The acceleration of the extraneuronal efflux of 3H-(+/-)-isoprenaline induced by high extracellular potassium.

After loading of the extraneuronal tissues of the perfused rat heart with 3H-isoprenaline the elevation of extracellular K+ concentration (from 2.7 to 15 mmol/l) in the perfusion solution about doubled the rate constant for efflux of the 3H-amine. As this increase was not seen in the presence of 100 mumol/l 3-O-methyl-isoprenaline (OMI, a potent inhibitor of the uptake2-carrier), it is concluded that the change in the concentration of K+ modulates OMI-sensitive outward transport of 3H-isoprenaline by uptake2, not the diffusional efflux of the amine.