title: Mechanism of extraneuronal adrenaline release induced by K+-free medium and ouabain, but not by high KCl in vas deferens of guinea-pig and rat.
abstract: The effects of K+-free medium, ouabain or high KCl on the contractile response and spontaneous efflux of adrenaline were analyzed in denervated guinea-pig or rat vasa deferentia preloaded with 3 x 10(-5) M (+/-)-adrenaline. The K+-free medium-induced contraction of guinea-pig tissues was related to the concentration of adrenaline used during preloading and was suppressed by the addition of 2.5 mM Rb+ but not by 2.5 mM Cs+. The contractile effects of K+-free medium and 10(-5) M ouabain, but not the response to high KCl, were prevented by 5 x 10(-6) M phentolamine or 3 x 10(-5) M deoxycorticosterone. These contractions, therefore, appear to be mediated by adrenaline released from the extraneuronal compartment. The K+-free medium- or ouabain-induced contractions of denervated rat vasa deferentia were small in comparison with those of the guinea-pig tissue. The amount of spontaneous efflux of adrenaline from the guinea-pig preparation was significantly enhanced by omission of K+ or by 10(-4) M ouabain but not by 80 mM KCl. K+-free medium and 3 x 10(-5) M ouabain merely elicited a small membrane depolarization accompanied by a slight decrease of membrane resistance in the guinea-pig vas deferens, whereas 30 mM KCl markedly altered these electrical parameters. From these findings, it is suggested that the rapid increase in extraneuronal amine release following inhibition of Na+-K+-ATPase may be due to some direct effect of K+ deficiency or of ouabain on the binding between the enzyme and the catecholamine rather than to alterations of membrane properties as a consequence of enzyme inhibition.
mesh_terms: D000818:Animals; D003714:Denervation; D004837:Epinephrine / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009474:Neurons / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology*; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D014649:Vas Deferens / Q000294:innervation / Q000378:metabolism*
chemical_list: D010042:Ouabain; D011189:Potassium Chloride; D000254:Sodium-Potassium-Exchanging ATPase; D004837:Epinephrine