INHIBITORY EFFECT OF OKADAIC ACID ON NORADRENALINE EXOCYTOSIS FROM GUINEA-PIG VAS-DEFERENS

The effects of okadaic acid (30 mu M), a protein phosphatase inhibitor , on noradrenaline (NA) release evoked by 70 mM KCl and 100 mu M ouaba in were evaluated in guinea-pig vas deferens. Release of NA evoked by high KCl was inhibited by okadaic acid but this inhibition was antagon ized by Bay K 8644. Furthermore, okadaic acid, like Ca2+-channel block ers, reduced NA release by ouabain. However, ATP release induced by ag -methylene ATP was virtually unaffected by okadaic acid or Ca2+-free m edium. These findings suggest that phosphatases may play an important role in Ca2+-channel activation and consequent NA exocytosis from adre nergic nerves.