Selective inhibition of collagen-induced arachidonic acid liberation by 1-(5-iodonaphthalene-1-sulphonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7), a myosin light chain kinase inhibitor, in washed rabbit platelets.
Effects of myosin light chain (MLC) kinase inhibitor ML-7 [1-(5-iodonaphthalene-1-sulphonyl)-1H-hexahydro-1,4-diazepine hydrochloride] and protein kinase C inhibitor H-7 [1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydro-chloride] on collagen-induced platelet activation were investigated in washed rabbit platelets. Upon stimulation with collagen (1 microg/mL), H-7 decreased protein kinase C-mediated pleckstrin phosphorylation, but had no inhibitory effect on thromboxane (TX) A2 formation or platelet aggregation. In contrast, ML-7 produced a concentration-dependent inhibition of the collagen-induced platelet aggregation and TXA2 formation by preventing arachidonic acid (AA) liberation from membrane phospholipids. However, ML-7 had little effect on AA liberation induced by thrombin, Ca2+ ionophore A-23187 or melittin, suggesting that ML-7 may affect the signal transduction pathway specific for collagen-induced AA liberation, without direct inhibition of phospholipase A2 activity. In indomethacin-treated platelets, collagen caused MLC phosphorylation and AA liberation in the absence of a significant increase in intracellular Ca2+ concentration ([Ca2+]i) or protein tyrosine phosphorylation. ML-7 inhibited both MLC phosphorylation and AA liberation induced by collagen in indomethacin-treated platelets. These results demonstrate that MLC phosphorylation and AA liberation are early events detectable in collagen-stimulated platelets, and suggest that ML-7 inhibits these early steps of collagen-induced signal transduction pathway in rabbit platelets.
Matsuoka
I
I
Department of Pharmacology, Fukushima Medical College, Japan.
Nakahata
N
N
Nakanishi
H
H
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001381:Azepines / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors*; D009281:Naphthalenes / Q000494:pharmacology*; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects; D011817:Rabbits; D014443:Tyrosine / Q000378:metabolism
D001381:Azepines; D004791:Enzyme Inhibitors; D009281:Naphthalenes; C070571:ML 7; D016718:Arachidonic Acid; D014443:Tyrosine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D003094:Collagen; D009219:Myosin-Light-Chain Kinase; D002118:Calcium