Participation of a transmembrane proton gradient in 5-hydroxytryptamine transport by platelet dense granules and dense-granule ghosts.
Dense granules, the storage organelles for 5-hydroxytryptamine in blood platelets, have been isolated from porcine platelets and are shown to transport 5-hydroxytryptamine in response to a transmembrane proton gradient (delta pH). Transport in the absence of delta pH is minimal, and it is shown that a rapid increase in transport takes place as delta pH increases. Direct measurements with [14C]methylamine show a delta pH of 1.1 units (acid inside) for intact granules. Osmotically active ghosts of dense granules from which 95% of the endogenous 5-hydroxytryptamine content has been released have also been prepared. Ghosts swell in the presence of ATP and Mg2+, and this swelling is shown to be due to the entry of protons via a process linked to ATP hydrolysis. Proton entry is also apparently linked to anion penetration in ghosts. Steady-state 5-hydroxytryptamine transport in ghosts is stimulated approx. 3-fold on the addition of ATP to the incubation medium, and the stimulation of 5-hydroxytryptamine transport in ghosts correlates with the formation of a transmembrane delta pH. Ghosts generate a delta pH of 1.1-1.3 pH units (acid inside) in the presence of 5 mM-ATP/2.5 mM-MgSO4. delta pH is generated within 3 min at 37 degrees C and is dissipated by the ionophore nigericin and by NH4Cl. It is shown that an Mg2+-stimulated ATPase activity is present on the ghost membrane, and inhibition of the ATPase leads to a corresponding decrease in 5-hydroxytryptamine transport. The results presented support the idea that 5-hydroxytryptamine transport into platelet dense granules is dependent on the presence of a transmembrane delta pH and, together with previous findings by others, suggest a generalized mechanism for biogenic amine transport into subcellular storage organelles.
D000251:Adenosine Triphosphatases / Q000097:blood; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000097:blood*; D013552:Swine
D012701:Serotonin; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases