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

Abstract

Summary . Guinea‐pig isolated trachea immersed in a low concentration (50 nm) of (—)‐3H‐noradrenaline accumulates radioactive material against an apparent concentration gradient. . 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. . Over a 25‐fold range of concentration the entry of either total radioactive material or noradrenaline followed Michaelis‐Menten kinetics. . The uptake of radioactive material was sodium‐dependent and ouabainsensitive. . 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. . 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.

Mechanism of efflux of noradrenaline from adrenergic nerves in rabbit atria

“…The amine accumulated under these conditions is, to a large extent, located in the cytoplasm Mechanism of noradrenaline eflux (Hamberger et al, 1964;Hamberger, 1967) although a small amount of reserpineresistant binding of noradrenaline occurs (Stitzel & Lundborg, 1967 Lindmar & Muscholl, 1971 ;Foster & O'Donnell, 1972;Starke, 1972). These workers reported that efflux could be resolved into two or three compartments.…”

Evidence That Adrenergic Nerves Are Responsible for the Active Uptake of Noradrenaline in the Guinea‐pig Isolated Trachea

“…None of the treatments shown in previous publications to inhibit significantly uptake-with-retention of radioactivity has abolished it; a residuum varying from approximately 1O pmol/g (ouabain, Foster & O'Donnell, 1972;and guanethidine, Foster, 1968) to 17 pmol/g (phenoxybenzamine, Foster, 1968) has always remained despite treatment with apparently maximally effective concentrations of inhibitors of uptake. O'Donnell & Saar (1973) have suggested, on the basis of histochemical evidence, that after incubation with a high concentration of noradrenaline the noradrenaline which is bound to cartilage (extraneuronal, extracellular) does not wash away quickly enough to be dissipated in 30 minutes.…”

“…The very fast exponential decay (t_ c 0.6 min) probably represents radioactive incubation medium adhering to the tissue on transfer to the first washing tube. The fast phase (tL c 6 min) represents radioactive material in the interstitial space of the tissue and the slow one (t_ c 120 min) 'cellular' radioactivity (Foster & O'Donnell, 1972).…”

“…Before freeze-drying the rings were incubated in a-methylnoradrenaline 1 ,M for 30 minutes. The remainder of the trachea was cut into rings and the uptake-with-retention of radioactive material measured according to the method of Foster & O'Donnell (1972) (Farmer & Coleman, 1970). A 20 min equilibration period at atmospheric pressure was allowed, plus a further 10 min after closing the system.…”

“…The trachea was then cut into rings and allowed to equilibrate in fresh Krebs solution containing atropine (350 nM) at 370 C for 1 h before transfer to 4 ml of incubation medium also containing (_)_[3 H] -noradrenaline (50 nM) and ascorbic acid (0.6 mM) for 15 minutes. The efflux of radioactive material on repeated washing of tissue was then measured, essentially by the method described by Foster & O'Donnell (1972) but following it for the longer time of 75 minutes.…”