV.     

Recurrence of atrial tachyarrhythmias in implantable cardioverter-defibrillator recipients

BACKGROUND: Because the natural history of atrial tachyarrhythmia (AT) is not known in patients with implantable cardioverter-defibrillators (ICDs) but without device-based atrial therapies, we aimed to describe the characteristics and recurrence of AT in such patients. METHODS: In this multicenter trial, 269 patients with standard indications for ICD placement and 2 episodes of AT in the preceding year received a dual-chamber ICD capable of logging AT. Patients were randomly assigned to 3-month periods of atrial therapies "on" or "off." This analysis considered only the 118 patients with atrial therapies programmed off at ICD placement. RESULTS: Fifty-eight patients (49%) had at least 1 AT episode longer than 1 minute, and 21 (18%) had at least 1 prolonged episode (>24 hours). The median episode frequency for each patient (episodes per month) was 1.8 episodes longer than 1 minute, 0.8 longer than 1 hour, and 0 longer than 24 hours. The median AT burden was 12.2 hours per month. CONCLUSIONS: Patients with standard ICD indications and history of AT have infrequent episodes, frequent short episodes, or prolonged episodes of AT-atrial fibrillation. However, the clinical characteristics examined did not distinguish among the groups. Improved diagnostic tools may help identify patients at risk for development of AT, thereby allowing specific therapies to be targeted to each group of patients.     

Factors affecting rheumatoid arthritis patients' decisions to participate in clinical trials

OBJECTIVE: To delineate the personal, psychosocial, and disease-related factors that may influence rheumatoid arthritis (RA) patients' decisions to participate in clinical trials. METHODS: A total of 191 patients with RA were asked to participate in this survey. The questionnaire collected information on demographics, RA disease-related factors, and the importance of several factors that might influence patients' willingness to participate in clinical trials. Patients were then asked if they would consider participating in a hypothetical study. RESULTS: Participants were 88% female with a mean age of 40.5 years. The ethnic composition was 57% Hispanic, 25% Caucasian, 12% Asian, and 6% African American, with 71% having a family income < $20,000/year. Factors that patients considered important for participation in a clinical study included: the opportunity to help others, the possibility of improved health, early access to new therapy, the availability of free treatments, unknown side effects of the study drug, and the need to stop current therapy. There were strong correlations between the rank order importance weights between Hispanics and Caucasians, suggesting fundamental similarities in preferences. The most important factor was the opportunity to help others. In general, the more important factors were associated with preferences for trial participation. CONCLUSION: This questionnaire identified factors that may affect RA patients' willingness to participate in a study. Patient participation in trials is driven by diverse factors that include altruism and the opportunity for healthcare and improved health. Consideration of these factors may facilitate the inclusion of more diverse patient populations into trials and enhance the applicability of trial results.     

Fluorometric measurements of conformational changes in glutamate transporters

Glutamate transporters remove glutamate from the synaptic cleft to maintain efficient synaptic communication between neurons and to prevent extracellular glutamate concentrations from reaching neurotoxic levels (1). It is thought that glutamate transporters mediate glutamate transport through a reaction cycle with conformational changes between the two major access states that alternatively expose glutamate-binding sites to the extracellular or to the intracellular solution. However, there is no direct real-time evidence for the conformational changes predicted to occur during the transport cycle. In the present study, we used voltage-clamp fluorometry to measure conformational changes in the neuronal excitatory amino acid transporter (EAAT) 3 glutamate transporter covalently labeled with a fluorescent reporter group. Alterations in glutamate and cotransported ion concentrations or in the membrane voltage induced changes in the fluorescence that allowed detection of conformational rearrangements occurring during forward and reverse transport. In addition to the transition between the two major access states, our results show that there are significant Na(+)-dependent conformational changes preceding glutamate binding. We furthermore show that Na(+) and H(+) are cotransported with glutamate in the forward part of the transport cycle. The data further suggest that an increase in proton concentrations slows the reverse transport of glutamate, which may play a neuro-protective role during ischemia.     

A randomized trial comparing digital and live lecture formats [ISRCTN40455708

Background  

Medical education is increasingly being conducted in community-based teaching sites at diverse locations, making it difficult to provide a consistent curriculum. We conducted a randomized trial to assess whether students who viewed digital lectures would perform as well on a measure of cognitive knowledge as students who viewed live lectures. Students' perceptions of the digital lecture format and their opinion as whether a digital lecture format could serve as an adequate replacement for live lectures was also assessed.     

Role of tumour necrosis factor gene polymorphisms (-308 and -238) in breast cancer susceptibility and severity

Introduction  

Genetic polymorphisms in the promoter region of the tumour necrosis factor (TNF) gene can regulate gene expression and have been associated with inflammatory and malignant conditions. We have investigated two polymorphisms in the promoter of the TNF gene (-308 G>A and -238 G>A) for their role in breast cancer susceptibility and severity by means of an allelic association study.