title: Ca2+-mediated potentiation of the swelling-induced taurine efflux from HeLa cells: on the role of calmodulin and novel protein kinase C isoforms.
abstract: The present work sets out to investigate how Ca(2+) regulates the volume-sensitive taurine-release pathway in HeLa cells. Addition of Ca(2+)-mobilizing agonists at the time of exposure to hypotonic NaCl medium augments the swelling-induced taurine release and subsequently accelerates the inactivation of the release pathway. The accelerated inactivation is not observed in hypotonic Ca(2+)-free or high-K(+) media. Addition of Ca(2+)-mobilizing agonists also accelerates the regulatory volume decrease, which probably reflects activation of Ca(2+)-activated K(+) channels. The taurine release from control cells and cells exposed to Ca(2+) agonists is equally affected by changes in cell volume, application of DIDS and arachidonic acid, indicating that the volume-sensitive taurine leak pathway mediates the Ca(2+)-augmented taurine release. Exposure to Ca(2+)-mobilizing agonists prior to a hypotonic challenge also augments a subsequent swelling-induced taurine release even though the intracellular Ca(2+)-concentration has returned to the unstimulated level. The Ca(2+)-induced augmentation of the swelling-induced taurine release is abolished by inhibition of calmodulin, but unaffected by inhibition of calmodulin-dependent kinase II, myosin light chain kinase and calcineurin. The effect of Ca(2+)-mobilizing agonists is mimicked by protein kinase C (PKC) activation and abolished in the presence of the PKC inhibitor Gö6850 and following downregulation of phorbol ester-sensitive PKC isoforms. It is suggested that Ca(2+) regulates the volume-sensitive taurine-release pathway through activation of calmodulin and PKC isoforms belonging to the novel subclass (nPKC).
authors.affiliation: Biochemical Department, August Krogh Institute, Universitetsparken 13, Copenhagen, DK-2100 Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Falktoft
authors.forename: I H
authors.initials: IH
authors.lastname: Lambert
mesh_terms: D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism*; D048429:Cell Size; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007038:Hypotonic Solutions; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008301:Maleimides / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D004791:Enzyme Inhibitors; D007038:Hypotonic Solutions; D007211:Indoles; D007527:Isoenzymes; D008301:Maleimides; D013654:Taurine; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D002118:Calcium