title: [Ca2+]i rises via G protein during regulatory volume decrease in rabbit proximal tubule cells.
abstract: Although animal cells swell in hypotonic medium, their volume is subsequently regulated by a net loss of KCl via Ca2(+)-dependent channels. A rise in intracellular free calcium ([Ca2+]i) thus appears to be an initial event in the adaptation of external tonicity, although details of this mechanism are not known. To investigate cell volume regulation, we measured [Ca2+]i (by use of fura-2) and cell diameters in single cells of cultured renal proximal convoluted tubule. We found that a rapid rise in [Ca2+]i occurred after cells were exposed to hypotonic solution (250 mosM) from 95.8 +/- 3.8 to 468.2 +/- 24 nM (n = 16). The rise in [Ca2+]i was not observed in cells exposed to Ca2(+)-free medium, and exposure to isotonic high-K or low-Na medium did not elicit a rise in [Ca2+]i, suggesting that this rise was a result of Ca2+ influx and not via voltage-dependent Ca2+ influx or decrease of Ca2+ efflux via Na(+)-Ca2+ pump. Pretreatment of cells with pertussis toxin dose dependently blocked the rise in [Ca2+]i. The hypotonic solution enhanced accumulations of inositol tris- and tetra-phosphate after a 1-min exposure. Studies that measured cell diameters suggest that recovery of cell volume may include the rise in [Ca2+]i. These data suggest that the regulatory volume decrease of proximal tubule cells involves a pertussis toxin-sensitive guanine nucleotide binding protein-operated Ca2+ influx.
authors.affiliation: Second Department of Internal Medicine, Jikei University School of Medicine, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: K
authors.initials: K
authors.lastname: Kawahara
authors.forename: A
authors.initials: A
authors.lastname: Ogawa
authors.forename: T
authors.initials: T
authors.lastname: Morita
authors.forename: Y
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: S
authors.initials: S
authors.lastname: Kurihara
authors.forename: O
authors.initials: O
authors.lastname: Sakai
mesh_terms: D000818:Animals; D001572:Benzofurans; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism*; D003470:Culture Media; D016257:Fura-2; D019204:GTP-Binding Proteins / Q000502:physiology*; D007038:Hypotonic Solutions; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011817:Rabbits
chemical_list: D001572:Benzofurans; D003470:Culture Media; D007038:Hypotonic Solutions; D019204:GTP-Binding Proteins; D002118:Calcium; D016257:Fura-2