title: Effects of divalent cations on lipid flip-flop in the human erythrocyte membrane.
abstract: Treatment of human erythrocytes with ionophore A23187 (10 mumol.l-1) and Ca2+ (0.05-0.5 mmol.l-1) or Sr2+ (0.2-1 mmol.l-1) in results in a concentration-dependent acceleration of the transmembrane reorientation (flip) of the lipid probes lysophosphatidylcholine and palmitoylcarnitine to the inner membrane leaflet after their primary insertion into the outer leaflet. Mg2+, Mn2+, Zn2+ and La3+ do not accelerate flip. Ca2(+)-induced flip acceleration depends also on the ionophore concentration. It is reversed by removal of Ca2+ with EDTA. A causal role of Ca2(+)-induced membrane protein degradation and decrease of the polyphosphoinositide level in flip acceleration could be excluded. Likewise, calmodulin-dependent processes are probably not involved since the calmodulin antagonist calmidazolium (2-10 mumol.l-1) does not suppress but even enhances the Ca2(+)-induced flip acceleration. The same is true for the Ca2+ antagonist flunarizine. These drugs do not alter flip rate in the absence of Ca2+. At high Ca2+ (1-5 mmol.l-1) an initial flip acceleration is followed by flip normalization. High concentrations of Mn2+ and Mg2+ slow down flip rates. The selective acceleration of flip by Ca2+ and Sr2+ is discussed to be due to a local detachment of the membrane skeleton from the bilayer, whereas the unselective slow down of flip by divalent cations might be due to a stabilization of the membrane bilayer by the cations. After loading of cells with Ca2+ (but not with Mn2+) the inner membrane leaflet phospholipid phosphatidylserine becomes rapidly exposed to the outer membrane surface, as detectable by its accessibility to phospholipase A2 (5 min).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institut für Physiologie, Medizinische Fakultät, RWTH Aachen, F.R.G.
authors.forename: U
authors.initials: U
authors.lastname: Henseleit
authors.forename: G
authors.initials: G
authors.lastname: Plasa
authors.forename: C
authors.initials: C
authors.lastname: Haest
mesh_terms: D001692:Biological Transport; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000494:pharmacology; D002413:Cations, Divalent / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000378:metabolism*; D005444:Flunarizine / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D007093:Imidazoles; D008051:Lipid Bilayers; D010743:Phospholipids; D000001:Calcimycin; C031938:calmidazolium; D002154:Calpain; D005444:Flunarizine; D002118:Calcium