Thrombin receptor-activating peptide sensitizes the human endothelial thrombin receptor
Kruse, H.J.; Mayerhofer, C.; Siess, W.; Weber, P.C.
American Journal of Physiology 268(1 Pt 1): C36-C44
1995
ISSN/ISBN: 0002-9513 PMID: 7840159 Document Number: 453346
Receptor-operated effects of alpha-thrombin and of the thrombin receptor-activating peptide TRAP-14 on Cytoplasmic Ca-2+ concentration ((Ca-2+)-i) were examined in fura 2-loaded endothelial cells. Experiments with hirudin showed that alpha-thrombin-induced Ca-2+ influx requires the continuous presence of active alpha-thrombin. YFLLRNP, known to antagonize alpha-thrombin- and TRAP-7-induced (Ca-2+)-i transients in platelets, did not antagonize (Ca-2+)-i transients in response to alpha-thrombin and TRAP-14 in human umbilical vein endothelial cells (HUVEC). Repetitive short-term stimulations with alpha-thrombin desensitized (Ca-2+)-i transients to subsequent stimulations with either alpha-thrombin or TRAP-14. In contrast, repeated short-term stimulations with TRAP-14 sensitized (Ca-2+), transients to subsequent stimulations with either agonist. Blockade of Ca-2+ influx by SKF-96365 abolished the sensitizing effect of TRAP-14. The results indicate distinct characteristics of platelet and endothelial thrombin receptors and suggest that alpha-thrombin and TRAP-14 activate the receptor differently. It appears that receptor desensitization occurs independently of TRAP-14 binding and, hence, tethered ligand binding to and activation of the receptor. Persistent receptor desensitization after alpha-thrombin seems to depend on both alpha-thrombin binding to the hirudin-like receptor domain and the irreversible proteolytic cleavage of the receptor. It does not involve the TRAP-14/tethered ligand binding site of the receptor. TRAP-14 primes the receptor by a mechanism mediated by Ca-2+ influx.