title: Self-inhibition of chloride transport in Ehrlich ascites tumor cells.
abstract: Previous studies have shown that mediated Cl- transport which occurs by at least two processes (Cl- -dependent cation cotransport and Cl- self-exchange) becomes progressively inhibited when extracellular Cl- exceeds about 60 mM (Hoffmann et al., 1979). To account for this type of kinetic behavior, that is, self-inhibition, an anion transport system possessing two sites, a high affinity transport site and a lower affinity modifier site is suggested (Dalmark, 1976). In the present experiments we have attempted to determine which of the mediated transport pathways is susceptible to self-inhibition by studying the dependence of the steady state Cl- flux on the extracellular Cl- concentration and how DIDS, an inhibitor of Cl- self-exchange, and H + affect this relationship. Addition of DIDS to Ehrlich cells results in inhibition of Cl- transport at every Cl- concentration tested (40-150 mM). Moreover, the Cl- flux/Cl- concentration relationship no longer exhibits self-inhibition, suggesting that this phenomenon is a characteristic of the Cl- self-exchanger rather than of the Cl- -dependent cation cotransport system. Lowering the extracellular pH (pHo) from 7.35 to 5.30 stimulates Cl- transport by a process that saturates with respect to [H +]. Half-maximal stimulation occurs at pHo 6.34. A comparison of the kinetic parameters, Ks and Jmax, calculated from the ascending limb of the Cl- flux/Cl- concentration curve at pHo 7.30 to those at pHo 5.50 show that the values for Ks are almost identical (23.6 mM and 21.3 mM, respectively), while the values for Jmax [22.2 mEq/Kg dry wt) X min] differ by only 15%. This finding along with the observation that DIDS completely blocks H + stimulation of Cl- transport is compatible with the suggestion that H + interact at the modifer site of the Cl- self-exchanger and thereby prevents self-inhibition.
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D003470:Culture Media; D005246:Feedback; D005942:Gluconates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice
chemical_list: D002712:Chlorides; D003470:Culture Media; D005942:Gluconates; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid