Some evidence of the active uptake of noradrenaline in the guinea-pig isolated trachea

Abstract

1 . Guinea-pig isolated trachea immersed in a low concentration (50 nm) of (—)-³H-noradrenaline accumulates radioactive material against an apparent concentration gradient. 2 . Compartmental analysis based on the decay curve of radioactive material content during washout and its comparison with that of ¹⁴C-sorbitol shows that some extracellular noradrenaline is adsorbed. A considerable mass exists in a slowly exchanging compartment, i.e. is retained. This retention is inversely concentration dependent. 3 . Over a 25-fold range of concentration the entry of either total radioactive material or noradrenaline followed Michaelis-Menten kinetics. 4 . The uptake of radioactive material was sodium-dependent and ouabainsensitive. 5 . The uptake was susceptible to metabolic poisons which deprive the tissue of all available energy but it was not exclusively associated with either oxidative or glycolytic energy supply. 6 . Although net uptake could not be distinguished from exchange with endogenous amine, other evidence has been obtained for an active noradrenaline transport system with properties similar to neuronal uptake.