Rapid platelet morphological changes visualized by scanning‐electron microscopy: kinetics derived from a quenched‐flow approach

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Abstract
Human platelet activation is accompanied by distinct morphological changes from disc-shaped cells to more rounded particles with multiple blebs or pseudopodia. A quenched-flow approach was used to follow the kinetics and nature of these morphological events. Scanning-electron micrographs revealed very rapid alterations in platelet shape. At 0.5 s after activation with ADP or thrombin, the number of resting disc-shaped particles was nearly halved and short blebbed forms were maximal at 0.5 s. By 1.7 s about 60% of particles were in the fully activated or multiple-blebbed form. The Ca ionophore A-23187 caused slightly slower effects. Adrenaline [epinephrine] was much less potent, with about 14% of platelets becoming fully activated by 10 s. Control experiments showed only small changes in particle morphology when unactivated platelets were pumped through the reaction tubing and then quenched in glutaraldehyde. The resistive volume of platelets increased by 0.42 flat 0.5 s after ADP stimulation and was essentially independent of variations in particle shape. The quenched-flow approach can provide new information about platelet function and that morphological changes begin earlier than previously thought.

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