RESUMO
Trihydroxy bile acids with differing nonsterol chain length and charge were synthesized to define the effect of these parameters on the ability to competitively inhibit the Na(+)-dependent uptake of 14C taurocholate into isolated rat hepatocytes. Compounds with long side chains (greater than or equal to 0.8 nm) beyond carbon-17 of the sterol nucleus and carrying a negative charge or no charge were potent inhibitors. Introduction of a positive charge into the side chain weakened inhibition. When the length of the chain beyond carbon-17 fell below about 0.7 nm, charge still influenced inhibitory potency, but the effect was reversed and positively-charged chains yielded slightly greater inhibition than negatively-charged chains. From these results one may postulate a positively-charged cell surface domain extending outward from a point about 0.7 nm from the sterol nucleus receptor region. Up to about 0.7 nm from the sterol nucleus receptor region one might postulate a negative cell surface charge to account for the weaker inhibitory potency of compounds with short negatively-charged chains. Nonetheless, a short chain, regardless of charge, weakened inhibition, suggesting that a long negatively-charged side chain is necessary to orient the sterol moiety for optimal receptor fit. These data confirm that the Na(+)-dependent taurocholate transport site is sensitive to alterations of side chain charge and length and emphasize the importance of structure when designing bile acid analogs to probe taurocholate transport mechanisms.
