Sodium transport in human intestinal basolateral membrane vesicles.
The current investigation was aimed at characterizing transport pathways for Na+ in basolateral membrane vesicles (BLMV) isolated from organ donor jejunum and ileum. An outward proton gradient [pH inside, 5.5; pH outside, 7.5] led to a 4-5-fold stimulation of transport rates compared with the absence of proton-gradient conditions in both human jejunal and ileal BLMV. Voltage-clamping the vesicles (K+ inside = K+ outside + valinomycin) reduced the uptake of 22Na by 20%, indicating a minor conductive component of Na+ transport. Uptake of 22Na (1 mmol/L) in voltage-clamped BLMV was inhibited 70% by 2 mmol/L amiloride. Li+ and NH4+ inhibited transport of 22Na into voltage-clamped BLMV. Transport of Na+ exhibited saturation kinetics, and the Michaelis constant (Km) and Vmax values for jejunum and ileum were similar [Km, 27 +/- 3 mmol/L (jejunum) and 18 +/- 2 mmol/L (ileum); Vmax, 19 +/- 2 nmol.mg protein-1.min-1 (jejunum) and 16 +/- 1 nmol.mg protein-1.min-1 (ileum)]. Vmax values were < 15% of those reported for brush border membrane, whereas Km values were comparable. The results show that Na+ transport in human jejunal and ileal BLMV occurs via an Na+/H+ exchanger and a minor conductive pathway.
Zamir
Z
Z
Department of Medicine, Zablocki Veterans Administration Medical Center, Milwaukee, Wisconsin.
Barry
J A
JA
Ramaswamy
K
K
D000584:Amiloride / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000502:physiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000648:ultrastructure; D007583:Jejunum / Q000378:metabolism; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D001639:Bicarbonates; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D012964:Sodium