Extraneuronal inactivation of noradrenaline in tissue culture.

Corticosterone-sensitive extraneuronal transport (uptake2) and metabolism of noradrenaline was investigated in the clonal human Caki-1 cell line. Caki-1 cells are the first experimental system for uptake2 which is based on a tissue culture technique. Previous experiments with Caki-1 cells opened the possibility of a close relationship between uptake2 and the renal transport system for organic cations (RTOC). The finding that steroids potently inhibit both uptake2 and RTOC further supports this hypothesis. Noradrenaline which has been taken up into Caki-1 cells by uptake2 is metabolized by the intracellular enzymes catechol-O-methyltransferase (COMT) and to a lesser extend by monoamineoxidase (MAO).