Transport of 5-hydroxytryptamine by dense granules from porcine platelets.
A method is described for the isolation of a homogeneous preparation of dense granules from procine platelets. The purified dense granule fraction contained approximately 400 nmol of 5-hydroxytryptamine/mg of protein and appeared to be homogeneous when examined by electron microscopy. Isolated dense granules transport exogenously added 5-hydroxytryptamine via two mechanisms: 1) a carrier-mediated process predominating at low substrate concentrations and 2) a diffusion-controlled process predominating at high substrate concentrations. Temperature studies revealed an apparent energy of activation of 14.9 kcal/mol for the carrier-mediated transport. Kinetic data yielded a Km of 3.3 micron and a Vmax of 0.79 nmol/min/mg of protein for the mediated transport process. Steady state uptake was sensitive to changes in medium osmotic pressure and a decline in uptake below 300 mosM was correlated with release of endogenous 5-hydroxytryptamine. The transport was inhibited by a number of structural analogs of 5-hydroxytryptamine. These results demonstrate the existence of a carrier-mediated transport system for 5-hydroxytryptamine in the membranes of the platelet dense granules.
D000818:Animals; D001679:Biogenic Amines / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D001792:Blood Platelets / Q000378:metabolism*; D002458:Cell Fractionation / Q000379:methods; D002499:Centrifugation, Density Gradient; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D009997:Osmotic Pressure; D012701:Serotonin / Q000097:blood*; D013552:Swine; D013816:Thermodynamics
D001679:Biogenic Amines; D012701:Serotonin