Bile-salt inhibition of sodium ion-coupled D-glucose and L-alanine accumulation by brush-border-membrane vesicles from hamster jejunum

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Abstract
The effects of bile salts on Na+-coupled accumulation of D-glucose and L-alanine by brush-border-membrane vesicles isolated from hamster jejunum were investigated. The approximate percentage inhibition of Na+-coupled D-glucose accumulation produced by various bile salts at a concentration of 1 mM were: deoxycholate and chenodeoxycholate, 60%; glycine and taurine conjugates of deoxycholate and chenodeoxycholate, 40-50%; lithocholate, 45% and cholate and its glycine and taurine conjugates, < 10%. Inhibition of Na+-coupled accumulation of D-glucose was rapid, reversible and not due to dissolution of the vesicles. Na+-coupled accumulation of L-alanine was also inhibited by deoxycholate. Deoxycholate but not cholate enhanced the rate of Na+ influx, the rate of influx of D-glucose and L-alanine in the absence of a Na+ gradient and the rate of efflux of D-glucose and L-alanine from vesicles preloaded with this sugar or amino acid. Deoxycholate-stimulated efflux of D-glucose was not blocked by phlorizin, which completely prevented efflux in the absence of this bile salt. Selected bile salts probably inhibit Na+-coupled accumulation of D-glucose and L-alanine by enhancing the rate of dissipation of the Na+ gradient required for substrate accumulation. Bile salts may also decrease D-glucose and L-alanine accumulation by increasing the rate of efflux of these substrates across the brush-border plasma membrane.