Stimulation of erythrocyte phosphatidylserine exposure by mercury ions.
The sequelae of mercury intoxication include induction of apoptosis. In nucleated cells, Hg2+-induced apoptosis involves mitochondrial damage. The present study has been performed to elucidate effects of Hg2+ in erythrocytes which lack mitochondria but are able to undergo apoptosis-like alterations of the cell membrane. Previous studies have documented that activation of a Ca2+-sensitive erythrocyte scramblase leads to exposure of phosphatidylserine at the erythrocyte surface, a typical feature of apoptotic cells. The erythrocyte scramblase is activated by osmotic shock, oxidative stress and/or energy depletion which increase cytosolic Ca2+ activity and/or activate a sphingomyelinase leading to formation of ceramide. Ceramide sensitizes the scramblase to Ca2+. The present experiments explored the effect of Hg2+ ions on erythrocytes. Phosphatidylserine exposure after mercury treatment was estimated from annexin binding as determined in FACS analysis. Exposure to Hg2+ (1 microM) indeed significantly increased annexin binding from 2.3+/-0.5% (control condition) to 23+/-6% (n=6). This effect was paralleled by activation of a clotrimazole-sensitive K+-selective conductance as measured by patch-clamp recordings and by transient cell shrinkage. Further experiments revealed also an increase of ceramide formation by approximately 66% (n=7) after challenge with mercury (1 microM). In conclusion, mercury ions activate a clotrimazole-sensitive K+-selective conductance leading to transient cell shrinkage. Moreover, Hg2+ increases ceramide formation. The observed mechanisms could similarly participate in the triggering of apoptosis in nucleated cells by Hg2+.
Eisele
Kerstin
K
Department of Physiology, University of Tübingen, Germany.
Lang
Philipp A
PA
Kempe
Daniela S
DS
Klarl
Barbara A
BA
Niemöller
Olivier
O
Wieder
Thomas
T
Huber
Stephan M
SM
Duranton
Christophe
C
Lang
Florian
F
D017302:Annexins / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism; D003022:Clotrimazole / Q000494:pharmacology; D004906:Erythrocyte Count; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D008627:Mercuric Chloride / Q000633:toxicity*; D018408:Patch-Clamp Techniques; D010718:Phosphatidylserines / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism
D017302:Annexins; D002518:Ceramides; D010718:Phosphatidylserines; D015221:Potassium Channels; D008627:Mercuric Chloride; D003022:Clotrimazole; D002118:Calcium