Taurine transport by rat hepatocytes in primary culture

Hepatic taurine concentration is 30--100 times that of plasma, suggesting an efficient taurine uptake mechanism in the hepatocyte. The characteristics of hepatic taurine transport were studied in primary cultures of adult rat hepatocytes. Taurine uptake was concentrative and linear for over 4 h. At taurine concentrations 2.5--100 microM, uptake was saturable with constants Km = 44 microM, V = 0.28 nmol/mg protein per min and EA = 13.2 kcal/mol. Uptake was inhibited 41% by incubation under N2 and was competitively inhibited by beta-alanine (Ki = 94 microM) and hypotaurine (Ki = 14 microM). Uptake was linearly dependent upon Na+ concentration from 0 to 140 mM. A second nonsaturable uptake process was identifiable only at taurine concentrations greater than 1 mM. This process was presumed to represent passive diffusion. At taurine concentrations existing in plasma, taurine enters the hepatocyte primarily by a single, Na+-dependent, carrier-mediated, oxygen-requiring transport process.