Studies on the relevance of microtubules and of microfilament-dependent processes for triggering lymphocyte activation.

The effects of Isoptin i) on isolated microtubules, ii) on the anti-immunoglobulin and the Concanavalin A induced changes in the plasma membrane topography of murine lymphocytes and iii) on murine lymphocyte activation by lipopolysaccharide and by Concanavalin A was investigated. Isoptin and lidocaine (a local anaestetic) inhibited repolymerisation of tubulin into microtubules and induced depolymerisation of microtubules. Isoptin and lidocaine inhibited competitively binding of colchicine (a classical microtubules disrupting agent) to tubulin. Isoptin induced changes in the plasma membrane topography resembling effects caused by local anaesthetics or by a combination of colchicine and cytochalasin B (an agent affecting microfilament function). Isoptin, lidocaine, colchicine and hydroxyurea when present in the culture medium during the whole incubation period inhibited DNA synthesis induced by lipopolysaccharide or Concanavalin A. RNA synthesis was completely inhibited by lidocaine but not by Isoptin or by colchicine. If Isoptin, colchicine or hydroxyurea were removed from the culture medium at 20 h of culture period, the cells immediately started to incorporate 3H-Thymidine. The inhibitory action of lidocaine was irreversible. These results show that Isoptin, a drug which depolymerizes microtubules in vitro and disturbs the mitogen induced changes in plasma membrane topography of lymphocytes (believed to be controlled by microtubules and microfilaments), does not abolish commitment of the cells for DNA synthesis.