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Antibodies to pp60v-arc and phosphotyrosine were introduced into rabbit platelets using an electropermeabilization technique. The presence of these antibodies inside platelets was detected by flow cytometry. Platelet-activating factor (PAF)-stimulated phospholipase C activity (inositol phosphate production) and aggregation were dramatically inhibited in platelets transjected with either of these antibodies. Incubation of these antibodies with intact cells (i.e. nonpermeabilized) or electrotransjection of several nonspecific antibodies/agents (e.g. goat anti-mouse IgG, mouse serum, human platelet glycoprotein Ib monoclonal antibody, and fetal calf serum) into platelets had no effect on the PAF responses. trpE (another isotype-matched control antibody of pp60v-src) and pp56lck polyclonal antibody (another src-related kinase not present in platelets) also had no effect on PAF-induced aggregation and inositol phosphate production in permeabilized platelets. This indicates that the effect of internalized pp60v-src antibody is direct and specific in platelets. Stimulation of platelets by PAF increased the association and phosphorylation of both pp60c-src (60 kDa) and phospholipase C gamma 1 (145 kDa). This study provides the first evidence in platelets for a direct and specific involvement of pp60c-src in PAF-mediated phospholipase C activation and aggregation response.
Dhar et al. (Tue,) studied this question.