Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) can be caused by mutations in the neuronal nicotinic acetylcholine receptor (nAChR) subunit genes CHRNA4 and CHRNB2. Recently, a point mutation (alpha2-I279N) associated with sleep-related epilepsy has been described in a third nAChR gene, CHRNA2. We demonstrate here that alpha2-I279N can be co-expressed with the major structural subunit CHRNB2. alpha2-I279N causes a marked gain-of-function effect and displays a distinct biopharmacological profile, including markedly reduced inhibition by carbamazepine and increased nicotine sensitivity.

SUMMARY A chloride current, ICl,H, slowly activating on hyperpolarisation was investigated in Drosophila melanogaster larval muscles using the two-electrode voltage clamp. Sizeable currents were observed after the intracellular chloride concentration([Cl–]i) had been elevated by diffusion of Cl– from the electrodes. The time course of ICl,H was rather variable and required two exponentials to be accurately described. The reversal potential, –40 to –20 mV in Cl–-loaded fires, shifted on lowering external[Cl–] in the positive direction. Steady-state activation of ICl,H was characterised by V0.5 of≈–120 mV and a slope factor, k, of ≈10 mV at a[Cl–]i ≈35 mmol l–1. Raising[Cl–]i to ≈50 mmol l–1 caused a negative shift of V0.5 equivalent to the change of ECl and led to a nearly threefold increase in maximal steady-state conductance. ICl,H was resistant to 10 mmol l–1 Zn2+ and 1 mmol l–1Cd2+ but was greatly reduced by 1 mmol l–19-anthracenecarboxylic acid (9-AC). ICl,H was affected by changes of extracellular pH and increased on lowering extracellular osmolality. 9-AC also decreased muscle fibre resting conductance by approximately 20% and increased muscle contractions. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis confirmed the expression of all three ClC genes in muscle, and immunohistochemistry indicated location of Drosophila melanogaster chloride channel-2(DmClC-2) at the Z-lines. We conclude that DmClC-2 accounts for the channels underlying ICl,H, and in part for the resting chloride conductance. DmClC-2 may serve general homeostatic mechanisms such as pH- and osmo-regulation or may support muscle function on high motor activity or during a particular neurohormonal state of the animal.

BackgroundNon-coding single nucleotide polymorphisms within the nicotinic acetylcholine receptor alpha 4 subunit gene (CHRNA4) are robustly associated with various neurological and behavioral phenotypes including schizophrenia, cognition and smoking. The most commonly associated polymorphisms are located in exon 5 and segregate as part of a haplotype. So far it is unknown if this haplotype is indeed functional, or if the observed associations are an indirect effect caused by linkage disequilibrium with not yet identified adjacent functional variants. We therefore analyzed the functional relevance of the exon 5 haplotype alleles.ResultsUsing voltage clamp experiments we were able to show that the CHRNA4 haplotype alleles differ with respect to their functional effects on receptor sensitivity including reversal of receptor sensitivity between low and high acetylcholine concentrations. The results indicate that underlying mechanisms might include differences in codon usage bias and changes in mRNA stability.ConclusionsOur data demonstrate that the complementary alleles of the CHRNA4 exon 5 haplotype are functionally relevant, and might therefore be causative for the above mentioned associations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-015-0204-1) contains supplementary material, which is available to authorized users.

Muscle tension receptors in animals monitor the tension generated by muscles. This information is important for the initiation and control of movements and for muscle tone in relation to spatial orientation and gravity. Vertebrates have tendon organs located at the musculo-tendinous junction. The number of muscle fibers attached to one receptor is in the range of 3 to 25. In insects by contrast, only a few examples are known where muscle tension is measured by only single receptors embedded in the muscle. All other muscle activity is monitored by a range of other receptors that detect strains on the cuticle or movements of the joints. Here we describe a set of approximately 200 receptor cells located on a single insect muscle. These receptor cells are associated with ovipositor muscle fibers and were preferentially responsive to muscle tension and not muscle length. Although single receptors may respond differently, their summed response to altered muscle tension characterized them as phasic-tonic type receptors. Experimental activation of muscle receptors in animals producing a basic oviposition motor pattern inhibited homonymous muscle activity without resetting the phase of the rhythm. These results suggest a potential role of tension receptors in regulating ovipositor muscle activity and in particular preventing excessive muscle tension during oviposition. The muscle receptors presented here provide the first example of tension measurement in insects by a few hundred receptor cells associated with a single muscle. Their role in motor control and relation to other tension receptors in vertebrates and invertebrates are discussed.

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