Dual mechanism of ouabain action on noradrenaline output from guinea-pig vas deferens.
Isolated guinea-pig vas deferens was used to test the effects of varying the concentration of extracellular Na+, Ca2+ and Mg2+ and the influence of tetanic transmural stimulation and of tetrodotoxin on the ouabain-induced increase in noradrenaline output. The total amount of noradrenaline released by ouabain increased with increasing concentration of either Na+ (from 35 to 143 mM) or Ca2+ (from 0.3 to 2.5 mM). The rise in the ouabain-induced increase of noradrenaline output was retarded by increasing the concentration of either Ca2+ from 0.3 to 5 mM or Mg2+ from 1.2 to 20 mM. Tetanic transmural stimulation facilitated the occurrence of ouabain-induced noradrenaline output, while tetrodotoxin (5 X 10(-7) g/ml) greatly inhibited it. These results suggest that ouabain causes an increase in noradrenaline output through at least two different mechanisms, a tetrodotoxin-sensitive action potential and Na+-dependent Ca2+ influx resulting from the inhibition of the Na+-K+ pump.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014649:Vas Deferens / Q000187:drug effects
D010643:Phenoxybenzamine; D013779:Tetrodotoxin; D010042:Ouabain; D012964:Sodium; D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine