The simplest cell-like structure, the lipid bilayer vesicle, can respond to mechanical deformation by elastic membrane dilation/thinning and curvature changes. When a protein is inserted in the lip...

Molecular basis of mechanotransduction in living cells

In mechanosensitive (MS) channels, gating is initiated by changes in intra-bilayer pressure profiles originating from bilayer deformation. Here we evaluated two physical mechanisms as triggers of MS channel gating: the energetic cost of protein-bilayer hydrophobic mismatches and the geometric consequences of bilayer intrinsic curvature. Structural changes in the Escherichia coli large MS channel (MscL) were studied under nominally zero transbilayer pressures using both patch clamp and EPR spectroscopic approaches. Changes in membrane intrinsic curvature induced by the external addition of lysophosphatidylcholine (LPC) generated massive spectroscopic changes in the narrow constriction that forms the channel 'gate', trapping the channel in the fully open state. Hydrophobic mismatch alone was unable to open the channel, but decreasing bilayer thickness lowered MscL activation energy, stabilizing a structurally distinct closed channel intermediate. We propose that the mechanism of mechanotransduction in MS channels is defined by both local and global asymmetries in the transbilayer pressure profile at the lipid-protein interface.

Physical principles underlying the transduction of bilayer deformation forces during mechanosensitive channel gating

P2X receptors are cation channels gated by extracellular ATP The seven known P2X isoforms possess no sequence homology with other proteins Here we studied the quaternary structure of P2X receptors by chemical cross-linking and blue native PAGE P2X1 and P2X3 were N-terminally tagged with six histidine residues to allow for non-denaturing receptor isolation from cRNA-injected, [35S]methionine-labeled oocytes The His-tag did not change the electrophysiological properties of the P2X1 receptor His-P2X1 was found to carry four N-glycans per polypeptide chain, only one of which acquired Endo H resistance en route to the plasma membrane 3, 3'-Dithiobis(sulfosuccinimidylpropionate) (DTSSP) and two of three bifunctional analogues of the P2X receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) cross-linked digitonin-solubilized His-P2X1 and His-P2X3 quantitatively to homo-trimers Likewise, when analyzed by blue native PAGE, P2X receptors purified in digitonin or dodecyl-beta-D-maltoside migrated entirely as non-covalently linked homo-trimers, whereas the alpha2 beta gamma delta nicotinic acetylcholine receptor (used as a positive control) migrated as the expected pentamer P2X monomers remained undetected soon after synthesis, indicating that trimerization occurred in the endoplasmic reticulum The plasma membrane form of His-P2X1 was also identified as a homo-trimer If n-octylglucoside was used for P2X receptor solubilization, homo-hexamers were observed, suggesting that trimers can aggregate to form larger complexes We conclude that trimers represent an essential element of P2X receptor structure Keywords: blue native PAGE/cross-linking/P2X receptor/quaternary structure

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P2X1 and P2X3 receptors form stable trimers: a novel structural motif of ligand-gated ion channels.

Mechanosensitive channels act as membrane-embedded mechano-electrical switches, opening a large water-filled pore in response to lipid bilayer deformations. This process is critical to the response of living organisms to direct physical stimulation, such as in touch, hearing and osmoregulation. Here, we have determined the structural rearrangements that underlie these events in the large prokaryotic mechanosensitive channel (MscL) using electron paramagnetic resonance spectroscopy and site-directed spin labelling. MscL was trapped in both the open and in an intermediate closed state by modulating bilayer morphology. Transition to the intermediate state is characterized by small movements in the first transmembrane helix (TM1). Subsequent transitions to the open state are accompanied by massive rearrangements in both TM1 and TM2, as shown by large increases in probe dynamics, solvent accessibility and the elimination of all intersubunit spin-spin interactions. The open state is highly dynamic, supporting a water-filled pore of at least 25 A, lined mostly by TM1. These structures suggest a plausible molecular mechanism of gating in mechanosensitive channels.

Open channel structure of MscL and the gating mechanism of mechanosensitive channels

Mechanosensitive channels act as membrane-embedded mechano-electrical switches, opening a large water-filled pore in response to lipid bilayer deformations. This process is critical to the response of living organisms to direct physical stimulation, such as in touch, hearing and osmoregulation. Here, we have determined the structural rearrangements that underlie these events in the large prokaryotic mechanosensitive channel (MscL) using electron paramagnetic resonance spectroscopy and site-directed spin labelling. MscL was trapped in both the open and in an intermediate closed state by modulating bilayer morphology. Transition to the intermediate state is characterized by small movements in the first transmembrane helix (TM1). Subsequent transitions to the open state are accompanied by massive rearrangements in both TM1 and TM2, as shown by large increases in probe dynamics, solvent accessibility and the elimination of all intersubunit spin‐spin interactions. The open state is highly dynamic, supporting a water-filled pore of at least 25 A ˚ , lined mostly by TM1. These structures suggest a plausible molecular mechanism of gating in mechanosensitive channels.

