AJP - Cell Physiology, Vol 252, Issue 5 C505-C514, Copyright © 1987 by American Physiological Society
Na microelectrode study of pathways of Na entry into Amphiuma intestinal absorptive cells
J. F. White, D. Ellingsen and S. Mayer
To define the pathways of Na+ entry into intestinal villus cells,
intracellular Na+ activity (aiNa) was measured in Amphiuma duodenum using
conventional and Na-sensitive microelectrodes. Replacement of Na+ in the
luminal medium reduced aiNa rapidly; replacement of Na+ in the serosal
medium caused a slow decline of aiNa. Hence, mucosal and serosal membranes
are both permeable to Na+. Ouabain addition to the serosal medium caused
aiNa to increase over 4 h. When Na+ was present only in the mucosal medium
and Na+ transport was inhibited with ouabain, aiNa increased over 4 h. With
galactose or valine (20 mM) in the mucosal medium aiNa was greater at 2 h
relative to paired control tissues. The gain in aiNa was unaffected by
replacement of luminal medium Cl- with gluconate or exposure to 1 mM
furosemide or amiloride. Amiloride, at 1 mM, was detected by the
Na-sensitive neutral carrier. Over a wide range of Na+ concentrations in
the luminal medium the rate of Na+ entry across the mucosal membrane
correlated strongly (r = 0.95) with the electrochemical gradient for Na+
across the luminal membrane. It is concluded that aiNa of urodele
intestinal cells is maintained at a low level by the operation of a Na+-K+
pump. Na+ entry across the luminal membrane occurs by diffusion and by the
cotransport with sugars and amino acids. Luminal NaCl cotransport and
Na+-H+ exchange do not appear to contribute to Na entry to a measurable
extent but it is possible that these transport processes operate at a slow
rate, but were inhibited secondary to inhibition of the Na-K pump.
