Plasma membrane damage sensing and repairing. Role of heterotrimeric G-proteins and the cytoskeleton

Different toxic agents, derived from bacteria, viruses or cells of the immune system, as well as mechanical forces generated during cell locomotion are able to open pores in the cell plasma membrane. Most of these biological agents operate through specific receptors. We studied the formation and resealing of the "non-specific" plasma membrane pores generated by the mild non-ionic detergent Triton X-100. In HL-60-derived granulocytic cells plasma membrane pore opening after a 1-h treatment with Triton X-100 is documented by entry into the cell of the membrane impermeant dye ethidium bromide. As a consequence of the opening of pores the intracellular K(+) concentration falls dramatically, the cytosolic pH diminishes and the cell membrane is depolarized. Furthermore the cells acquire a polarized morphology, demonstrating the involvement of the actin cytoskeleton. At the Triton concentration used the membrane lesions are progressively repaired and by 8h the impermeability to ethidium bromide is restored and the intracellular K(+) concentration is virtually normal. Following treatments with Triton+Pertussis toxin, Triton+Cytochalasin, or Triton+Pertussis toxin+Cytochalasin the progress of membrane repair is dramatically slowed and is no longer completed by 8h. It is concluded that the membrane damage activates pertussis-sensitive G-proteins which likely act as sensors of the damage, while both G-proteins and the actin cytoskeleton are involved in the membrane repair mechanism.