Inhibitory effect of okadaic acid on noradrenaline exocytosis from guinea-pig vas deferens.

The effects of okadaic acid (30 microM), a protein phosphatase inhibitor, on noradrenaline (NA) release evoked by 70 mM KCl and 100 microM ouabain were evaluated in guinea-pig vas deferens. Release of NA evoked by high KCl was inhibited by okadaic acid but this inhibition was antagonized by Bay K 8644. Furthermore, okadaic acid, like Ca(2+)-channel blockers, reduced NA release by ouabain. However, ATP-release induced by alpha,beta-methylene ATP was virtually unaffected by okadaic acid or Ca(2+)-free medium. These findings suggest that phosphatases may play an important role in Ca(2+)-channel activation and consequent NA exocytosis from adrenergic nerves.