Discrimination of monoamine uptake by membranes of adrenal chromaffin granules.
1 The accumulation of various radioactive monoamines by isolated membranes of bovine adrenal chromaffin granules was measured by equilibrium dialysis. 2 Adenosine-5'-triphosphate (ATP) in the presence of Mg++ stimulated the uptake of all the amines tested, but the accumulation of dopamine, (-)-noradrenaline (NA), 5-hydroxytryptamine (5-HT), (plus or minus)-adrenaline and (plus or minus)-octopamine was greater than that of tyramine, (plus or minus)-metaraminol, tryptamine, beta-phenylethylamine and histamine. 3 At the higher concentration levels of the amines in the medium the ATP-dependent accumulation of dopamine, NA, adrenaline and 5-HT in the membranes reached a saturation level, whereas in the absence of the nucleotide no saturation level was attained. 4 Octopamine and 5-HT competitively inhibited the ATP-dependent uptake of NA, 5 Decrease in the incubation temperature or the presence of N-ethylameimide greatly reduced the ATP-stimulated amine accumulation. Ouabain had no effect on uptake. 6 Reserpine virtually abolished the ATP-dependent uptake of dopamine, NA and 5-HT, caused a partial inhibition of the metaraminol, octopamine and tyramine accumulation, but did not interfere with the uptake of tryptamine. 7 The content of endogenous catecholamines of the membranes was changed very little by incubation of NA and 5-HT in the presence of ATP. However, the membranes lost over 80% of their endogenous amines if incubated for 30 min without ATP. 8 The ATP content of the medium progressively decreased during the incubation of granular membranes. 9 It is concluded that the membrane of adrenal chromaffin granules discriminates between the various monoamines with regard to the magnitude of their uptake and that two mechanisms of ATP-stimulated uptake, one responsive and the other resistant to reserpine, exist at the level of this membrane. The ATP-stimulated transport at the granular membrane level may be an important factor in determining the intraneuronal storage of a physiological or false neurotransmitter.
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000311:Adrenal Glands / Q000378:metabolism*; D000588:Amines / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002838:Chromaffin System / Q000648:ultrastructure*; D003594:Cytoplasmic Granules / Q000378:metabolism*; D066298:In Vitro Techniques; D008566:Membranes / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D013268:Stimulation, Chemical; D013997:Time Factors
D000588:Amines; D002395:Catecholamines; D000255:Adenosine Triphosphate; D009638:Norepinephrine