ELECTROROTATION MEASUREMENTS OF DIAMIDE-INDUCED PLATELET ACTIVATION CHANGES

Electrorotation is a special dielectric spectroscopic technique capable of measuring the polarizability of single platelets. The rotational speed of the particles is recorded as a function of the frequency of the applied rotating electric field. As previously shown, the speed of electrorotation in the range of the first characteristic frequency (anti-field rotation) decreased upon activation and was correlated with [C-14]serotonin release and an increase of the TMA-DPH-induced fluorescence. Diamide incubation induced morphological changes in control platelets. These changes were accompanied by a shift of the first characteristic frequency of electrorotation toward higher values and a parallel increase of the anti-field rotation. This was explained by a decrease of membrane conductivity and by the changed polarizability of platelet interior due to the observed internal platelet structure changes. Diamide inhibited activation assessed by both electrorotation and TMA-DPH fluorescence in the case of all activators except the ionophore A 23187. Because diamide largely inhibited the A 23187-induced serotonin release, it was concluded that, despite the diamide treatment, the direct increase of cytoplasmic Ca2+ was still able to induce membrane conductivity changes accessible by electrorotation, but this did not complete the final release step of the activation process.