Summary
A simultaneous investigation of the kinetics of serotonin (5 HT) uptake and of binding
sites was carried out in the platelets of normal subjects and of 10 patients affected
with various types of myeloproliferative disorders (MD). The 5 HT uptake was analysed
according to the Lineweaver-Burk and the Eadie-Hofstee methods. With the two methods,
the patient’s platelets exhibited a dramatic reduction of the Vi max and of the Km;
in some patients the Eadie-Hofstee analysis revealed that a passive diffusion phenomenon
is superimposed on the active 5 HT uptake at least for the higher concentration used.
The binding data were analysed with the Scatchard method. Two classes of binding sites
(high affinity - low capacity, low affinity - high capacity) were found in normal
subjects and patients. Pharmacological studies with imipramine, a specific inhibitor
of 5 HT uptake, suggested that both the sites are involved in 5 HT uptake. The number
of both binding sites was significantly decreased in patient’s platelets while the
affinity constants of these binding sites were not significantly reduced in comparison
with those of the control subjects. No correlations were found between Vi max, Km
and the number of binding sites. These results suggest that a reduction in the number
of platelet membrane acceptors for 5 HT commonly occurs in myeloproliferative disorders
but does not provide a full explanation of the uptake defect.
Keywords
Myeloproliferative disorders - Platelet serotonin uptake - Platelet serotonin binding
sites
