Abstract
We have investigated the volume-activated transport of organic solutes in flounder erythrocytes. Osmotic swelling of cells suspended in a Na(+)-free medium led to increased membrane transport of taurine, glucose, and uridine. For each compound there was a significant lag period (1-2 min at 10 degrees C) between cell swelling and activation of the flux. The volume-activated fluxes of each of the substrates increased in parallel with increasing cell volume, and those of taurine and uridine increased linearly with concentration (up to 19 mM). The volume-activated fluxes of each of the three compounds showed similar sensitivities to a number of anion-selective channel blockers (5-nitro-2-(3-phenylpropylamino)benzoic acid > 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid approximately MK-196 > niflumic acid > furosemide); the IC50 for the inhibition of the volume-activated fluxes by NPPB was around 12 microM. The results are consistent with the hypothesis that the volume-activated transport of organic osmolytes is via a pathway with the characteristics of a volume-activated "chloride channel." This raises the question of whether the transport of organic substrates might represent a physiological role for such channels in other cell types.
Highlights
In contrast to the situation wvitohlume-regulatory K’ and C1- transport, there is little known about the mechanisms
Osmotic The membrane transport of organic solutes is normally meswelling of cells suspended in a Na+-free medium led diated by “carriers” which are characterized by a high degree to increased membrane transport of taurine, glucose, of substrate selectivity, saturationkinetics,and,inmany and uridine
The results areconsistent with the hypothesis that the volume-activated transport of organic osmolytes is via a thatthepathways involved arequiteunlikeconventional amino acid or sugar transporters (Fincham et al, 1987; Siebens and Spring1, 989; Sanchez Olea et al, 1991;Jesus Garcia et al, 1991; Schousboe et al, 1991)
Summary
Vol 267, No 33, Issue of November 25, pp. 23475-23476,1992 0 1992 by The American Society for Biochemistry and Molecular Biology, Inc. 23475-23476,1992 0 1992 by The American Society for Biochemistry and Molecular Biology, Inc. Vol 267, No 33, Issue of November 25, pp. The volume-activated fluxes rine and sorbitol transport iannumber of different cell types of each of the substrates increased in parallel with increasing cell volume, and those of taurine and uridine increased linearly with concentration (up to 19 mM). The results areconsistent with the hypothesis that the volume-activated transport of organic osmolytes is via a thatthepathways involved arequiteunlikeconventional amino acid or sugar transporters (Fincham et al, 1987; Siebens and Spring 989; Sanchez Olea et al, 1991;Jesus Garcia et al, 1991; Schousboe et al, 1991). In the work reported here we have investigated the transport of representatives of three different classes of organic substrates in flounder erythrocytfeosllowing hypotonic swelling: taurine (an amino acid)g,lucose (a monosaccharide), and uridine(a nucleoside). Pathway with the characteristics of a volume-activated “chloridechannel.”This raises thqeuestion of whether
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