Transport of benzylpenicillin in gastrointestinal epithelia of the rat in vitro.

A steady-state net absorptive movement of benzylpenicillin across rat small intestine was observed in the absence of transmural gradients of electrochemical potential. The transport process was dependent on tissue metabolism and the presence of sodium, but no evidence of a saturable rate-limiting step was observed. Voltage-clamp studies showed that the transintestinal movement of benzylpenicillin varied with the electric potential across the tissue. It was found that a mathematical model based on a series three-compartment system yielded a good quantitative description of benzylpenicillin transport in the short-circuited condition and of the voltage-dependence of the transport process. A net absorptive movement of benzylpenicillin was also observed in studies on rat stomach in vitro, but on the colon a net secretory movement occurred. It was suggested that the gastric and colonic transport processes may be described in terms similar to those of the small intestine and that the variations of the direction of transport reflect differences in the pattern of acid-base metabolism in tissue.