Different effects of thrombin receptor activation on endothelium and smooth muscle cells of human coronary bypass vessels. Implications for venous bypass graft failure.
BACKGROUND
Thrombin is implicated in coronary bypass graft disease; it cleaves its receptor's extracellular N-terminal domain and unmasks a new N-terminus as a tethered ligand. We studied the effects of thrombin receptor activation in human internal mammary artery (IMA) and saphenous vein (SV).


RESULTS
To study the effects of thrombin receptor activation on vasomotion, isolated blood vessels were suspended for isometric tension recording, and the effects on cell proliferation were studied in cultured smooth muscle cells (SMCs) of IMA and SV. Thrombin receptor expression in IMA and SV was analyzed by reverse transcription polymerase chain reaction and immunohistology. Receptor function was studied by analyzing the activation of mitogen-activated protein kinase (p42MAPK). In IMA thrombin evoked endothelium-dependent relaxations (65 +/- 5%) that were mimicked by thrombin receptor agonist peptide (TRAP) and reduced by the thrombin inhibitors recombinant (r-) hirudin and D-Phe-Pro-Arg-chloromethyl ketone (PPACK) (P < .05). In SV thrombin caused contractions (36 +/- 5% of 100 mmol/L KCl) that were inhibited by r-hirudin or PPACK (P < .05) but not mimicked by TRAP. In SMCs thrombin induced more pronounced [3H]thymidine incorporation (inhibited by r-hirudin or PPACK) in SV than IMA (P < .05), but activation of p42MAPK was similar in both vessels. TRAP induced weaker activation of p42MAPK than thrombin and did not stimulate [3H]thymidine incorporation in SMCs of SV or IMA. Immunohistology and RT-PCR demonstrated that the endothelium and SMCs of IMA and SV express thrombin receptor.


CONCLUSIONS
Functional thrombin receptors are present on endothelium and SMCs of IMA and SV. Endothelial thrombin receptors mediate relaxation in IMA but not SV. Thrombin causes much more pronounced contraction and proliferation in SMCs of SV than IMA independent of tethered receptors, suggesting other thrombin receptors exist. These differences of thrombin receptor activation in IMA and SV may be important in the development of and therapy for graft disease.
Yang
Z
Z
Department of Cardiology, University Hospital, Inselspital Bern, Switzerland.
Ruschitzka
F
F
Rabelink
T J
TJ
Noll
G
G
Julmy
F
F
Joch
H
H
Gafner
V
V
Aleksic
I
I
Althaus
U
U
Lüscher
T F
TF
D000590:Amino Acid Chloromethyl Ketones / Q000627:therapeutic use; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology; D002478:Cells, Cultured; D001026:Coronary Artery Bypass; D004261:DNA Replication; D004730:Endothelium, Vascular / Q000187:drug effects*; D004789:Enzyme Activation; D024764:Hirudin Therapy; D006629:Hirudins / Q000031:analogs & derivatives; D006801:Humans; D007387:Internal Mammary-Coronary Artery Anastomosis; D019950:Mitogen-Activated Protein Kinase 1; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000627:therapeutic use; D010766:Phosphorylation / Q000187:drug effects; D011475:Prosthesis Failure; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D018179:Receptors, Thrombin / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D012501:Saphenous Vein / Q000637:transplantation; D013917:Thrombin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology
D000590:Amino Acid Chloromethyl Ketones; D006629:Hirudins; D009842:Oligopeptides; D010446:Peptide Fragments; D018179:Receptors, Thrombin; C096900:thrombin receptor-activating peptide SFLLRNPNDKY; C062510:hirugen; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D013917:Thrombin; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone