[3H]Xylamine accumulation by two sympathetically innervated tissues

The accumulation of [3H]xylamine [( ring-G-3H]-N-2'-chloroethyl-N-ethyl-2-methylbenzylamine; [3H]XYL) by rabbit thoracic aorta and rat vas deferens was studied in vitro. [3H]XYL uptake in both tissues saturated at the same concentrations and displayed the same time course as that for maximal inhibition of [3H]noradrenaline [( 3H]NA) accumulation by XYL. Hydrolysis of [3H]XYL or coincubation with Na2S2O3 reduced tissue accumulation of tritium by 80%. In aorta and vas deferens, about 45% and 65%, respectively, of the total [3H]XYL accumulation was blocked by 100 mumol/L desmethylimipramine (DMI), l-NA, or bretylium. In the absence of sodium ion, the uptake of [3H]XYL was reduced by approximately these same amounts. In both tissues nearly 70% of the [3H]XYL taken up was protein-bound when measured as trichloroacetic acid-precipitated tritium. Of this radioactivity, the same proportion was sensitive to 100 mumol/L DMI or the absence of sodium ion as found for total tissue accumulation of [3H]XYL. Hydrolysis of [3H]XYL prior to incubation with vas deferens reduced the protein-bound tritium by more than 95%. The studies indicate that [3H]XYL interacts with NA uptake carrier in both rabbit aorta and rat vas deferens and that a substantial portion of the resulting protein-bound radioactivity is carrier-dependent.