Activation of rabbit platelets by Ca2+ influx and thromboxane A2 release in an external Ca(2+)-dependent manner by zooxanthellatoxin-A, a novel polyol.
1. Zooxanthellatoxin-A (ZT-A), a novel polyhydroxylated long chain compound, isolated from a symbiotic marine alga Simbiodinium sp., caused aggregation in rabbit washed platelets in a concentration-dependent manner (1-4 microM), accompanied by an increase in cytosolic Ca2+ concentration ([Ca2+]i). 2. ZT-A did not cause platelet aggregation or increase [Ca2+]i in a Ca(2+)-free solution, and Cd2+ (0.1-1 mM), Co2+ (1-10 mM) and Mn2+ (1-10 mM) inhibited ZT-A-induced aggregation. SK&F96365 (1-100 microM), a receptor operated Ca2+ channel antagonist, and mefenamic acid (0.1-10 microM), a non-specific divalent cation channel antagonist, inhibited platelet aggregation and the increase in [Ca2+]i induced by ZT-A. 3. Indomethacin (0.1-10 microM), a cyclo-oxygenase inhibitor, and SQ-29548 (0.1-10 microM), a thromboxane A2 (TXA2) receptor antagonist, inhibited platelet aggregation and the increase in [Ca2+]i induced by ZT-A. 4. Methysergide (0.01-1 microM), a 5-HT2 receptor antagonist, inhibited ZT-A-induced platelet aggregation but did not affect the increase in [Ca2+]i induced by ZT-A. 5. Tetrodotoxin (1 microM), a Na+ channel blocker and chlorpheniramine (1 microM), a H1-histamine receptor antagonist, neither affected ZT-A-induced platelet aggregation nor the increase in [Ca2+]i induced by ZT-A. 6. Genistein (1-100 microM), a protein tyrosine kinase inhibitor, and staurosporine (0.01-1 microM), a protein kinase C inhibitor, also inhibited ZT-A-induced platelet aggregation. 7. The present results suggest that ZT-A elicits Ca(2+)-influx from platelet plasma membranes. The resulting increase in [Ca2+]i subsequently stimulates the secondary release of TXA2 from platelets. Furthermore, the response to ZT-A may be associated with tyrosine phosphorylation.
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Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Sendai, Japan.
Nakahata
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Nakamura
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H
Murai
A
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Ohizumi
Y
Y
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002744:Chlorpheniramine / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated; D019833:Genistein; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007529:Isoflavones / Q000494:pharmacology; D008297:Male; D008387:Marine Toxins / Q000737:chemistry / Q000633:toxicity*; D008784:Methysergide / Q000494:pharmacology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011090:Polyenes / Q000737:chemistry / Q000633:toxicity*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011817:Rabbits; D012702:Serotonin Antagonists / Q000494:pharmacology; D019311:Staurosporine; D013779:Tetrodotoxin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013929:Thromboxane B2 / Q000378:metabolism
D000470:Alkaloids; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002121:Calcium Channel Blockers; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D005231:Fatty Acids, Unsaturated; D006634:Histamine H1 Antagonists; D006834:Hydrazines; D007093:Imidazoles; D007529:Isoflavones; D008387:Marine Toxins; D010975:Platelet Aggregation Inhibitors; D011090:Polyenes; D012702:Serotonin Antagonists; C081400:zooxanthellatoxin A; D002744:Chlorpheniramine; D013779:Tetrodotoxin; D013929:Thromboxane B2; D013928:Thromboxane A2; C045749:SQ 29548; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D019311:Staurosporine; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium; D007213:Indomethacin; D008784:Methysergide