Expression of proximal tubular na/phosphate and na/sulfate cotransport systems in mdck and llc-pk1 cells by transfection. Quabius, E. S., H. Murer, and J. Biber. Institute of Physiology, University of Z[umlaut]urich, CH-8057 Z[umlaut]urich
APStracts 2:0141F, 1995.
Two cDNA's coding for proximal tubular Na/Pi-cotransport (NaPi-2) and Na/SO4-cotransport (NaSi-1) have been transfected by the use of a dexamethasone inducible vector (pLK-neo) into MDCK and LLC-PK1 cells. By RT-PCR expression of corresponding mRNA's was observed after stimulation with dexamethasone only. Similarly, expression of the NaPi-2 protein was detected only after induction with dexamethasone. In transfected MCDK cells dexamethasone induced a large increase of Na/Pi- or Na/SO4-cotransport whereas in transfected LLC-PK1 cells transport was only minimally expressed. In MDCK cells grown on filter supports transfected Na/Pi-cotransport activity was equally expressed at both cell surfaces; dual location of expressed NaPi-2 protein was also observed by immunohistochemistry. In contrast, transfected Na/SO4-cotransport activity was predominantly expressed at the apical cell surface of MDCK cells. The results demonstrate i) that in MDCK cells the sorting behaviour of two proximal tubular cotransport systems seems to be different; apical for Na/SO4-cotransport (NaSi-1) and dual location for Na/Pi-cotransport (NaPi-2) and ii) that LLC-PK1 cells seem not to be a suitable system to functionally express sodium-dependent cotransport systems for phosphate and sulfate. 

Received 5 May 1995; accepted in final form 7 August 1995.
APS Manuscript Number F149-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.