Weak base binding and transport in pig brush border membrane vesicles

AJ Moe, JA Hollywood and MJ Jackson

George Washington University Medical Center, Washington, District of Columbia.

Uptake of the weak bases, benzylamine and amphetamine, were characterized with pig intestinal brush border membrane vesicles. The absence of osmotic sensitivity indicated weak base binding and little or no transport into the brush border membrane vesicles at pH 7.4. Benzylamine binding was increased 30-fold when medium pH was increased from 7.0 to 9.0, which indicated binding of the nonionized form of benzylamine. Uptake of benzylamine into an osmotically sensitive space was observed at pH 9.0 in the presence of NaCl and no osmotic sensitivity was observed in the presence of KCl. The apparent energy of activation of benzylamine binding was 8.4 kCal/mol which is higher than values normally associated with a simple physical process such as diffusion or partition into the membrane. Benzylamine binding was saturable and two binding sites (KD = 25 microM, KD = 2.5 mM) were discriminated. Inhibition experiments with structurally related compounds indicated a high degree of structural selectivity for the binding sites. Analysis of inhibition patterns indicated that the amine nitrogen may act as a hydrogen acceptor for hydrogen bond formation. These results indicate binding of nonionized primary amines to specific sites on intestinal brush border membranes. The binding of primary amines may be important as a step in translocation and/or membrane discrimination between ionized and nonionized weak bases.

Volume 246, Issue 3, pp. 1012-1017, 09/01/1988
Copyright © 1988 by American Society for Pharmacology and Experimental Therapeutics