Halothane increases cytosolic Ca2+ and inhibits Na+/H+ exchange in L6 muscle cells.
The effects of the general anesthetic halothane on the concentration of cytosolic free calcium ([Ca2+]i) and cytosolic pH (pHi), were investigated in L6 rat skeletal muscle cells. Basal [Ca2+]i was 169 +/- 8 nM, measured with the fluorescent Ca2(+)-indicator 1-[2-amino-5-(6-carboxyindol-2-yl)phenoxy]-2-(2'-amino-5- methylphenoxy)ethane-N,N,N',N'-tetra-acetate. Halothane (5.7 mM) increased [Ca2+]i to 225 +/- 15 nM in the presence of extracellular Ca2+, and from 137 +/- 6 nM to 179 +/- 9 nM in Ca2+ absence. This increase was dose-dependent. The anesthetic released about 50% of the releasable Ca2+ from intracellular stores. The resting pHi of L6 cells was 7.24 +/- 0.04, measured with the fluorescent pH indicator bis-carboxyethylcarboxyfluorescein. Halothane did not affect resting pHi, but inhibited cytoplasmic alkalinization by hypertonicity or cytoplasmic acidification: (1) The hypertonicity-induced alkalinization via activation of Na+/H+ exchange (to 7.50 +/- 0.08, initial rate 0.10 +/- 0.02 pH U/min) was inhibited with 5.7 mM halothane by 67%. (2) Acid-loaded cells (pHi 6.43 +/- 0.01 in cells) recovered towards neutrality via activation of Na+/H+ exchange (rate 0.47 pH U/min), and halothane inhibited the rate of pHi recovery by 50%. The halothane-mediated inhibition of alkalinizations after hypertonic exposure or acid-loading was also observed in bis-(o-amino-phenoxy)ethane-N,N,N',N'-tetra-acetate-loaded cells in Ca2(+)-free medium. Therefore, halothane increases [Ca2+]i and in parallel inhibits Na+/H+ exchange, compromising the ability of muscle cells to recover from imposed acidification.
Klip
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Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Hill
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Ramlal
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D006221:Halothane / Q000494:pharmacology*; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D015759:Ionomycin / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism*
D015759:Ionomycin; D006859:Hydrogen; D012964:Sodium; D002118:Calcium; D006221:Halothane