Characteristics of taurine transport in freshly isolated rat hepatocytes

Characteristics of taurine (2-aminoethanesulfonic acid) transport were studied in freshly isolated rat hepatocytes prepared by a collagenase perfusion technique. The uptake of taurine at 37 degrees C was linear up to 30 min of incubation, but gradually decreased thereafter and reached a plateau at 90 min after initiation of the incubation. Taurine uptake at 4 degrees C by isolated hepatocytes was not saturable, whereas that at 37 degrees C was saturable with the following parameters: Km, 37 microM; Vmax, 0.043 nmoles/mg prot./min; and EA, 5.6 Kcal/mol. The taurine uptake at 37 degrees C was found to be sodium dependent, and this was inhibited competitively by guanidinoethyl sulfonate and beta-alanine with the Ki values of 1.75 mM and 285 microM, respectively. Conjugated cholate, conjugated chenodeoxycholate, alanine, isethionate and leucine had no effect on the taurine uptake. The present results indicate that taurine uptake by isolated hepatocytes consists of unsaturable and energy independent, and carrier-mediated and energy dependent transport processes.