Repolarization of the membrane potential of blood platelets after complement damage: evidence for a Ca++ -dependent exocytotic elimination of C5b-9 pores.
Gel-filtered blood platelets exposed to complement proteins C5b-9 have previously been shown to undergo a reversible depolarization of membrane potential (Em) in the absence of lytic plasma membrane rupture. In this paper, we examine the mechanism by which C5b-9 damaged platelets restore their basal electrochemical state, despite increased ion conductance due to membrane insertion of these cytolytic serum proteins. Repolarization of Em after formation of the C5b-9 membrane pore is shown to be accompanied by a Ca++-dependent vesiculation of the platelet surface, which results in the release of these proteins from the plasma membrane and a restoration of the membrane's functional integrity. This exocytotic elimination of C5b-9 complexes from the plasma membrane is accompanied by a ouabain-inhibitable repolarization of Em, which presumably reflects restoration of transmembrane cation gradients by the plasma membrane Na/K ATPase. The role of external Ca++ in the platelet's response to membrane-insertion of the C5b-9 proteins is discussed both in the context of the known cellular effects of this ion and in the context of recent observations suggesting sublytic changes in platelet function after complement-mediated plasma membrane damage.
D000328:Adult; D001792:Blood Platelets / Q000166:cytology* / Q000502:physiology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000502:physiology; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000502:physiology*; D006801:Humans; D008564:Membrane Potentials; D008855:Microscopy, Electron, Scanning; D009504:Neutrophils / Q000502:physiology
D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins; D002118:Calcium