Different effects of endothelin-3 on the Ca2+ discharge induced by agonists and Ca(2+)-ATPase inhibitors in human platelets.
1. The present study demonstrates that endothelin-3 (ET-3), previously shown to attenuate thrombin-evoked aggregation of human platelets, delayed the dose-dependent aggregatory response to thapsigargin (Tg). As this Ca(2+)-ATPase inhibitor induces platelet activation in part through the depletion of internal Ca(2+)-stores, we examined the influence of ET-3 on Ca2+ discharge from internal pools. 2. Cytosolic Ca2+ concentration was evaluated with Fura-2 in the absence of Ca2+ influx. Platelet preincubation for 15 min with 5 x 10(-7) M ET-3 decreased the Ca2+ release evoked by thrombin and U46619, a thromboxane-mimetic. However, ET-3 did not affect Ca2+ movements induced by 1 microM ADP. Addition of Tg (0.5 to 5 microM) to resting platelets induced a cytosolic [Ca2+] rise with concentration-dependent increase of the initial rate and decrease of the time to reach the peak. ET-3 slowed down these dose-dependent effects with a more marked influence on the responses induced by low concentrations of Tg. 3. ET-3 did not modify the Ca2+ response to another Ca(2+)-ATPase inhibitor, 2,5-di-(tert-butyl)-1,4-benzohydroquinone(tBuBHQ). The thromboxane A2 receptor antagonist, SQ 29548, reduced by 53% the calcium signal evoked by 1 microM Tg, which became similar to that induced by 15 microM tBuBHQ. Under these conditions, the ET-3 effects were suppressed. A subsequent addition of thrombin induced a substantial further Ca2+ increase which was again sensitive to ET-3. 4. ET-3 attenuates Ca2+ mobilization from an internal pool dependent on the stimulation of thrombin and thromboxane A2 receptors and insensitive to the direct effect of Ca2+-ATPase inhibitors. The small but significant inhibitory effect of ET-3 leads us to propose that endothelin-3 acts as a modulator of platelet activation.
Astarie-Dequeker
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CNRS URA 1482 Necker Medical School, Paris, France.
Korichneva
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Devynck
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D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002118:Calcium / Q000097:blood*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D016232:Endothelins / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated; D016257:Fura-2; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D066298:In Vitro Techniques; D010974:Platelet Aggregation / Q000187:drug effects; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D017466:Receptors, Endothelin / Q000819:agonists*; D017482:Receptors, Thromboxane / Q000037:antagonists & inhibitors; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013917:Thrombin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000975:Antioxidants; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002120:Calcium Channel Agonists; D016232:Endothelins; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D006873:Hydroquinones; D011450:Prostaglandin Endoperoxides, Synthetic; D017466:Receptors, Endothelin; D017482:Receptors, Thromboxane; D013729:Terpenes; D014662:Vasoconstrictor Agents; C019359:2,5-di-tert-butylhydroquinone; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C045749:SQ 29548; D013917:Thrombin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2