Inhibitory effect of EGTA on serotonin transport into rabbit blood platelets: possible involvement of the glycoprotein IIb/IIIa complex.
We reported previously that serotonin (5-HT) transport was attenuated by treatment of platelets with EGTA, and that this inhibitory effect of EGTA was restored by CaCl2. In the present study, the inhibitory effect of EGTA was found to be uncompetitive, and no inhibitory effect was observed when EGTA was added at 20 degrees C. Genistein and thyrphostin A47, both protein tyrosine kinase inhibitors, inhibited Ca(2+)-induced restoration of 5-HT transport. In contrast, the protein tyrosine phosphatase inhibitor phenylarsine oxide significantly augmented Ca(2+)-induced restoration of 5-HT transport. These results might support the hypothesis that the glycoprotein (GP) IIb/IIIa complex, a platelet membrane integrin protein, might regulate 5-HT transport into blood platelets. It is conceivable that Ca2+ chelation by EGTA might cause temperature-dependent dissociation of the GP IIb/IIIa complex, which results in the reduction of 5-HT transport. Rearrangement of the GP IIb/IIIa complex by replenishment of the Ca2+ binding sites might restore the EGTA-induced reduction of 5-HT transport.
Nishio
H
H
Department of Pharmacology, Hiroshima University School of Medicine, Japan.
Kagawa
T
T
Nezasa
K
K
Nakata
Y
Y
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002109:Caffeic Acids / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology*; D019833:Genistein; D007529:Isoflavones / Q000494:pharmacology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011817:Rabbits; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013696:Temperature; D020032:Tyrphostins
D002109:Caffeic Acids; D002352:Carrier Proteins; D002614:Chelating Agents; D007529:Isoflavones; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D012702:Serotonin Antagonists; D020032:Tyrphostins; C060152:tyrphostin 47; D004533:Egtazic Acid; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D002118:Calcium