Voltage-gated channel properties of epithelial cells in porcine vomeronasal organ

Somatic ion channels and action potentials in olfactory receptor cells and vomeronasal receptor cells

Olfactory receptor cells are primary sensory neurons that catch odor molecules in the olfactory system, and vomeronasal receptor cells catch pheromones in the vomeronasal system. When odor or pheromone molecules bind to receptor proteins expressed on the membrane of the olfactory cilia or vomeronasal microvilli, receptor potentials are generated in their receptor cells. This initial excitation is transmitted to the soma via dendrites, and action potentials are generated in the soma and/or axon and transmitted to the central nervous system. Thus, olfactory and vomeronasal receptor cells play an important role in converting chemical signals into electrical signals. In this review, the electrophysiological characteristics of ion channels in the somatic membrane of olfactory receptor cells and vomeronasal receptor cells in various species are described and the differences between the action potential dynamics of olfactory receptor cells and vomeronasal receptor cells are compared.

Sodium channels enable fast electrical signaling and regulate phagocytosis in the retinal pigment epithelium

BACKGROUND

Voltage-gated sodium (Nav) channels have traditionally been considered a trademark of excitable cells. However, recent studies have shown the presence of Nav channels in several non-excitable cells, such as astrocytes and macrophages, demonstrating that the roles of these channels are more diverse than was previously thought. Despite the earlier discoveries, the presence of Nav channel-mediated currents in the cells of retinal pigment epithelium (RPE) has been dismissed as a cell culture artifact. We challenge this notion by investigating the presence and possible role of Nav channels in RPE both ex vivo and in vitro.

RESULTS

Our work demonstrates that several subtypes of Nav channels are found in human embryonic stem cell (hESC)-derived and mouse RPE, most prominently subtypes Nav1.4, Nav1.6, and Nav1.8. Whole cell patch clamp recordings from the hESC-derived RPE monolayers showed that the current was inhibited by TTX and QX-314 and was sensitive to the selective blockers of the main Nav subtypes. Importantly, we show that the Nav channels are involved in photoreceptor outer segment phagocytosis since blocking their activity significantly reduces the efficiency of particle internalization. Consistent with this role, our electron microscopy results and immunocytochemical analysis show that Nav1.4 and Nav1.8 accumulate on phagosomes and that pharmacological inhibition of Nav channels as well as silencing the expression of Nav1.4 with shRNA impairs the phagocytosis process.

CONCLUSIONS

Taken together, our study shows that Nav channels are present in RPE, giving this tissue the capacity of fast electrical signaling. The channels are critical for the physiology of RPE with an important role in photoreceptor outer segment phagocytosis.

Ascl1 (Mash1) knockout perturbs differentiation of nonneuronal cells in olfactory epithelium

The embryonic olfactory epithelium (OE) generates only a very few olfactory sensory neurons when the basic helix-loop-helix transcription factor, ASCL1 (previously known as MASH1) is eliminated by gene mutation. We have closely examined the structure and composition of the OE of knockout mice and found that the absence of neurons dramatically affects the differentiation of multiple other epithelial cell types as well. The most prominent effect is observed within the two known populations of stem and progenitor cells of the epithelium. The emergence of horizontal basal cells, a multipotent progenitor population in the adult epithelium, is anomalous in the Ascl1 knockout mice. The differentiation of globose basal cells, another multipotent progenitor population in the adult OE, is also aberrant. All of the persisting globose basal cells are marked by SOX2 expression, suggesting a prominent role for SOX2 in progenitors upstream of Ascl1. However, NOTCH1-expressing basal cells are absent from the knockout; since NOTCH1 signaling normally acts to suppress Ascl1 via HES1 and drives sustentacular (Sus) cell differentiation during adult epithelial regeneration, its absence suggests reciprocity between neurogenesis and the differentiation of Sus cells. Indeed, the Sus cells of the mutant mice express a markedly lower level of HES1, strengthening that notion of reciprocity. Duct/gland development appears normal. Finally, the expression of cKIT by basal cells is also undetectable, except in those small patches where neurogenesis escapes the effects of Ascl1 knockout and neurons are born. Thus, persistent neurogenic failure distorts the differentiation of multiple other cell types in the olfactory epithelium.