Tannic acid effect on membrane of cell surface origin in guinea pig megakaryocytes and platelets.

Plasma membranes in isolated guinea pig megakaryocytes and washed platelets are poorly stained with the usual methods used to outline cell membranes. The addition of tannic acid and calcium to the initial fixative is useful to enhance electron density of all surface-derived membrane systems in these cells. The method described here shows that the increased electron denisty of membrane after fixation in the presence of tannic acid occurs both at the cell surface and along the invaginated membrane systems.