MYOINOSITOL AND BETAINE TRANSPORTERS REGULATED BY TONICITY ARE BASOLATERAL IN MDCK CELLS
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- MYOINOSITOL AND BETAINE TRANSPORTERS REGULATED BY TONICITY ARE BASOLATERAL IN MDCK CELLS
- YAMAUCHI, A; Kwon, H. Moo; UCHIDA, S; PRESTON, AS; HANDLER, JS
- Issue Date
- American Physiological Society
- AMERICAN JOURNAL OF PHYSIOLOGY, v.261, no.1, pp.F197 - F202
- Myo-inositol and glycinebetaine are compatible osmolytes accumulated in the renal medulla and in MDCK cells cultured in hypertonic media. Both osmolytes are taken up by MDCK cells on Na-coupled transporters. The maximal velocity (V(max)) of both cotransporters is increased by culture in hypertonic medium. When hypertonic MDCK cells are shifted to isotonic medium there is a large transient efflux of osmolytes. To determine the polarity of the cotransporters and the transient efflux, we grew MDCK cells on a porous support to assay transport separately at their apical and basolateral surfaces. In hypertonic cells, basolateral uptake of both osmolytes was 1) more than 10-fold apical uptake, 2) > 96% Na dependent, 3) 25- (myo-inositol) and 16-fold (glycinebetaine) uptake in isotonic cells, reaching a maximum 24 h after the switch to hypertonic medium. When medium osmolarity was decreased from hypertonic to isotonic, myo-inositol uptake reversed to the isotonic level within 1 day; glycinebetaine uptake decreased more slowly. When medium osmolarity was decreased from hypertonic to isotonic, there was a large transient increase in basolateral efflux of both osmolytes.
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