Relationship Between the Systems Responsible for Uptake of 5-hydroxytryptamine and of Noradrenaline by Human Blood Platelets

Human blood platelets carry a high affinity, but low capacity, saturable system for the uptake of noradrenalhe. The uptake is partially Na(+) dependent but cannot be categorised as uptake. It is distinct from the uptake system responsible for 5-hydroxytryptamine transport into the platelet since the selective inhibitors of the platelet uptake system for 5-hydroxytryptamine (citalopram, paroxetine) Wer from those for the uptake system for noradrenaline (normetanephrine, methylisoprenaline). 5-hydroxytryptamine inhibits noradrenaline uptake but with properties inconsistent with competition for the same uptake system while noradrenaline does not inhibit 5-hydroxytryptamine uptake. Neither noradrenaline nor 5-hydroxytryptamine uptake by human platelets is inhibited by dopamine.