engleski

Serotonin transporter : studies on platelet model in rats and humans

Serotonin transporter (5HTt) occupies the central position in the regulation of 5HT synaptic activity in the brain. Structural identity of this protein and its peripheral counterpart in blood platelet membrane has been recently demonstrated. The easy accessible platelets have become an important model for this mechanism. In this work we summarized our studies on platelet 5HTt in rats and humans, undertaken in order to comparatively characterize kinetic performances of both proteins, relate them to serotonin levels in platelets and analyze the mechanisms underlying the genetic control of transporter kinetics. Clinical studies were started with the aim to evaluate the suitability of this peripheral mechanism as a biological marker in behavioral syndromes related to serotonergic dysfunction. Full kinetic analyses of serotonin transporter, using radioactive method and fluorometric measurements of platelet serotonin levels were performed in a group of Zgr: WIstar rats from standard breeding and in animals genetically selected for these traits. Analogous measurements were performed in healthy volunteers and patients. Total RNA was isolated from platelets of rats and humans by guanidinium-acid-phenol extraction method and 5HTt mRNA was identified by the use of Northern blot analysis. Comparative kinetic analyses of 5HTt revealed higher affinities of platelet transporter in rats with analogous differences in maximal velocities, so that the efficiency of rat transporter (kinetic product: Vmax/Km) was about four times higher than its counterpart on human platelets. Similarly, the level of serotonin in rat platelets was about three times higher when compared to human platelets. This points to the interrelation between 5HT transporter and 5HT level in platelets, as well as to the maintenance of serotonin homeostasis in rats at the higher level than in humans. Analyses of platelet 5HTt in sublines of animals with genetically high or low platelet serotonin level demonstrated analogous differences in transporter kinetics. Studies of gene expression for 5HTt indicate differences in platelet mRNA between sublines in such way that platelets with high-efficiency transporter contain significantly more 5HTt mRNA than the low- efficiency ones.

5HT transporter ; platelet 5HT ; transporter mRNA

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