The uptake of 6-methoxy-1,2,3,4-tetrahydro-beta-carboline and its effect on 5-hydroxytryptamine uptake and release in blood platelets

The uptake of 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeOTHBC, 5-methoxytryptoline) by rabbit blood platelets was studied by using 3H-labelled compound. A high rate active uptake (Km 6.6 micron), which was inhibited by 5-hydroxytryptamine (5-HT) and cinnanserine, and a slow rate uptake, not inhibited by 5-HT were observed. The intracellular distribution of 3H-6-MeOTHBC in platelets clearly differed from that of 14C-5-HT. 6-MeOTHBC also competitively inhibited the high-rate active (but not the slow passive) uptake of 14C-5-HT, being more active than 5-HT itself. The spontaneous release of the newly taken-up 14C-5-HT from platelets was increased only with high concentrations of 6-MeOTHBC.