AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 2 264-R269, Copyright © 1987 by American Physiological Society
Tyrosine transport in winter flounder intestine: interaction with Na+-K+-2Cl- cotransport
M. W. Musch, F. M. McConnell, L. Goldstein and M. Field
Tyrosine absorption across the brush border of the intestinal epithelium of
the winter flounder Pseudopleuronectes americanus was studied in Ussing
chambers modified to determine early rates of uptake. At 0.1 mM tyrosine,
the 4-min rate of uptake (influx) of tyrosine across the brush border
averaged 37.5 nmol X cm-2 X h-1. Omission of Na decreased influx by 60%,
indicating that tyrosine influx occurs, at least in part, by a Na-coupled
process. Ouabain inhibited influx by 80%. Inhibition of brush border
Na+-K+-2Cl- cotransport by bumetanide, 8-bromo-cyclic GMP, or Cl
replacement stimulated tyrosine influx 2.5- to 4-fold. However, atriopeptin
III, which also inhibits Na+-K+-2Cl- cotransport, did not stimulate
tyrosine influx. Cyclic AMP, which does not appear to inhibit ion
cotransport, did not stimulate tyrosine influx. Both cyclic GMP and
bumetanide also stimulated the net mucosa-to-serosa tyrosine flux (43 and
29%, respectively) and increased the cellular concentration of tyrosine by
50%. Thus tyrosine's influx is increased to a greater extent than is its
transmural flux or its cellular concentration, suggesting that the main
change occurs at the brush border and represents large increases in both
influx and efflux of tyrosine across this membrane.
