Amine uptake into intact mast cell granules in vitro.
Histamine, the principal amine of rat peritoneal mast cells, is taken up into isolated granules with intact membranes. Uptake is pH- and concentration-dependent and is not stimulated by the addition of Mg2+-ATP. The saturable uptake has a Km of 91.1 microM and a Vmax of 95.4 pmol (mg of protein)-1 min-1. Uptake is abolished by 5 mM ammonium ion. 5-HT, the other endogenous amine of the granules, and dopamine and tyramine, which do not occur naturally in rat mast cells, each competitively inhibits [3H]-histamine uptake with Ki's close to 1 microM. Reserpine, a putative amine carrier blocker, inhibits uptake at nanomolar concentrations. At high concentrations, uptake of [3H]-5-HT is nonsaturable; at low concentrations, a saturable component is observed with a Km of 1.6 microM. Uptake of [3H]-5-HT is not enhanced by Mg2+-ATP. It is pH-dependent but with a lower apparent pKa than that of histamine. [3H]-5-HT uptake can be completely inhibited by ammonium ions. Amine inhibition of [3H]-5-HT gives nonlinear Dixon plots, and high concentrations of the competing amines or reserpine cannot completely block uptake. We propose a model consistent with these results in which amine uptake occurs by several distinct saturable transport systems. According to the model, histamine is transported by a single system, which also transports 5-HT and dopamine. 5-HT and dopamine are transported by one or more other systems.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000588:Amines / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport / Q000187:drug effects; D003594:Cytoplasmic Granules / Q000378:metabolism*; D006632:Histamine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008407:Mast Cells / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
D000588:Amines; D006632:Histamine; D000255:Adenosine Triphosphate