Characterization of DAG binding to TRPC channels by target-dependent cis–trans isomerization of OptoDArG

Azobenzene-based photochromic lipids are valuable probes for the analysis of ion channel–lipid interactions. Rapid photoisomerization of these molecules enables the analysis of lipid gating kinetics and provides information on lipid sensing. Thermal relaxation of the metastable cis conformation to the trans conformation of azobenzene photolipids is rather slow in the dark and may be modified by ligand–protein interactions. Cis photolipid-induced changes in pure lipid membranes as visualized from the morphological response of giant unilamellar vesicles indicated that thermal cis–trans isomerization of both PhoDAG-1 and OptoDArG is essentially slow in the lipid bilayer environment. While the currents activated by cis PhoDAG remained stable upon termination of UV light exposure (dark, UV-OFF), cis OptoDArG-induced TRPC3/6/7 activity displayed a striking isoform-dependent exponential decay. The deactivation kinetics of cis OptoDArG-induced currents in the dark was sensitive to mutations in the L2 lipid coordination site of TRPC channels. We conclude that the binding of cis OptoDArG to TRPC channels promotes transition of cis OptoDArG to the trans conformation. This process is suggested to provide valuable information on DAG–ion channel interactions and may enable highly selective photopharmacological interventions

Engineering the Photoresponse of InAs Nanowires

We report on individual-InAs nanowire optoelectronic devices which can be tailored to exhibit either negative or positive photoconductivity (NPC or PPC). The NPC photoresponse time and magnitude is found to be highly tunable by varying the nanowire diameter under controlled growth conditions. Using hysteresis characterization, we decouple the observed photoexcitation-induced hot electron trapping from conventional electric field-induced trapping to gain a fundamental insight into the interface trap states responsible for NPC. Furthermore, we demonstrate surface passivation without chemical etching which both enhances the field-effect mobility of the nanowires by approximately an order of magnitude and effectively eliminates the hot carrier trapping found to be responsible for NPC, thus restoring an "intrinsic" positive photoresponse. This opens pathways toward engineering semiconductor nanowires for novel optical-memory and photodetector applications.We acknowledge funding from the EPSRC (Grant No. EP/ M009505/1) and the ERC (Grant No. 716471, ACrossWire). S.H. acknowledges funding from the EPSRC (Grant No. EP/ P005152/1). This work was also supported by the Australian Research Council, Australian National Fabrication Facility and Australian Microscopy & Microanalysis Research Facility. J.A.A.-W. acknowledges the support of his Research Fellowships from the Royal Commission for the Exhibition of 1851 and Churchill College, Cambridge. C.K.G acknowledges the support of her scholarship from The Winston Churchill Foundation of the United States

Engineering the Photoresponse of InAs Nanowires.

We report on individual-InAs nanowire optoelectronic devices which can be tailored to exhibit either negative or positive photoconductivity (NPC or PPC). The NPC photoresponse time and magnitude is found to be highly tunable by varying the nanowire diameter under controlled growth conditions. Using hysteresis characterization, we decouple the observed photoexcitation-induced hot electron trapping from conventional electric field-induced trapping to gain a fundamental insight into the interface trap states responsible for NPC. Furthermore, we demonstrate surface passivation without chemical etching which both enhances the field-effect mobility of the nanowires by approximately an order of magnitude and effectively eliminates the hot carrier trapping found to be responsible for NPC, thus restoring an "intrinsic" positive photoresponse. This opens pathways toward engineering semiconductor nanowires for novel optical-memory and photodetector applications

The GPR55 agonist lysophosphatidylinositol acts as an intracellular messenger and bidirectionally modulates Ca2+-activated large-conductance K+ channels in endothelial cells

Lysophospholipids are known to serve as intra- and extracellular messengers affecting many physiological processes. Lysophosphatidylinositol (LPI), which is produced in endothelial cells, acts as an endogenous agonist of the orphan receptor, G protein-coupled receptor 55 (GPR55). Stimulation of GPR55 by LPI evokes an intracellular Ca2+ rise in several cell types including endothelial cells. In this study, we investigated additional direct, receptor-independent effects of LPI on endothelial large-conductance Ca2+ and voltage-gated potassium (BKCa) channels. Electrophysiological experiments in the inside-out configuration revealed that LPI directly affects the BKCa channel gating properties. This effect of LPI strictly depended on the presence of Ca2+ and was concentration-dependent, reversible, and dual in nature. The modulating effects of LPI on endothelial BKCa channels correlated with their initial open probability (Po): stimulation at low Po (<0.3) and inhibition at high Po levels (>0.3). In the whole-cell configuration, LPI in the pipette facilitated membrane hyperpolarization in response to low (0.1–2 μM) histamine concentrations. In contrast, LPI counteracted membrane hyperpolarization in response to supramaximal cell stimulation with histamine. These results highlight a novel receptor-independent and direct bidirectional modulation of BKCa channels by LPI on endothelial cells. We conclude that LPI via this mechanism serves as an important modulator of endothelial electrical responses to cell stimulation

ATP release via anion channels

ATP serves not only as an energy source for all cell types but as an ‘extracellular messenger-for autocrine and paracrine signalling. It is released from the cell via several different purinergic signal efflux pathways. ATP and its Mg2+ and/or H+ salts exist in anionic forms at physiological pH and may exit cells via some anion channel if the pore physically permits this. In this review we survey experimental data providing evidence for and against the release of ATP through anion channels. CFTR has long been considered a probable pathway for ATP release in airway epithelium and other types of cells expressing this protein, although non-CFTR ATP currents have also been observed. Volume-sensitive outwardly rectifying (VSOR) chloride channels are found in virtually all cell types and can physically accommodate or even permeate ATP4- in certain experimental conditions. However, pharmacological studies are controversial and argue against the actual involvement of the VSOR channel in significant release of ATP. A large-conductance anion channel whose open probability exhibits a bell-shaped voltage dependence is also ubiquitously expressed and represents a putative pathway for ATP release. This channel, called a maxi-anion channel, has a wide nanoscopic pore suitable for nucleotide transport and possesses an ATP-binding site in the middle of the pore lumen to facilitate the passage of the nucleotide. The maxi-anion channel conducts ATP and displays a pharmacological profile similar to that of ATP release in response to osmotic, ischemic, hypoxic and salt stresses. The relation of some other channels and transporters to the regulated release of ATP is also discussed