Shape changes and reduced calcium level in the surface membrane region of human platelets exposed to manganese in vitro.

The effect of exogenous manganese ions upon human platelets in vitro has been studied. Morphological changes reported include the loss of discoid shape, increase in filopodia and close apposition of platelet surfaces. Electron microscope X-ray microanalysis of thin-sectioned material revealed a significant decrease in the bound calcium levels of the surface membrane as a result of manganese treatment. Analysis of whole platelet homogenates using atomic absorption spectrophotometry indicated that the total internal platelet calcium content had increased significantly. It is suggested that manganese induces the observed changes by displacing calcium from the regulatory system of an actomyosin-like protein complex at the periphery of the platelet.