On the reduced retention of extravesicular noradrenaline in rabbit atria produced by potassium

The effects of KC1 on the retention of extravesicular (--)-[3H]noradrenaline were investigated. Atria, from reserpine-pretreated rabbits, were exposed to tropolone and pargyline before incubation with (--)-[3H]noradrenaline. After efflux for 50-60 min, exposure of tissues to media containing 65 mM KC1 resulted in increased efflux of (--)-[3H]noradrenaline. This effect was not Ca2+-dependent and was not altered by oxymetazoline, phentolamine, indomethacin or methacholine. The KC1-induced reduction in retention of (-)-[3H]noradrenaline was, however inhibited by cocaine and desipramine, but not by lidocaine. Efflux was not increased by RbCl and CsCl. It is suggested that KCl may have accelerated the efflux of extravesicular (--)-[3H]noradrenaline by increasing a cocaine- and desipramine-sensitive carrier-mediated efflux process.