Shape change in human platelets: measurement with a channelyzer and visualisation by electron microscopy

The increase in median platelet volume (MPV) that occurs following the addi tion of various agonists can be recorded by high-resolution channelyzers. H owever, this increase in MPV may not represent the platelet shape change (P SC), an early phase of platelet activation characterised by the formation o f pseudopodia, We therefore compared the NPV after adding various agonists (serotonin, ADP or a thromboxane A(2) analogue) with scanning electron micr ographs (EM) of the platelets in the same sample, Saline alone did not incr ease the MPV or alter platelet morphology. In contrast, the selected agonis ts altered both the MPV and EM. Adrenaline (5.0 mu mol/l) alone did not inf luence either of these indices of platelet activation. However, when a lowe r concentration of adrenaline (0.2 mu mol/l) was added in combination with a dose of serotonin (0.02 mu mol/l) that did not affect the MPV on its own, the measured MPV increased significantly and the EM showed pseudopodia for mation. Because the channelyzer method is reproducible and suited to serial measurements of the MPV, it ma become a useful toot for the investigation of platelet activation.