Purinergic Calcium Signaling and Calcium-Activated Chloride Channels in the Supporting Cells of the Peripheral Olfactory Systems

This study is divided in three individual projects focusing on calcium signaling on nonneuronal cells of different peripheral olfactory systems. In particular, I investigated (1) the role of calcium-activated chloride channel TMEM16A in the development of the mouse olfactory epithelium, (2) the functional role of TMEM16A of mouse olfactory epithelium and (3) purinergic receptor mediated calcium signaling in the supporting cells of the vomeronasal organ (VNO). Previous reports showed that TMEM16A is expressed in the olfactory epithelium, where it localizes at the apical surface of supporting cells, more specifically, in their microvilli. To understand the role of TMEM16A on the development of the mouse olfactory epithelium we conducted the first immunohistochemistry study comparing the morphological properties of the olfactory epithelium and nasal glands in TMEM16A wild-type and knockout littermate mice. The genetic ablation of TMEM16A did not affect the maturation of olfactory sensory neurons and the morphology of the ciliary structures. In addition, TMEM16A knockout did not significantly affect the morphology of supporting cells. The average number of supporting cells, olfactory sensory neurons, horizontal and globose basal cells were not significantly different in the two mice models. These results indicate that the genetic ablation of TMEM16A does not affect the development of the olfactory epithelium. To further understand the functional role of TMEM16A, we investigated the presence of calcium-activated chloride currents in the supporting cells of the olfactory epithelium. Whole-cell patch clamp recordings from TMEM16A wild-type and knockout mice showed that the supporting cells of olfactory epithelium had a calcium-activated chloride current that was abolished in TMEM16A knockout mice. Moreover, we found that this calcium-activated currents can also be activated after the stimulation of the cells with ATP, in line with previous reports showing that supporting cells of mouse olfactory epithelium express purinergic receptors. Although the expression of purinergic receptors in supporting cells in the mouse olfactory epithelium is well documented, the expression of these receptors in mouse VNO is still unknown. Here, we conducted the first study in mouse VNO showing that vomeronasal supporting cells also express purinergic ATP receptors. Using confocal calcium imaging recording we found that a large subset of these cells, about 75%, expressed metabotropic purinergic receptors, and a smaller subset of cells, 38%, expressing P2Y2 and/or P2Y4 receptors.