Effects of halothane on the incorporation of [14C]-serine into phospholipid in the guinea-pig ileum.

1 The effects of halothane on the incorporation of L-[3-14C]-serine into phospholipid were studied in the resting, innervated longitudinal muscle preparation of the guinea-pig ileum. 2 The anaesthetic, at clinical concentrations, caused a dose-dependent, partial inhibition of incorporation. The effect was rapid and reversible, and did not show characteristics of competitive inhibition. 3 The incorporation was reduced by a decrease in the Ca2+ concentration of the Krebs incubation buffer. Part of the activity persisted in the absence of added Ca2+ and this was most susceptible to inhibition by halothane. Sensitivity to external Ca2+ was not influenced at the halothane concentrations studied. 4 Evidence in support of the 14C-incorporation being due to L-[3-14C]-serine-phospholipid base-exchange activity included: (a) the rapid appearance of radioactivity in phosphatidylserine; (b) the kinetics of this incorporation in relation to that in phosphatidylethanolamine; (c) its dependence on Ca2+, and (d) its sensitivity to 2,4-dinitrophenol and its sensitivity to temperature. 5 It is concluded that this preparation makes it possible for a membrane-bound lipid-dependent activity (L-serine-phospholipid base-exchange) to be studied in conditions of cellular integrity under which the normal functional effects of lipophilic drugs can be simultaneously tested. 6 A rapid gas-chromatographic assay for halothane from an aqueous medium is also described.