title: Osmotic swelling activates two pathways for K+ efflux in a rat hepatoma cell line.
abstract: The pathways for the efflux of K(+) from osmotically-swollen HTC rat hepatoma cells were investigated using (86)Rb(+) as a tracer for K(+). Exposure of HTC cells to a hypotonic solution (<250 mOsm kg(-1)) resulted in a transient efflux of (86)Rb(+) that reached a maximal value after approximately 1 min, and inactivated within 3 min. This initial (86)Rb(+) efflux was inhibited by charybdotoxin, clotrimazole and Ba(2+), but not by apamin or paxilline, consistent with it being via an intermediate-conductance Ca(2+)-activated K(+) channel. For cells exposed to an extracellular osmolality < 180 mOsm kg(-1) there was an additional (86)Rb(+) efflux component which was slower to activate, taking 4 - 6 min to reach a maximum, and remaining active for > 20 min. The second (86)Rb(+) efflux component was not inhibited by K(+) channel blockers but was inhibited by the anion channel blockers, tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and niflumate. The time-courses for its activation and inactivation, as well as its dependence on the extracellular osmolality, were very similar to those observed for the hypotonically-activated efflux of the organic osmolyte, taurine. The data are consistent with the second component of (86)Rb(+) efflux and the efflux of taurine from osmotically-swollen cells occurring via a common pathway having a marked selectivity for taurine over (86)Rb(+).
authors.affiliation: School of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, ACT, Australia. pauline.junankar@anu.edu.au
authors.forename: Pauline R
authors.initials: PR
authors.lastname: Junankar
authors.forename: Ari
authors.initials: A
authors.lastname: Karjalainen
authors.forename: Kiaran
authors.initials: K
authors.lastname: Kirk
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D045744:Cell Line, Tumor; D008113:Liver Neoplasms / Q000378:metabolism*; D009994:Osmolar Concentration; D009995:Osmosis; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012414:Rubidium Radioisotopes; D013654:Taurine / Q000378:metabolism*
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D013654:Taurine; D011188:Potassium