Chloride-dependent intestinal transport of imino and β-amino acids in the guinea pig and rat

The present study extends the observations of chloride-dependent intestinal amino acid carriers to the guinea pig and the rat using the technique of in vitro influx across the brush-border membrane of intact epithelium. Transport rates of D-glucose and L-amino acids are lowest in guinea pig proximal small intestine and are constant from midjejunum through distal ileum, except for leucine. The guinea pig possesses a sodium- and chloride-dependent, high-affinity, very low-capacity carrier of β-amino acids for which taurine and β-alanine compete and for which the Na⁺- taurine activation stoichiometry is 2.1 ± 0.3:1. The imino acid carrier of the guinea pig is also chloride dependent with a Na⁺-Cl^--2-methylamino- isobutyric acid activation stoichiometry of 1.8 ± 0.1:0.7 ± 0.3:1. In contrast, the rat imino acid carrier is chloride independent and transport rates vary insignificantly along the small intestine. The rat taurine carrier has its maximal transport rate in midjejunum. It is chloride dependent but does not transport β-alanine.