Characterization of Na-H exchange in apical membrane vesicles of rat colon

Journal Article · Fri May 25 00:00:00 EDT 1990 · Journal of Biological Chemistry; (USA)

OSTI ID:6868744

Rajendran, V M; Binder, H J ^[1]

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1. Yale Univ., New Haven, CT (USA)

This study establishes the characteristics of electroneutral Na-H exchange present in apical membrane vesicles isolated from colonocytes of rat large intestine. An outward directed proton gradient stimulated 22Na uptake and demonstrated transient accumulation that was not altered by voltage clamping with K and its ionophore, valinomycin. Amiloride inhibited proton gradient-stimulated 22Na (0.1 mM) uptake by 97% by a noncompetitive mechanism with a Ki of 27 microM. 5-(N-ethyl-N-isopropyl)amiloride, an amiloride analogue which is a specific potent inhibitor of electroneutral Na-H exchange, inhibited proton gradient-stimulated 22Na uptake with a Ki of 400 nM. Increasing Na concentration saturated the proton gradient-stimulated 22Na uptake with an apparent Km of 11.7 +/- 2.2 mM. Increasing intravesicular proton concentration also resulted in saturation of 22Na uptake with a Km of 2.8 microM. Proton gradient-stimulated 22Na uptake was inhibited significantly by 10 mM Na+, Li+, and NH4+, while outward directed gradients of these ions in the absence of proton gradient accelerated 22Na uptake. The mechanism of Li+ inhibition of proton gradient-stimulated 22Na uptake was competitive with a Ki of 2 mM. 22Na uptake either stimulated by an outward directed Na gradient (i.e. Na-Na exchange) at pH 5.5, 6.5, and 7.5 or stimulated by 10-fold outward directed proton gradient at different pH values was similar; observations that do not suggest proton activation of Na-H exchange. We conclude from these results that proton gradient-stimulated 22Na uptake in colonic apical membrane vesicles represents tightly coupled electro-neutral Na-H exchange with several kinetic properties unlike those described in other epithelia.

• OSTI ID: 6868744
• Journal Information: Journal of Biological Chemistry; (USA), Journal Name: Journal of Biological Chemistry; (USA) Vol. 265:15; ISSN JBCHA; ISSN 0021-9258
• Country of Publication: United States
• Language: English

Related Subjects

551001* -- Physiological Systems-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL ISOTOPES
ALKALI METALS
ANIMALS
BARYONS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BODY
CATIONS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
CHEMICAL COMPOSITION
DIGESTIVE SYSTEM
ELEMENTARY PARTICLES
ELEMENTS
FERMIONS
GASTROINTESTINAL TRACT
HADRONS
INTESTINES
ION EXCHANGE
IONS
ISOMERIC TRANSITION ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LARGE INTESTINE
LIGHT NUCLEI
MAMMALS
MEMBRANE TRANSPORT
MEMBRANES
METALS
MUSCLES
NUCLEI
NUCLEONS
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PROTEINS
PROTONS
RADIOISOTOPES
RATS
RODENTS
SODIUM
SODIUM 22
SODIUM ISOTOPES
TRACER TECHNIQUES
VERTEBRATES
YEARS LIVING RADIOISOTOPES