Effects of energy limitation on Ca2+ and K+ homeostasis in anoxia-tolerant and anoxia-intolerant hepatocytes.
To gain more insight into the mechanistic basis of anoxia tolerance and intolerance, a comparative study was conducted on calcium homeostasis in goldfish and trout hepatocytes subjected to different forms of energy limitation. Using the fluorescent Ca2+ indicator fura 2, we observed that both chemical anoxia and true anoxia led to an increase of the concentration of cytosolic free calcium (Ca2+i) in the anoxia-sensitive hepatocytes of rainbow trout, whereas Ca2+i was maintained at control levels in the anoxia-tolerant hepatocytes of goldfish. Various lines of evidence suggest an intracellular origin of the Ca2+ increase observed in trout cells. Cyclosporin A, a specific inhibitor of the mitochondrial permeability transition pore in mammalian cells, was ineffective in preventing the Ca2+ increase, whereas a high dose of fructose depressed the Ca2+ surge by approximately 50%. The latter effect was not accompanied by improvement of the energetic state of the cells. A comparison of chemical anoxia with true (physiological) anoxia revealed that both treatments affected energy metabolism to a similar degree in trout hepatocytes, whereas the decrease of ATP seen in goldfish hepatocytes during chemical anoxia was absent during true anoxia. Elevation of Ca2+i with the calcium ionophore A-23187 led to a decoupling of unidirectional K+ fluxes in both normoxic and anoxic trout cells, whereas in goldfish hepatocytes the coupling of K+ fluxes was not affected by the rise of Ca2+i.
Krumschnabel
G
G
Abteilung für Okophysiologie, Universität Innsbruck, Austria.
Schwarzbaum
P J
PJ
Biasi
C
C
Dorigatti
M
M
Wieser
W
W
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D003530:Cyprinidae; D003600:Cytosol / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D016257:Fura-2; D006054:Goldfish; D006706:Homeostasis; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008322:Mammals; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D017686:Oncorhynchus mykiss; D011188:Potassium / Q000378:metabolism*; D012487:Salmonidae; D012966:Sodium Cyanide / Q000494:pharmacology; D013045:Species Specificity; D019284:Thapsigargin / Q000494:pharmacology
D007773:Lactates; D019284:Thapsigargin; D016572:Cyclosporine; D000255:Adenosine Triphosphate; D012966:Sodium Cyanide; D011188:Potassium; D002118:Calcium; D016257:Fura-2; D004837:Epinephrine