Measurements of the G-/F-actin equilibrium in ADP-stimulated human platelets.

The amounts of the different forms of actin (G-actin, F-actin) can be measured biochemically following lysis of the cells by the DNase I inhibition assay. The existing methodology for studying G-actin in unstimulated platelets was found to be inappropriate for studies during ADP-induced platelet activation. However, this problem was overcome by a simple modification of the procedure in which formaldehyde was added to the buffer used to lyse the activated platelets. Using this modification the G-actin values obtained immediately after lysis did not change during storage of the lysates on ice for more than 30 minutes. The results show rapid conversion of G-actin to F-actin in association with the shape change during ADP-stimulated activation. Examination of unstimulated platelets using the modified procedure enabled identification of a pool of actin that is rapidly dissociated to G-actin in the absence of formaldehyde, the existence of which had not previously been recognised.