The effects of glutaraldehyde and formaldehyde fixation on the retention and subcellular location of [3H]5-hydroxytryptamine in rabbit platelets: a study using liquid scintillation counting and E.M. autoradiography.

The retention and loss of [3H]5-hydroxytryptamine (5-HT) from rabbit platelets during fixation was studied using liquid scintillation counting and quantitative electron-microscopic autoradiography. The results were at variance with previously reported data on human platelets. Following treatment of the platelets with either 2.0% formaldehyde or 2.5% glutaraldehyde for 2 min or 1 h it was found that a significantly increased proportion of the radioactivity was lost from treated as compared with untreated platelets. Using a method of analysis which accounts for cross-scatter of decay particles between cell compartments, electron-microscopic autoradiography revealed that 50% of the radioactivity following incubation of platelets with [3H]5-HT was associated with dense bodies and 30% in the cytoplasm when fixation was in formaldehyde or glutaraldehyde. The only major difference in the labelling pattern was that whereas glutaraldehyde appeared to retain no activity in the surface connected system the latter contained 12% of total retained activity following fixation with formaldehyde.