Action potentials and ion conductances in wild-type and CALHM1-knockout type II taste cells.

Taste bud type II cells fire action potentials in response to tastants, triggering nonvesicular ATP release to gustatory neurons via voltage-gated CALHM1-associated ion channels. Whereas CALHM1 regulates mouse cortical neuron excitability, its roles in regulating type II cell excitability are unknown. In this study, we compared membrane conductances and action potentials in single identified TRPM5-GFP-expressing circumvallate papillae type II cells acutely isolated from wild-type (WT) and Calhm1 knockout (KO) mice. The activation kinetics of large voltage-gated outward currents were accelerated in cells from Calhm1 KO mice, and their associated nonselective tail currents, previously shown to be highly correlated with ATP release, were completely absent in Calhm1 KO cells, suggesting that CALHM1 contributes to all of these currents. Calhm1 deletion did not significantly alter resting membrane potential or input resistance, the amplitudes and kinetics of Na+ currents either estimated from action potentials or recorded from steady-state voltage pulses, or action potential threshold, overshoot peak, afterhyperpolarization, and firing frequency. However, Calhm1 deletion reduced the half-widths of action potentials and accelerated the deactivation kinetics of transient outward currents, suggesting that the CALHM1-associated conductance becomes activated during the repolarization phase of action potentials.NEW & NOTEWORTHY CALHM1 is an essential ion channel component of the ATP neurotransmitter release mechanism in type II taste bud cells. Its contribution to type II cell resting membrane properties and excitability is unknown. Nonselective voltage-gated currents, previously associated with ATP release, were absent in cells lacking CALHM1. Calhm1 deletion was without effects on resting membrane properties or voltage-gated Na+ and K+ channels but contributed modestly to the kinetics of action potentials.

Lack of influence of DAT1 and DRD2 gene variants on antidepressant response in generalized anxiety disorder.

OBJECTIVE: Although antidepressant drugs are used as first-line intervention to treat patients with generalized anxiety disorder (GAD), only one-third of patients respond positively to treatment. In our study, we investigated whether functional genetic polymorphisms in the dopamine active transporter 1 (DAT1) and dopamine receptor D2 (DRD2) may play a role in antidepressant treatment response in GAD. METHODS: We examined 156 patients diagnosed with GAD who received venlafaxine Extended-Release (XR) treatment as part of an 18-month relapse-prevention study to determine whether variation in these genes had an effect on treatment response after 6 months of open-label treatment. Genotypes were obtained for rs1076560 (DRD2), rs1800497 (DRD2), rs2550948 (DAT1), and a variable number tandem repeat in the 3' untranslated region of the DAT1 gene using standard methods. RESULTS: Results show that none of the tested variants were associated with treatment response to venlafaxine XR in GAD. Genotype and allele frequencies did not differ statistically significantly between responders and non-responders using either the Hamilton Anxiety or Clinical Global Impressions of Improvement Scale at 6 months. CONCLUSIONS: Although we detected no association in our sample, future studies using larger samples and more comprehensive gene coverage are needed to evaluate potential effects of dopaminergic variants on antidepressant treatment response in anxiety disorders.

Identification of CHRNA5 rare variants in African-American heavy smokers.

BACKGROUND: The common CHRNA5 mis-sense coding single-nucleotide polymorphism (SNP) rs16969968:G>A (D398N) has repeatedly been shown to confer risk for heavy smoking in individuals who carry the 'A' allele (encoding the 398N amino acid). The mis-sense SNP has a minor allele frequency of ∼40% in European-Americans, but only ∼7% in African-Americans (http://www.ncbi.nlm.nih.gov/projects/SNP/). We reasoned that there might be other mis-sense variants among African-Americans that could confer the heavy smoking phenotype (defined here as ≥20 cigarettes per day), perhaps in a manner similar to that of the D398N polymorphism in Europeans. MATERIALS AND METHODS: As such, we resequenced 250 African-American heavy smokers, most of whom were homozygous 'G' at rs16969968:G>A (minor allele frequency of 9.6% within the population). RESULTS: Although many novel coding SNPs were not observed, we report an interesting, although rare (perhaps personal), variant in CHRNA5 that could result in nonsense-mediated decay of the aberrant transcript. CONCLUSION: We conclude that, in African-Americans, variants (common or rare) in genes other than CHRNA5 most likely contribute toward the nicotine-dependent phenotype, either independently or in combination with variants in CHRNA5. The functional significance, on CHRNA5 expression or protein function, of the variants found here should be determined in future studies.