Alterations of hepatocyte Ca2+ homeostasis by triethylated lead (Et3Pb+): are they correlated with cytotoxicity?
Isolated rat hepatocytes were used to investigate the biochemical mechanisms of toxicity of triethyllead (Et3Pb+), a highly neurotoxic degradation product of the antiknocking petrol additive tetraethyllead. As early as 5 min from the addition of 50 microM Et3Pb+ to hepatocyte suspensions a decrease of mitochondrial membrane potential and of the capacity of mitochondria and microsomes to retain Ca2+ occurred. A dose-dependent release of mitochondrial Ca2+ as well as an inhibition of microsomal Ca(2+)-ATPase activity were also evident when Et3Pb+ (from 2.5 microM up to 50 microM) was added to, respectively, isolated liver mitochondria and microsomes. Further experiments using hepatocytes loaded with the Ca2+ indicator Fura-2AM demonstrate that 1 min from addition of Et3Pb+ the cytosolic free Ca2+ levels increased by about 3-fold. High affinity plasma membrane Ca(2+)-ATPase activity was also significantly inhibited in hepatocytes treated with Et3Pb+, suggesting that an impairement of the mechanisms controlling the efflux of extracellular Ca2+ was concomitantly involved in the rise in cytosolic Ca2+ concentration. The increase in the cytosolic Ca2+ levels caused by Et3Pb+ was followed by a rapid decline of cell viability. However, the addition of EGTA or of the intracellular Ca2+ chelator BAPTA/AM did not affect either the time-course or the extent of cytotoxicity. Conversely, fructose, a glycolytic substrate that was able to support ATP production, prevented hepatocyte death. Thus, the depletion of cellular energy stores rather than the increase in cytosolic Ca2+ appears to be the mechanism by which Et3Pb+ causes irreversible injury in isolated hepatocytes.
Albano
E
E
Department of Medical Sciences, University of Torino, Novara, Italy.
Bellomo
G
G
Benedetti
A
A
Carini
R
R
Fulceri
R
R
Gamberucci
A
A
Parola
M
M
Comporti
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D066298:In Vitro Techniques; D007854:Lead / Q000494:pharmacology* / Q000633:toxicity; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects; D009942:Organometallic Compounds / Q000494:pharmacology* / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar
D009942:Organometallic Compounds; D007854:Lead; C010360:triethyllead; D000252:Calcium-Transporting ATPases; D002118:Calcium