Transformation and motility of human platelets: details of the shape change and release reaction observed by optical and electron microscopy.

Abstract

Blood platelets from 10 normal buman subjects were examined with a sensitive differential interference contrast (DIC) microscope. The entire transformation process during adhesion to glass was clearly visible and was recorded cinematographically, including disk to sphere shape change, sessile protuberance formation, pseudopodia extension and retraction, and spreading, ruffling, and occasional regression of the hyalomere. Exocytosis of intact dense bodies could be observed either by DIC microscopy, or by epifluorescence microscopy in platelets stained with mepacrine. Details of fluorescent flashes indicated that dense bodies usually release contents extracellularly, but may do so intracytoplasmically under the influence of strong, short-wavelength light on some mepacrine-stained platelet preparations. Release of 1 or more dense bodies left a crater of variable size on the upper granulomere surface. Such craters represented the surface component of the open canalicular system; their formation and disappearance could be directly observed. Because these techniques permit quantitation of several motility parameters which were not readily observable by other techniques, high extinction DIC microscope examination may become a rapid and useful method of studying congenital and acquired platelet disorders. Many platelet transformation features were confirmed and extended by scanning electron micrographs. These could be interpreted by reference to time-lapse films of living platelets.