Ca2+ antagonists do not protect isolated perfused rat hepatocytes from anoxic injury.
Ca2+ antagonists were studied during anoxia in perfused isolated rat hepatocytes. Cytosolic free calcium (Ca2+i) was measured with aequorin. Anoxia was induced for 2 h by saturating the perfusate with 95% N2/5+ CO2. Anoxia increased Ca2+i in two distinct phases reaching a maximum of 1.5 microM. The increase in Ca2+i was caused by Ca2+ influx from the extracellular fluids because the main Ca2+i surge was totally abolished in Ca(2+)-free media. LDH release increased 6-fold during the second hour of anoxia, but when Ca2+ was removed from the perfusate during the anoxic period, LDH rose only 2.7-fold. Ca2+ antagonists (10(-7) to 10(-5) M) did not prevent the increase in Ca2+i and the rise in LDH release. On the contrary, high concentrations (10(-6) and 10(-5) M) of the blockers nifedipine and diltiazem significantly increased anoxic cell injury. The observation that the increase in LDH and the rise in Ca2+i were not suppressed by Ca2+ antagonists suggests that (i) Ca2+ antagonists protect the whole liver from anoxic injury by acting on cells other than parenchymal cells; (ii) the influx of Ca2+ responsible for the massive increase in hepatocyte Ca2+i evoked by anoxia did not take place through voltage-sensitive Ca2+ channels but must have occurred via the Na(+)-Ca2+ antiporter operating in the reverse mode (Ca2+ influx vs. Na+ efflux), and (iii) high concentrations of Ca2+ antagonists may be deleterious to the parenchymal cells of the liver.
Gasbarrini
A
A
Department of Physiology, University of Pittsburgh School of Medicine, PA 15261.
Borle
A B
AB
Van Thiel
D H
DH
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015687:Cell Hypoxia / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D014343:Trypan Blue / Q000378:metabolism
D002121:Calcium Channel Blockers; D007770:L-Lactate Dehydrogenase; D014343:Trypan Blue; D002118:Calcium