title: Intracellular calcium changes trigger connexin 32 hemichannel opening.
abstract: Connexin hemichannels have been proposed as a diffusion pathway for the release of extracellular messengers like ATP and others, based on connexin expression models and inhibition by gap junction blockers. Hemichannels are opened by various experimental stimuli, but the physiological intracellular triggers are currently not known. We investigated the hypothesis that an increase of cytoplasmic calcium concentration ([Ca2+]i) triggers hemichannel opening, making use of peptides that are identical to a short amino-acid sequence on the connexin subunit to specifically block hemichannels, but not gap junction channels. Our work performed on connexin 32 (Cx32)-expressing cells showed that an increase in [Ca2+]i triggers ATP release and dye uptake that is dependent on Cx32 expression, blocked by Cx32 (but not Cx43) mimetic peptides and a calmodulin antagonist, and critically dependent on [Ca2+]i elevation within a window situated around 500 nM. Our results indicate that [Ca2+]i elevation triggers hemichannel opening, and suggest that these channels are under physiological control.
authors.affiliation: Department of Physiology and Pathophysiology, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium.
authors.forename: Elke
authors.initials: E
authors.lastname: De Vuyst
authors.forename: Elke
authors.initials: E
authors.lastname: Decrock
authors.forename: Liesbet
authors.initials: L
authors.lastname: Cabooter
authors.forename: George R
authors.initials: GR
authors.lastname: Dubyak
authors.forename: Christian C
authors.initials: CC
authors.lastname: Naus
authors.forename: W Howard
authors.initials: WH
authors.lastname: Evans
authors.forename: Luc
authors.initials: L
authors.lastname: Leybaert
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002413:Cations, Divalent / Q000032:analysis / Q000378:metabolism; D002478:Cells, Cultured; D017630:Connexins / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000378:metabolism; D058486:Receptors, Purinergic P2X7; D022161:Transport Vesicles / Q000187:drug effects / Q000378:metabolism; D000097002:Gap Junction beta-1 Protein
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium; D002147:Calmodulin; D002413:Cations, Divalent; D017630:Connexins; D010455:Peptides; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D000097002:Gap Junction beta-1 Protein; C546468:P2RX7 protein, human