Stimulation of erythrocyte phosphatidylserine exposure by lead ions.
Pb+ intoxication causes anemia that is partially due to a decreased life span of circulating erythrocytes. As shown recently, a Ca(2+)-sensitive erythrocyte scramblase is activated by osmotic shock, oxidative stress, and/or energy depletion, leading to exposure of phosphatidylserine at the erythrocyte surface. Because macrophages are equipped with phosphatidylserine receptors, they bind, engulf, and degrade phosphatidylserine-exposing cells. The present experiments were performed to explore whether Pb+ ions trigger phosphatidylserine exposure of erythrocytes. The phosphatidylserine exposure was estimated on the basis of annexin binding as determined using fluorescence-activated cell sorting (FACS) analysis. Exposure to Pb+ ions [> or =0.1 microM Pb(NO3)2] significantly increased annexin binding. This effect was paralleled by erythrocyte shrinkage, which was apparent on the basis of the decrease in forward scatter in FACS analysis. The effect of Pb+ ions on cell volume was virtually abolished, and the effect of Pb+ ions on annexin binding was blunted after increase of extracellular K+ concentration. Moreover, both effects of Pb+ ions were partially prevented in the presence of clotrimazole (10 microM), an inhibitor of the Ca(2+)-sensitive K+ channels in the erythrocyte cell membrane. Whole cell patch-clamp experiments disclosed a significant activation of a K(+)-selective conductance after Pb+ ion exposure, an effect requiring higher (10 microM) concentrations, however. In conclusion, Pb+ ions activate erythrocyte K+ channels, leading to erythrocyte shrinkage, and also activate the erythrocyte scramblase, leading to phosphatidylserine exposure. The effect could well contribute to the reported decreased life span of circulating erythrocytes during Pb+ intoxication.
Kempe
Daniela S
DS
Department of Physiology, University of Tübingen, Tübingen, Germany.
Lang
Philipp A
PA
Eisele
Kerstin
K
Klarl
Barbara A
BA
Wieder
Thomas
T
Huber
Stephan M
SM
Duranton
Christophe
C
Lang
Florian
F
D017302:Annexins / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D003022:Clotrimazole / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects* / Q000473:pathology; D005434:Flow Cytometry; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D007854:Lead / Q000633:toxicity*; D018408:Patch-Clamp Techniques; D010718:Phosphatidylserines / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism
D017302:Annexins; D006131:Growth Inhibitors; D010718:Phosphatidylserines; D015221:Potassium Channels; D007854:Lead; D003022:Clotrimazole; D002118:Calcium