Distinct receptors and signaling pathways in alpha-thrombin- and thrombin receptor peptide-induced vascular contractions.
The vasoactive mechanisms of the serine protease alpha-thrombin were examined in isolated coronary arteries from dogs. In resting coronary arteries with endothelium, alpha-thrombin caused concentration-dependent contractions that were characterized by an initial transient relaxation followed by slowly developing sustained contractions. The vascular actions of alpha-thrombin were mimicked by the thrombin receptor-activating peptide (TRAP) SFLLRNP, a synthetic peptide based on the cleaved terminus of the thrombin receptor domain. Treatment of the arteries with N omega-nitro-L-arginine or removal of endothelium abolished the transient relaxations and enhanced the contractions, indicating that the transient relaxations were mediated by the concurrent release of endothelium-derived nitric oxide. alpha-Thrombin that had been catalytically inactivated with the irreversible inhibitor by use of D-Phe-Pro-Arg-chloromethyl ketone did not cause contractions, indicating the requirement of proteolytic cleavage by alpha-thrombin to induce contractions. In contrast to TRAP, alpha-thrombin-induced contractions were blocked by hirudin (a specific thrombin inhibitor), nifedipine and diltiazem (Ca2+ channel blockers), or staurosporine and calphostin C (protein kinase C inhibitors). Unlike alpha-thrombin, which undergoes homologous desensitization, TRAP failed to cause desensitization to subsequent stimulation by alpha-thrombin or TRAP. These observations support the hypothesis that vasoactive actions of alpha-thrombin are mediated by a mechanism that involves cleavage at the active site to expose a new NH2 terminus that activates the thrombin receptor. Further, the dissociation between alpha-thrombin and the synthetic receptor peptide in signal transduction and dissimilar desensitizing properties suggest the existence of distinct thrombin receptor subtypes and/or signaling events in vascular smooth muscle.
Tesfamariam
B
B
Department of Pharmacology, Bristol-Myers Squibb Research Institute, Princeton, NJ 08543.
D000818:Animals; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004285:Dogs; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology*; D018179:Receptors, Thrombin; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology*
D010446:Peptide Fragments; D018179:Receptors, Thrombin; C072032:thrombin receptor peptide (42-55); D013917:Thrombin