Cell-matrix interactions modulate transepithelial phosphate transport in Pi-deprived OK cells

• Published in: American Journal of Physiology: Cell Physiology Vol. 293; no. 4; p. C1272
• Main Authors: Barac-Nieto, Mario, Weinman, Edward J, Spitzer, Adrian
• Format: Journal Article
• Language: English
• Published: 01.10.2007
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00051.2006

1 Department of Physiology, Faculty of Medicine, Kuwait University, Kuwait; 2 Department of Pediatrics, Albert Einstein College of Medicine, New York, New York; and 3 Department of Medicine, University of Maryland, Baltimore, Maryland Submitted 5 February 2006 ; accepted in final form 20 July 2007 In opossum kidney (OK) cells as well as in kidney proximal tubules, P i depletion increases apical (A) and basolateral (B) Na + -dependent P i cell influxes. In OK cells' monolayers in contrast to proximal tubules, there is no increase in transepithelial P i transport. This limitation may be due to altered cell-matrix interactions. A and B cell 32 P i uptakes and transepithelial 32 P i and [ 14 C]mannitol fluxes were measured in OK cells grown on uncoated or on Matrigel-coated filter inserts. Cells were exposed overnight to solution of either low (0.25 mM) or high (2.5 mM) P i . When grown on Matrigel, immunofluorescence of apical NaPi4 (an isoform of the sodium-phosphate cotransporter) transporters increased and A and B 32 P i uptakes into P i depleted cells were five and threefold higher than in P i replete cells ( P < 0.001). P i deprivation resulted in larger increase in A to B (4.6 x , P < 0.001) than in B to A (3.5 x , P < 0.001) P i flux and net P i transport from A to B increased 10-fold ( P < 0.001). With P i depletion increases in B to A (3.4 x ) and A to B (3.3 x ) paracellular [ 14 C]mannitol fluxes were similar, and its net flux was opposite to that of P i . In cells grown on uncoated filters, transepithelial and paracellular unidirectional and net P i fluxes decreased or did not change with P i depletion, despite twofold increases in apical and basolateral P i cell influxes. In summary, Matrigel-OK cell interactions, particularly in P i -depleted cells, led to enhanced expression of apical NaPi4 transporters resulting in higher P i transport rates across cell boundaries; apical P i readily entered the transcellular transport pool and paracellular fluxes were smaller fractions of transepithelial P i fluxes. These Matrigel-induced changes led to an increase in net transepithelial apical to basolateral P i transport. renal; mineral; transport; paracellular; transcellular; cell compartments Address for reprint requests and other correspondence: M. Barac-Nieto, Dept. of Physiology, Kuwait Univ., POB 24923, Safat 13110 Kuwait (e-mail: mario{at}hsc.edu.kw )