Increased histamine content in Ca2+-ionophore A23187-activated human blood platelets

Stimulation of human blood platelets with Ca2+-ionophore A23187 at the concentrations of 0.5, 1, 2 and 3 micromol/ litre increased the total platelet histamine content from 25 ng (resting platelets) to 35, 40, 42 and 47 ng/10(8) platelets, respectively. The maximum rise was 90% , while in the presence of thrombin (0.01-1 NIH U/ml) or phorbol 12-myristate 13-acetate (PMA) (10-100 nmol/l) histamine content rose maximally by 40%. Ionophore induced a histamine increase in the same concentration range as that needed to induce platelet aggregation and liberation of [3H]-arachidonic acid. Decrease of temperature from 37 to 0 degrees C or inhibitors of platelet functions, such as acetylsalicylic acid (1 mmol/litre) or [H1]-histamine receptor antagonist Dithiaden (0.1 mmol/litre), 1 inhibited histamine liberation from A23187- stimulated platelets, but did not affect the total rise in histamine content. The presented results indicate that, similarly as with other stimuli, Ca2+-ionophore A23187 activation of human blood platelets is accompanied by histamine synthesis.