title: Rat Merkel cells are mechanoreceptors and osmoreceptors.
abstract: Merkel cells (MCs) associated with nerve terminals constitute MC-neurite complexes, which are involved in slowly-adapting type I mechanoreception. Although MCs are known to express voltage-gated Ca2+ channels and hypotonic-induced membrane deformation is known to lead to Ca2+ transients, whether MCs initiate mechanotransduction is currently unknown. To answer to this question, rat MCs were transfected with a reporter vector, which enabled their identification.Their properties were investigated through electrophysiological studies. Voltage-gated K+, Ca2+ and Ca2+-activated K+ (KCa)channels were identified, as previously described. Here, we also report the activation of Ca2+ channels by histamine and their inhibition by acetylcholine. As a major finding, we demonstrated that direct mechanical stimulations induced strong inward Ca2+ currents in MCs. Depolarizations were dependent on the strength and the length of the stimulation. Moreover, touch-evoked currents were inhibited by the stretch channel antagonist gadolinium. These data confirm the mechanotransduction capabilities of MCs. Furthermore, we found that activation of the osmoreceptor TRPV4 in FM1-43-labeled MCs provoked neurosecretory granule exocytosis. Since FM1-43 blocks mechanosensory channels, this suggests that hypo-osmolarity activates MCs in the absence of mechanotransduction. Thus, mechanotransduction and osmoreception are likely distinct pathways.
authors.affiliation: University of Brest, European University of Brittany, Laboratory on Nervous Factors and Tissular Structure, EA4326, CHU, Brest, France.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Boulais
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Pennec
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lebonvallet
authors.forename: Ulysse
authors.initials: U
authors.lastname: Pereira
authors.forename: Nathalie
authors.initials: N
authors.lastname: Rougier
authors.forename: Germaine
authors.initials: G
authors.lastname: Dorange
authors.forename: Christophe
authors.initials: C
authors.lastname: Chesné
authors.forename: Laurent
authors.initials: L
authors.lastname: Misery
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology / Q000379:methods; D006632:Histamine / Q000378:metabolism; D008297:Male; D008465:Mechanoreceptors / Q000378:metabolism; D008564:Membrane Potentials; D018862:Merkel Cells / Q000166:cytology*; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009995:Osmosis; D011188:Potassium / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D006632:Histamine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium