Phosphorus and divalent cations in dog, rabbit, and human platelet dense bodies as deduced from electron microprobe studies of air-dried whole mounts.

Dense bodies have been examined by electron microprobe techniques in air-dried whole mounts of dog, rabbit, and human platelets. On the basis of measurement of the intensities of the X-rays produced when dense bodies are probed for 100 seconds, dog and rabbit platelet dense bodies contain on the average less phosphorus and calcium, but more magnesium, than do human platelet dense bodies. Dense bodies of dog and rabbit platelets thus appear to resemble more closely those of pig platelets than those of human platelets.

Evaluation of the utility of air-dried whole mounts for quantitative electron microprobe studies of platelet dense bodies.

A variety of electronmicroscope techniques have been used to examine how the air-drying process may affect the dense bodies in whole mounts of platelets. (a) Selected-area-diffraction and electron microprobe studies suggest that the air-drying process can result in the formation of crystalline precipitates of sodium chloride on grid films and platelets. However, no crystals were detected in the calcium-and-phosphorus-containing matrix of dense bodies. (b) Tilting studies show that dense bodies in human platelets are spherical or ellipsoidal in shape. Dense bodies in rabbit platelets, in contrast, appear flattened in a horizontal plane. (c) Human-platelet dense bodies probed with a small (20 nm diameter) spot vary widely in their peak/background ratios for calcium and phosphorus-a finding that suggests that the two elements may not be evenly distributed throughout the dense-body matrix. Nevertheless, when dense bodies are probed with a larger (200 nm diameter) spot, they do not appear to differ appreciably among themselves in their calcium or phosphorus content. The data suggest that with human platelets, air drying may be a preparative procedure which permits comparison by microprobe techniques of dense-body matrix content in platelet populations.