Proteolytic activation of a putative receptor leading to vasoconstriction and platelet aggregation.
Submandibular enzymatic vasoconstrictor (SEV), a member of the kallikrein family of enzymes, elicits biological effects by a proteolytically mediated mechanism. We studied 1) whether SEV is able to aggregate platelets and 2) whether SEV may activate a receptor other than the cloned thrombin receptor. SEV (10(-8)M) aggregated platelets, released ATP and increased intracellular Ca2+. Elastase treatment rendered human platelets unresponsive to SEV and thrombin (TH), but not to cathepsin G. In desensitization experiments performed with gamma-TH, after two successive additions of approximately 50 nM gamma-TH, a third dose elicited 15.8 +/- 3.4% of the initial response (n = 4), but platelets responded to approximately 20 nM SEV by 33.8 +/- 7.2% of control (p < 0.03 vs last response to gamma-TH). After desensitization to SEV (n = 4), the response to a third dose was 4 +/- 1.3% of control, but gamma-TH still induced 37.7 +/- 12.4% aggregation (p < 0.02 vs last response to SEV). Incubation of washed rabbit platelets with alpha-TH digested with elastase (10(-10) M TH added to 7 micrograms/ml elastase for 1 min) rendered them unresponsive to additional challenges with TH, but they still responded to an equipotent dose of SEV (2.7 x 10(-9) M) by 86 +/- 48% of control. In isolated rabbit aortic rings contracted with 10(-6) M norepinephrine (NE) to 42 +/- 3% of maximum. SEV (2.8 x 10(-8) M) caused further contraction to 87 +/- 4%. In contrast, alpha-TH (1.6 x 10(-7) M) tended to relax both NE- and SEV-contracted rings by 14 +/- 2 and 16.2 +/- 2%, respectively (n = 3 each). We concluded that part of the platelet-aggregating effect of SEV may be mediated by activation of a receptor(s) different from that of TH.
Carbini
L A
LA
Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan 48202, USA.
Mindroiu
T M
TM
Kitamura
S
S
Scicli
A G
AG
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000494:pharmacology*
D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D012697:Serine Endopeptidases; C067805:submandibular enzymatic vasoconstrictor; D002118:Calcium