The effect of various ions on uptake2 of catecholamines

1. The effects of a decrease of the K gradient on the extraneuronal inward transport and outward movement of catecholamines were studied in rat heart, rabbit aortic rings and guinea-pig trachealis smooth muscle. Elevation of the extracellular K concentration caused a) inhibition of the corticosteroid-sensitive extraneuronal uptake (uptake) ofH-isoprenaline in rat heart and ofH-noradrenaline in rabbit aorta, and b) acceleration of efflux ofH-isoprenaline from rat heart,H-noradrenaline from rabbit aorta and adrenaline (measured by microphotometry) from guinea-pig trachealis muscle. 2. In rat heart and rabbit aorta, the acute omission of one or the other of the ions Na, Cl, K or Ca from the perfusion or incubation medium had no effect on initial rates of uptake of catecholamines, except that the absence of K had a small inhibitory effect in the rat heart. 3. The prolonged absence of Na, Ca or K from the perfusion or incubation medium caused a marked inhibition of uptake of catecholamines. These inhibitory effects developed more quickly in rat heart than in rabbit aorta. 4. These results are compatible with the possibility that either the K gradient across the cell membrane or the resting membrane potential is the force driving uptake