Multidrug resistance protein MdtM adds to the repertoire of antiporters involved in alkaline pH homeostasis in <em>Escherichia coli</em>

BACKGROUND: In neutralophilic bacteria, monovalent metal cation/H(+) antiporters play a key role in pH homeostasis. In Escherichia coli, only four antiporters (NhaA, NhaB, MdfA and ChaA) are identified to function in maintenance of a stable cytoplasmic pH under conditions of alkaline stress. We hypothesised that the multidrug resistance protein MdtM, a recently characterised homologue of MdfA and a member of the major facilitator superfamily, also functions in alkaline pH homeostasis. RESULTS: Assays that compared the growth of an E. coli ΔmdtM deletion mutant transformed with a plasmid encoding wild-type MdtM or the dysfunctional MdtM D22A mutant at different external alkaline pH values (ranging from pH 8.5 to 10) revealed a potential contribution by MdtM to alkaline pH tolerance, but only when millimolar concentrations of sodium or potassium was present in the growth medium. Fluorescence-based activity assays using inverted vesicles generated from transformants of antiporter-deficient (ΔnhaA, ΔnhaB, ΔchaA) E. coli TO114 cells defined MdtM as a low-affinity antiporter that catalysed electrogenic exchange of Na(+), K(+), Rb(+) or Li(+) for H(+). The K(+)/H(+) antiport reaction had a pH optimum at 9.0, whereas the Na(+)/H(+) exchange activity was optimum at pH 9.25. Measurement of internal cellular pH confirmed MdtM as contributing to maintenance of a stable cytoplasmic pH, acid relative to the external pH, under conditions of alkaline stress. CONCLUSIONS: Taken together, the results support a role for MdtM in alkaline pH tolerance. MdtM can therefore be added to the currently limited list of antiporters known to function in pH homeostasis in the model organism E. coli

Behavioral and Physiological Effects of a Novel Kappa-Opioid Receptor-Based DREADD in Rats

In the past decade, novel methods using engineered receptors have enabled researchers to manipulate neuronal activity with increased spatial and temporal specificity. One widely used chemogenetic method in mice and rats is the DREADD (designer receptors exclusively activated by designer drugs) system in which a mutated muscarinic G protein-coupled receptor is activated by an otherwise inert synthetic ligand, clozapine-N-oxide (CNO). Recently, the Roth laboratory developed a novel inhibitory DREADD in which a mutated kappa-opioid receptor (KORD) is activated by the pharmacologically inert drug salvinorin B (SalB; Vardy et al, 2015). They demonstrated the feasibility of using KORD to study brain circuits involved in motivated behavior in mice. Here, we used behavioral, electrophysiological, and neuroanatomical methods to demonstrate the feasibility of using the novel KORD to study brain circuits involved in motivated behavior in rats. In Exp. 1, we show that SalB dose-dependently decreased spontaneous and cocaine-induced locomotor activity in rats expressing KORD to midbrain (ventral tegmental area/substantia nigra). In Exp. 2, we show that SalB completely inhibited tonic firing in KORD-expressing putative dopamine neurons in midbrain. In Exp. 3, we used a 'retro-DREADD' dual-virus approach to restrict expression of KORD in ventral subiculum neurons that project to nucleus accumbens shell. We show that KORD activation selectively decreased novel context-induced Fos expression in this projection. Our results indicate that the novel KORD is a promising tool to selectively inactivate brain areas and neural circuits in rat studies of motivated behavior

The relationship between eligibility criteria and adverse events in randomized controlled trials of hematologic malignancies

To minimize adverse events (AEs) unrelated to drugs and maximize the likelihood of drug approvals, eligibility criteria for randomized controlled trials (RCTs) may be overly restrictive. The purpose of this study was to determine if RCTs in hematologic malignancies exclude patients irrespective of known toxicities or observed AEs. MEDLINE was searched from 1/2010 to 1/2015 for RCTs published in high-impact journals. Of 97 trials, 33% were conducted in leukemia, 28% in lymphoma, 34% in multiple myeloma and 5% in myelodysplastic syndromes or myelofibrosis. Expected toxicities at thresholds of ⩾10%, ⩾5% and <5% were not correlated with cardiac, hepatic or renal eligibility criteria (logistic regression). To explore this lack of correlation we tested the concordance of expected toxicities and eligibility criteria using a modified version of McNemar's test: at each threshold, hepatic, renal and cardiac expected toxicities were significantly discordant with eligibility criteria. Hepatic and renal eligibility criteria were also not correlated with observed AEs, P=0.69 and P=0.77, respectively, but a significant correlation was detected between cardiac eligibility criteria and observed AEs, P=0.02. Thus, the analyzed RCTs excluding patients with organ dysfunction do not reflect expected toxicities, based on prescription drug labels/prior experience, or reported AEs on the trials