Tannic acid-glutaraldehyde fixation reveals calcium ionophore-induced changes in rabbit polymorphonuclear leukocyte membranes.

TAG fixation of normal and Ca2+ ionophore-treated rabbit polymorphonuclear leukocytes (PMN) has revealed membrane components not apparent with conventional glutaraldehyde fixation. These included a 30 A external electron-dense coating on untreated cells. A somewhat thicker coat (40 A) was observed in ionophore-treated, nondegranulating PMN. In ionophore-treated, degranulating PMN, a 65 A cell membrane coat was observed. A similar coat was observed on the inner side of the membrane of some azurophil-type granules, but the electron density and thickness were not so pronounced. Cytoplasmic granules were often closely apposed and often protruded outward at the plasma membrane. Extracellular lamellae, sometimes stacked apposed to the plasma membrane, possibly represent remnants of intense granule extrusion. Sequential degranulation of the respective granules was not apparent.