Ca2+-activated Cl- currents in the murine vomeronasal organ enhance neuronal spiking but are dispensable for male-male aggression.

Ca2+-activated Cl- currents have been observed in many physiological processes, including sensory transduction in mammalian olfaction. The olfactory vomeronasal (or Jacobson's) organ (VNO) detects molecular cues originating from animals of the same species or from predators. It then triggers innate behaviors such as aggression, mating, or flight. In the VNO, Ca2+-activated Cl- channels (CaCCs) are thought to amplify the initial pheromone-evoked receptor potential by mediating a depolarizing Cl- efflux. Here, we confirmed the co-localization of the Ca2+-activated Cl- channels anoctamin 1 (Ano1, also called TMEM16A) and Ano2 (TMEM16B) in microvilli of apically and basally located vomeronasal sensory neurons (VSNs) and their absence in supporting cells of the VNO. Both channels were expressed as functional isoforms capable of giving rise to Ca2+-activated Cl- currents. Although these currents persisted in the VNOs of mice lacking Ano2, they were undetectable in olfactory neuron-specific Ano1 knockout mice irrespective of the presence of Ano2 The loss of Ca2+-activated Cl- currents resulted in diminished spontaneous and drastically reduced pheromone-evoked spiking of VSNs. Although this indicated an important role of anoctamin channels in VNO signal amplification, the lack of this amplification did not alter VNO-dependent male-male territorial aggression in olfactory Ano1/Ano2 double knockout mice. We conclude that Ano1 mediates the bulk of Ca2+-activated Cl- currents in the VNO and that Ano2 plays only a minor role. Furthermore, vomeronasal signal amplification by CaCCs appears to be dispensable for the detection of male-specific pheromones and for near-normal aggressive behavior in mice.

Identification of LRRC8 heteromers as an essential component of the volume-regulated anion channel VRAC.

Regulation of cell volume is critical for many cellular and organismal functions, yet the molecular identity of a key player, the volume-regulated anion channel VRAC, has remained unknown. A genome-wide small interfering RNA screen in mammalian cells identified LRRC8A as a VRAC component. LRRC8A formed heteromers with other LRRC8 multispan membrane proteins. Genomic disruption of LRRC8A ablated VRAC currents. Cells with disruption of all five LRRC8 genes required LRRC8A cotransfection with other LRRC8 isoforms to reconstitute VRAC currents. The isoform combination determined VRAC inactivation kinetics. Taurine flux and regulatory volume decrease also depended on LRRC8 proteins. Our work shows that VRAC defines a class of anion channels, suggests that VRAC is identical to the volume-sensitive organic osmolyte/anion channel VSOAC, and explains the heterogeneity of native VRAC currents.