Relationship between internal Na + -K + and the accumulation of 14 C-5-hydroxytryptamine by rat platelets.

1. 5-Hydroxytryptamine (5-HT) transport has been investigated in rat blood platelets poisoned with dinitrophenol-sodium fluoride or ouabain.2. The inhibition of transport produced by different concentrations of the metabolic inhibitors has been correlated with changes in the internal Na(+) and K(+) concentrations of the platelets.3. Platelets poisoned in a high K(+) medium maintained a high internal K(+) concentration in the absence of cellular metabolism. When transferred to Krebs solutions containing different concentrations of Na(+) they accumulated 5-HT by a process that was related to the magnitudes of the internal and external Na(+) concentrations.4. The results are consistent with the hypothesis that the spontaneous movement of ions through the platelet membrane is capable of providing, at least in part, the energy requirements for 5-HT transport.