A dilatometric investigation of the effects of general anaesthetics,alcohols and hydrostatic pressure on the phase transition in smectic mesophases of dipalmitoyl phosphatidylcholine |
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Authors: | AG Macdonald |
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Institution: | Physiology Department, University of Aberdeen, Aberdeen AB9 1AS U.K. |
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Abstract: | The effect of general anaesthetics, alcohols and hydrostatic pressure on the thermal transition in dipalmitoyl phosphatidylcholine multilayer liposomes has been measured using dilatometry. The volume increasse at the transition (ΔVt) is 0.0350 ± 0.0003 ml/g. the transition temperature (Tt) 41.84 ± 0.09°C and the width of the transition 1.025 ± 0.18°C. ΔH calculated by the Clapeyron-Clausius equation is 8.4 kcal/mol. The n-alcohols C3C5 reduced the transition temperature without affecting the transition width which was however, increased by n-hexanol. Trichloroethylene, the fluorescent probe N-phenyl-1-naphthyl-amine, and methoxyflurane all increased the transition width (reduced the cooperativity of the transition) with a simultaneous depression of Tt. Methoxyflurane caused a two-stage transition expansion. Diethyl ether's effect has similarities with both the C3 and C6 alcohols. Generally ΔVt was unaffected by the agents.Pressure increased Tt by 0.0238°C/atm linearly over the range 1–300 atm in both treated and untreated liposomes, and therefore cannot be said to antagonize anaesthetics. In both treated and untreated liposomes ΔVt and the width of the transition were unaffected by pressure. Pressure thus reverses the effects of anaesthetics on Tt but not their spread of the transition width. |
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