Myo-inositol and betaine transporters regulated by tonicity are basolateral in MDCK cells.
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 (Vmax) 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) greater than 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.
Yamauchi
A
A
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Kwon
H M
HM
Uchida
S
S
Preston
A S
AS
Handler
J S
JS
D000818:Animals; D001622:Betaine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001692:Biological Transport; D002460:Cell Line; D003470:Culture Media; D006982:Hypertonic Solutions / Q000494:pharmacology; D007294:Inositol / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007552:Isotonic Solutions; D007668:Kidney / Q000166:cytology / Q000378:metabolism*
D003470:Culture Media; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D001622:Betaine; D007294:Inositol