Release, reuptake and net uptake of dopamine, noradrenaline and adrenaline in isolated sheep adrenal medullary granules.

Isolated storage granules from sheep adrenal medullary cells incubated in isotonic K-phosphate at 37° C give off dopamine (DA) and adrenaline (A) at characteristically different rates following an exponential course. The average half time for the DA release in granules during the prevailing conditions was 22 min and for A 49 min. Noradrenaline (NA) was released more rapidly during the initial stage and thereafter exponentially at a slow rate. DA in concentrations of 3 × 10-5 M in the incubation fluid increased the half time for DA to 34 min, owing to reuptake, and decreased it for A to 43 min. Addition of ATP-Mg, 3 mM, considerably decreased the release rate of DA as well as that of NA and A, presumably owing to inhibition of release and increased reuptake. In the presence of ATP-Mg the addition of 3 × 10-5 M DA further retarded the net release of DA from the storage granules. After partial depletion, the granules take up DA in the presence of ATP-Mg. This effect is inhibited by reserpine. No net uptake of NA or A was observed in partially depleted granules in the presence of added ATP-Mg. Addition of ATP-Mg retards the release of soluble proteins concomitantly with catecholamines. The rapidly released NA has been localized in the heavy granule fractions.