TY - JOUR T1 - Compartmental Analysis of Amine Storage in Bovine Adrenal Medullary Granules JF - Molecular Pharmacology JO - Mol Pharmacol SP - 308 LP - 316 VL - 7 IS - 3 AU - THEODORE A. SLOTKIN AU - ROBERT M. FERRIS AU - NORMAN KIRSHNER Y1 - 1971/05/01 UR - http://molpharm.aspetjournals.org/content/7/3/308.abstract N2 - The efflux of 14C-epinephrine from isolated bovine adrenal medullary granules was determined in order to study the storage and distribution of newly incorporated amines. After the granules had been labeled, the efflux of endogenous and 14C-epinephrine was measured for 1 hr at 37°. The efflux of 14C-epinephrine was biphasic: a period of fast efflux (25% of the 14C-epinephrine, t1/2 = 5 min) was followed by a period of slow efflux (75%, t1/2 = 2-3 hr). There appeared to be no exchange of 14C-epinephrine between the two efflux pools, suggesting that these might represent two populations of granules. By appropriate treatment, each pool could be preferentially loaded with 14C-epinephrine without altering its t1/2. The presence of reserpine (50 µM) or N-ethylmaleimide (150 µM), during loading, the absence of ATP and MgCl2, and the use of higher epinephrine concentrations or shorter incubation times all increased the percentage of catecholamine in the rapidly releasing pool and decreased its proportion in the slowly releasing pool. The net uptake of epinephrine was reduced in both pools when ATP-Mg2+-stimulated amine uptake was blocked. These observations suggest that epinephrine is taken up into two pools, one having a slower release rate than the other, a greater dependence on ATP-Mg2+-stimulated uptake, and a greater storage capacity. The effluxes of 3H-octopamine and 3H-metaraminol were biphasic, but differed from 14C-epinephrine in distribution and in the half-life of the slow phase: 32% of the 3H-octopamine was released with t1/2 = 5 min, and 68% with t1/2 = 50 min; 64% of the 3H-metaraminol was released with t1/2 = 6 min, and 36% with t1/2 = 37 min. ER -