title: Physiological role of gap-junctional hemichannels. Extracellular calcium-dependent isosmotic volume regulation.
abstract: Hemichannels in the overlapping regions of apposing cells plasma membranes join to form gap junctions and provide an intercellular communication pathway. Hemichannels are also present in the nonjunctional regions of individual cells and their activity is gated by several agents, including calcium. However, their physiological roles are unknown. Using techniques of atomic force microscopy (AFM), fluorescent dye uptake assay, and laser confocal immunofluorescence imaging, we have examined the extracellular calcium-dependent modulation of cell volume. In response to a change in the extracellular physiological calcium concentration (1.8 to </=1.6 mM) in an otherwise isosmotic condition, real-time AFM imaging revealed a significant and reversible increase in the volume of cells expressing gap-junctional proteins (connexins). Volume change did not occur in cells that were not expressing connexins. However, after the transient or stable transfection of connexin43, volume change did occur. The volume increase was accompanied by cytochalasin D-sensitive higher cell stiffness, which helped maintain cell integrity. These cellular physical changes were prevented by gap-junctional blockers, oleamide and beta-glycyrrhetinic acid, or were reversed by returning extracellular calcium to the normal level. We conclude that nongap-junctional hemichannels regulate cell volume in response to the change in extracellular physiological calcium in an otherwise isosmotic situation.
authors.affiliation: Neuroscience Research Institute, University of California, Santa Barbara, CA 93106, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Quist
authors.forename: S K
authors.initials: SK
authors.lastname: Rhee
authors.forename: H
authors.initials: H
authors.lastname: Lin
authors.forename: R
authors.initials: R
authors.lastname: Lal
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002417:Cattle; D048429:Cell Size / Q000187:drug effects; D018031:Connexin 43 / Q000096:biosynthesis / Q000235:genetics; D017630:Connexins / Q000096:biosynthesis; D015638:Cytochalasin D / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004548:Elasticity; D004727:Endothelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D009829:Oleic Acids / Q000494:pharmacology; D009994:Osmolar Concentration; D051381:Rats; D014867:Water / Q000378:metabolism
chemical_list: D018031:Connexin 43; D017630:Connexins; D006993:Hypnotics and Sedatives; D007473:Ion Channels; D019384:Nucleic Acid Synthesis Inhibitors; D009829:Oleic Acids; D014867:Water; D015638:Cytochalasin D; C029407:oleylamide; D002118:Calcium