AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 4 704-R711, Copyright © 1991 by American Physiological Society
Effects of pH on phosphate transport by flounder renal tubule primary cultures
A. Gupta and J. L. Renfro
Department of Physiology and Neurobiology, University of Connecticut, Storrs 06269.
Transepithelial phosphate (Pi) fluxes were determined in primary monolayer
cultures of the winter flounder proximal tubule in Ussing chambers. Net Pi
secretion, peritubular (P)-to-lumen (L) net flux (Jnet = 17.0 +/- 3.77
nmol.cm-2.h-1), was strongly stimulated by lowering peritubular pH to 6.5
(pHP 6.5 vs. pHL 7.5) compared with control tissues at pH 7.5 (pHP 7.5 vs.
pHL 7.5) where net reabsorption (L-to-P Jnet = 1.10 +/- 0.36 nmol.cm-2.h-1)
occurred. The stimulation of net secretion by pHP 6.5 was inhibited to 27%
of control by 200 microM amiloride. The imposition of a reversed pH
gradient (pHL 6.5 vs. pHP 7.5) did not stimulate Pi secretion.
Preincubation with 0.5 U/ml phospholipase C caused a nearly fivefold
stimulation of Pi secretion compared with the untreated controls. H-7 (100
microM), a protein kinase inhibitor, caused a 2.5-fold reduction in phorbol
ester (PE)-induced stimulation of Pi secretion. H-7 also significantly
inhibited Pi secretion (50% reduction) when peritubular pH was lowered to
6.5. PE-induced net Pi secretion was significantly lower when luminal pH
was lowered to 5.5 compared with controls where luminal pH was kept at 7.5.
Amiloride (200 microM) significantly inhibited the PE-induced net Pi
secretion in the presence of luminal pH 7.5 but had no significant effect
at luminal pH 5.5. Replacement of luminal NaCl with LiCl or isosmolar
mannitol significantly reduced net phosphate secretion under the conditions
of lowered peritubular pH. Net Pi secretion was also dependent on the
maintenance of a cellular Na+ gradient, since 100 microM ouabain inhibited
PE-induced net Pi secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
