Expression of Madin-Darby canine kidney cell Na(+)-and Cl(-)-dependent taurine transporter in Xenopus laevis oocytes.
Expression of a Madin-Darby canine kidney (MDCK) cell taurine transporter was examined in Xenopus oocytes that had been injected with poly(A)+ RNA extracted from MDCK cells. Compared with water-injected oocytes, injection of total poly(A)+ RNA resulted in an increase in Na(+)-dependent taurine uptake which was directly related to the amount of RNA injected. The magnitude of expression in poly(A)+ RNA-injected oocytes was 5-10-fold higher than that of water-injected oocytes. Since the Vmax of taurine uptake in MDCK cells is increased by culture in hypertonic medium, we compared oocyte taurine uptake after injection with poly(A)+ RNA from MDCK cells cultured in hypertonic medium with uptake in oocytes injected with poly(A)+ RNA from hypertonic cells elicited twice the taurine uptake elicited by poly(A)+ RNA from isotonic cells. The transporter expressed in oocytes was like that in MDCK cells: it was completely dependent on external sodium and was also anion dependent (Cl- greater than or equal to Br- greater than SCN- much greater than gluconate-). Other beta-amino acids, beta-alanine and hypotaurine, inhibited taurine uptake, but L-alanine and 2-(methylamino) isobutyric acid did not. The apparent Km of the transporter was 7.0 microM. After size fractionation on a sucrose density gradient, poly(A)+ RNA encoding for the MDCK taurine transporter was found in the fraction whose average size was 4.4 kilobases.
Uchida
S
S
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Kwon
H M
HM
Preston
A S
AS
Handler
J S
JS
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism; D011061:Poly A / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013379:Substrate Specificity; D013654:Taurine / Q000378:metabolism*; D014982:Xenopus laevis
D002352:Carrier Proteins; D002712:Chlorides; D013654:Taurine; D011061:Poly A; D012313:RNA; D012964:Sodium