抄録
A technique was devised for the separation of rat renal tubules in order to study the transport of 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT). The separated tubules maintained activities of aromatic amino acid decarboxylase and monoamine oxidase, and these activities were markedly depressed by Ro 4-4602 and pargyline, specific inhibitors for the respective enzymes. In the tubule cells incubated with 0.001 mM of the substrates, 30.4% of 14C-5-HTP was converted to 5-HT and 5-hydroxyindoleacetic acid (5-HIAA), and 69.0% of 14C-5-HT was converted to 5-HIAA. This metabolic conversion was almost completely inhibited by Ro 4-4602 and pargyline. The uptake of 14C-5-HTP or 14C-5-HT by the tubule cells under the presence of an enzyme inhibitor such as Ro 4-4602 and pargyline, proceeded linearly until 20 min at 37°C and the equilibrium distribution ratio for 14C-5-HTP and 14C-5-HT at the medium concentration of 0.001 mM was 3.4 and 14.9, respectively. The ratio for 14C-5-HT was markedly higher than that for 14C-5-HTP. The uptake did not occur at 0°C. Kinetic analysis of the rate of uptake at various concentrations of 14-5-HTP and 14C-5-HT indicated the presence of two saturable transport systems with defferent affinities for each substrate (Km: 0.08 mM and 7.0 mM for 5-HTP, 0.14 mM and 1.7 mM for 5-HT). It is concluded that renal tubule cells have temperature Dependent, concentrating and saturable transport systemx for 5-HTP and 5-HT.
