Isolated 5‐hydroxytryptamine organelles of rabbit blood platelets: physiological properties and drug‐induced changes

Abstract

1 . In isolated 5-hydroxytryptamine (5-HT) organelles of rabbit platelets, the concentrations of 5-HT, histamine and adenosinetriphosphate (ATP) respectively are about 200 times higher than in intact platelets. Organelles incubated in plasma at 37° C gradually lose endogenous 5-HT, histamine and ATP and take up ¹⁴C-5-HT against a considerable concentration gradient. Liberation and uptake of 5-HT markedly decrease with dimishing incubation temperature. 2 . Exposure to reserpine in vitro strongly counteracts the uptake of ¹⁴C-5-HT by isolated organelles, whereas the ¹⁴C-5-HT uptake of intact isolated platelets is less affected by the drug. 5-HT organelles of platelets from reserpinized rabbits also take up very little ¹⁴C-5-HT. 3 . Imipramine inhibits the uptake of ¹⁴C-5-HT in isolated organelles less markedly than in isolated platelets. 4 . It is concluded that in the organelles 5-HT and possibly histamine may be associated with ATP. Reserpine probably impairs the uptake of 5-HT at the level of the organelles (possibly by interfering with the association 5-HT/ATP), whereas imipramine seems to act preferentially on the cell membrane.