Isoflurane alters proximal tubular cell susceptibility to toxic and hypoxic forms of attack.
BACKGROUND
Fluorinated anesthetics can profoundly alter plasma membrane structure and function, potentially impacting cell injury responses. Because major surgery often precipitates acute renal failure, this study assessed whether the most commonly used fluorinated anesthetic, isoflurane, alters tubular cell responses to toxic and hypoxic attack.


METHODS
Mouse proximal tubule segments were incubated under control conditions or with a clinically relevant isoflurane dose. Cell viability (lactate dehydrogenase release), deacylation (fatty acid, such as C20:4 levels), and adenosine triphosphate (ATP) concentrations were assessed under one or more of the following conditions: (a) exogenous phospholipase A2 (PLA2) or C20:4 addition, (b) Ca2+ overload (A23187 ionophore), (c) increased metabolic work (Na ionophore), and (d) hypoxia- or antimycin A-induced attack. Isoflurane's effect on NBD phosphatidylserine uptake (an index of plasma membrane aminophospholipid translocase activity) was also assessed.


RESULTS
Isoflurane alone caused trivial deacylation and no lactate dehydrogenase release. However, it strikingly sensitized to both PLA2- and A23187-induced deacylation and cell death. Isoflurane also exacerbated C20:4's direct membrane lytic effect. Under conditions of mild ATP depletion (Na ionophore-induced increased ATP consumption; PLA2-induced mitochondrial suppression), isoflurane provoked moderate/severe ATP reductions and cell death. Conversely, under conditions of maximal ATP depletion (hypoxia, antimycin), isoflurane conferred a modest cytoprotective effect. Isoflurane blocked aminophospholipid translocase activity, which normally maintains plasma membrane lipid asymmetry (that is, preventing its "flip flop").


CONCLUSIONS
Isoflurane profoundly and differentially affects tubular cell responses to toxic and hypoxic attack. Direct drug-induced alterations in lipid trafficking/plasma membrane orientation and in cell energy production are likely involved. Although the in vivo relevance of these findings remains unknown, they have potential implications for intraoperative renal tubular cell structure/function and how cells may respond to superimposed attack.
Zager
R A
RA
The Fred Hutchinson Cancer Research Center and the University of Washington, Seattle, Washington, USA. dzager@fhcrc.org
Burkhart
K M
KM
Conrad
D S
DS
D000255:Adenosine Triphosphate / Q000378:metabolism; D000666:Amphotericin B / Q000633:toxicity; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000633:toxicity; D000001:Calcimycin / Q000633:toxicity; D016923:Cell Death / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D006461:Hemolysis / Q000187:drug effects; D066298:In Vitro Techniques; D007476:Ionophores / Q000633:toxicity; D007530:Isoflurane / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000293:injuries / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D051379:Mice; D010741:Phospholipases A / Q000633:toxicity; D054467:Phospholipases A2
D018685:Anesthetics, Inhalation; D005230:Fatty Acids, Nonesterified; D007476:Ionophores; D016718:Arachidonic Acid; D000001:Calcimycin; D000666:Amphotericin B; D000255:Adenosine Triphosphate; D007530:Isoflurane; D007770:L-Lactate Dehydrogenase; D010741:Phospholipases A; D054467:Phospholipases A2