Effect of Potassium on the Release of [3H]Noradrenaline from Rabbit and Human Pulmonary Artery

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Abstract
The release of [3H]noradrenaline [norepinephrine] ([3H]NA) from rabbit and human isolated pulmonary artery was measured. Removal of external K+ enhanced both the resting and stimulated release of [3H]NA from the strips. On adding K+ to tissues which were suspended in K+-free Krebs solution, the release of [3H]NA was reduced in both stimulated and unstimulated tissues. Selective inhibition of presynaptic .alpha.2-adrenoceptors by yohimbine significantly potentiated the release of [3H]NA evoked by stimulation in K+-free solution. The presynaptic inhibitory effect of NA was much less pronounced when the release was enhanced by the removal of external K+. Since the activity of Na, K-ATPase may be affected by removing K+ or by adding it to tissue previously kept in K+-free solution, the results may indicate involvement of the Na pump in NA release.