Open channel structure of MscL and the gating mechanism of mechanosensitive

Aims To examine the literature regarding clinical pharmacokinetics, direct effects and adverse clinical outcomes associated with methamphetamine use.

Methods  Relevant literature was identified through a PubMed search. Additional literature was obtained from relevant books and monographs.

Findings and conclusions  The mean elimination half-life for methamphetamine is approximately 10 hours, with considerable inter-individual variability in pharmacokinetics. Direct effects at low-to-moderate methamphetamine doses (5–30 mg) include arousal, positive mood, cardiac stimulation and acute improvement in cognitive domains such as attention and psychomotor coordination. At higher doses used typically by illicit users (≥50 mg), methamphetamine can produce psychosis. Its hypertensive effect can produce a number of acute and chronic cardiovascular complications. Repeated use may induce neurotoxicity, associated with prolonged psychiatric symptoms, cognitive impairment and an increased risk of developing Parkinson's disease. Abrupt cessation of repeated methamphetamine use leads to a withdrawal syndrome consisting of depressed mood, anxiety and sleep disturbance. Acute withdrawal lasts typically for 7–10 days, and residual symptoms associated with neurotoxicity may persist for several months.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1360-0443.2009.02564.x

A review of the clinical pharmacology of methamphetamine.

Estimation of the pore size of the large-conductance mechanosensitive ion channel of Escherichia coli

Introduction and Aims. As an antidepressant with sedative and anxiolytic properties, mirtazapine may be an appropriate pharmacotherapy for methamphetamine withdrawal. This study sought to examine whether mirtazapine improves retention and alleviates methamphetamine withdrawal symptoms in an out-patient setting. Design and Methods. An out-patient double-blind, randomised placebo-controlled trial of mirtazapine for the treatment of methamphetamine withdrawal was conducted (15 mg nocte for 2 days, 30 mg nocte for 12 days). Both groups were offered narrative therapy counselling. Measures recorded on days 0, 3, 7, 14 and 35 included: treatment retention, Amphetamine Cessation Symptoms Assessment, the Athens Insomnia Scale, the Brief Symptom Inventory, the Depression – Anxiety – Stress Scale (DASS), Severity of Dependence scale and the Opiate Treatment Index Drug Use subscale. Results. Thirty-one participants were recruited (18 placebo, 13 mirtazapine) and 52% completed the 2-week medication phase. No significa...

https://onlinelibrary.wiley.com/doi/pdf/10.1080/09595230801935672

A placebo-controlled trial of mirtazapine for the management of methamphetamine withdrawal.

The Impact of Online Lecture Recordings on Learning Outcomes in Pharmacology

Amphetamines are second to cannabis as the most prevalent illicit drug used in Australia, and amphetamine abuse and dependence are associated with significant health and psychosocial harms. The current paper presents a series of studies investigating the prevalence of depression and other psychological problems among Western Australian patients receiving treatment for methamphetamine dependence. In the first study, a medical case-note audit explored the psychological profile among 218 consecutive admissions to an inpatient methamphetamine detoxification program. In the second study, the Beck Depression Inventory (BDI-II, Beck, Steer, & Brown, 1996) was administered to 367 patients receiving outpatient treatment for methamphetamine or heroin dependence (Phase 1), and the relationship between scores on the BDI-II and methamphetamine intoxication was explored (Phase 2). High rates of depression and other psychological problems were identified. Approximately 46% of methamphetamine-dependent individuals enteri...

Depression and other psychological health problems among methamphetamine dependent patients in treatment: Implications for assessment and treatment outcome

Chris Cruickshank

Papers

A review of the clinical pharmacology of methamphetamine.

Estimation of the pore size of the large-conductance mechanosensitive ion channel of Escherichia coli

A placebo-controlled trial of mirtazapine for the management of methamphetamine withdrawal.

The Impact of Online Lecture Recordings on Learning Outcomes in Pharmacology

Depression and other psychological health problems among methamphetamine dependent patients in treatment: Implications for assessment and treatment outcome