Inhibition of aggregation of rabbit and human platelets induced by adrenaline and 5-hydroxytryptamine by KB-R7943, a Na(+)/Ca(2+) exchange inhibitor.
1. We investigated the effect of KB-R7943, a Na(+)/Ca(2+) exchange inhibitor, on the aggregation response induced by adrenaline and 5-hydroxytryptamine (5-HT), alone or in combination in human and rabbit platelets in the presence or absence of ouabain. 2. KB-R7943 inhibited aggregation induced by the combination of adrenaline and 5-HT in a concentration-dependent manner. The IC(50) values of KB-R7943 were 4.2+/-2.0 or 3.0+/-0.7 microM with washed rabbit platelets with or without ouabain pretreatment, respectively. 3. In platelet-rich human plasma, the aggregation was biphasic. The IC(50) value of KB-R7943 was 17.2+/-4.4 microM for the first phase aggregation. 4. KB-R7943 did not inhibit the first phase of aggregation induced by adrenaline alone, or the monophasic aggregation induced by 5-HT alone. 5. The aggregation of rabbit platelets depended on the presence of K(+) in the medium, and K(+)-dependent and K(+)-independent Ca(2+) influx were observed in resting platelets. Ouabain treatment increased only the K(+)-dependent but not the K(+)-independent Ca(2+) influx. 6. KB-R7943 inhibited K(+)-dependent Ca(2+) influx with or without ouabain pretreatment, but not K(+)-independent Ca(2+) influx. 7. From these results, we conclude that KB-R7943 inhibits the adrenaline plus 5-HT induced aggregation of rabbit and human platelets by inhibiting K(+)-dependent Na(+)/Ca(2+) exchange (NCKX). Our results suggest that NCKX plays an important role in platelet aggregation.
Department of Pharmacology, School of Medicine, Fukushima Medical University, Hikari-ga-oka 1, Fukushima 960-1295, Japan. s-takano@cc.fmu.ac.jp
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Takano
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Kimura
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Ono
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002132:Calcium Radioisotopes; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D010974:Platelet Aggregation / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D012701:Serotonin / Q000494:pharmacology*; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013997:Time Factors
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D002132:Calcium Radioisotopes; D019831:Sodium-Calcium Exchanger; D012701:Serotonin; D013890:Thiourea; D011188:Potassium; D002118:Calcium; D004837:Epinephrine