Activators of protein kinase C decrease serotonin transport in human platelets.
Treatment of human platelets with activators of protein kinase C (PKC) for 5-20 min resulted in substantial reductions in the rate of platelet serotonin (5-HT) transport. The mean Vmax observed after 5 min treatment with 1 microM 4-beta-12-tetradecanoylphorbol 13-acetate (beta-TPA) was 66% (n = 16, P = 0.0001) of the control value. 5 min of treatment with 1 microM mezerein reduced uptake to 78% (n = 3, P = 0.01) of control. Both beta-TPA and mezerein had little effect on the Km of transport and had EC50 values of approx. 100 mM when a 20-min treatment period was used. The maximum effects of both were reached at approx. 20 min and could be blocked with staurospine. The beta-TPA effect was stereospecific, as alpha-TPA did not alter platelet 5-HT uptake. Although the PKC activators may have altered transmembrane ion-gradients for Na+ and Cl-, which are co-transported with 5-HT, minimizing ion-gradient changes had little effect on the observed reductions in transport. The PKC activators also had little or no effect on platelet 5-HT release or on the number (Bmax) of 5-HT transporters expressed at the platelet surface. The data indicate that PKC activation may down-regulate the activity of the 5-HT transporter in platelets. Apparently, most of this effect is mediated through mechanisms other than changes in ion-gradients, reductions in the number of available transporters, or increased 5-HT release. The apparent regulation of 5-HT transport by PKC may have important implications in platelet and neuronal functioning.
Anderson
G M
GM
Child Study Center, Yale University School of Medicine, New Haven, CT 06510.
Horne
W C
WC
D000470:Alkaloids / Q000494:pharmacology; D001692:Biological Transport; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D004224:Diterpenes; D004789:Enzyme Activation; D006801:Humans; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D019311:Staurosporine; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D004224:Diterpenes; D013729:Terpenes; D012701:Serotonin; C011309:mezerein; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate