Effects of concanavalin A on 5-hydroxytryptamine uptake by rabbit blood platelets and on their ultrastructure.
1. Effects of concanavalin A (Con A) and other lectins on 5-hydroxytryptamine (5-HT) uptake by rabbit blood platelets and on their ultrastructure were studied. 2. Uptake of [3H]-5-HT by platelets was decreased by application of Con A, E-PHA (lectin from Phaseolus vulgaris) and lentil-PHA (lectin from Lens culinaris), but not by wheat germ agglutinin (WGA). Con A induced specific changes in the ultrastructure of platelets, causing (i) a change in external appearance from a discoid to an irregularly spherical shape, (ii) re-arrangement of the canalicular system and formation of a concentric structure. These effects of Con A on platelets were antagonized by pretreatment with alpha-methyl-D-mannoside (alpha-MM), a specific inhibitor of Con A binding to glycoprotein. 3. The inhibition of 5-HT uptake by Con A was antagonized by colchicine, vinblastine and sodium nitroprusside (SNP), but not by cytochalasin B. 4. Theophylline, papaverine and dibutyryl cyclic adenosine 3',5'-monophosphate (db cyclic AMP) antagonized the effect of Con A on 5-HT uptake, but dibutyryl cyclic guanosine 3',5'-monophosphate had no effect. Theophylline and db cyclic AMP did not influence the effect of Con A on the ultrastructure of platelets. 5. It is suggested that binding of Con A to specific receptor glycoproteins can inhibit the 5-HT uptake system of platelets. Microtubules, contractile protein and the membrane adenylate cyclase system of platelets may also be regulatory factors in this mechanism.
D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D003994:Bucladesine / Q000494:pharmacology; D003208:Concanavalin A / Q000494:pharmacology*; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008766:Methylmannosides / Q000494:pharmacology; D010208:Papaverine / Q000494:pharmacology; D010835:Phytohemagglutinins; D011817:Rabbits; D012701:Serotonin / Q000097:blood*; D013806:Theophylline / Q000494:pharmacology; D013997:Time Factors
D008766:Methylmannosides; D010835:Phytohemagglutinins; D003208:Concanavalin A; D003995:Dibutyryl Cyclic GMP; D012701:Serotonin; D003994:Bucladesine; D013806:Theophylline; D010208:Papaverine