Kinetics of taurocholate uptake by isolated ileal cells of guinea pig

Carrier-mediated uptake of taurocholate by ileal cells of guinea pig had an activation energy of 66 kJ/mol. There was no distinct pH optimum in the physiological pH range. Uptake was efficiently inhibited by cholate and taurochenodeoxycholate in a competitive manner, but less inhibited by bromosulfophthalein and not inhibited by taurine. The rate of uptake was related to the extracellular Na+ concentration up to 90 mM Na+. Stimulation by Na+ (up to sevenfold) occurred only in the presence of a transmembrane Na+ gradient, whereas high extracellular (Na+) in the absence of gradient did not stimulate. It is suggested that taurocholate is bound to a steroid-binding site of the carrier. The energy for the intracellular accumulation is largely provided by cotransport with Na+.