Molecular pharmacology
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Molecular pharmacology · Jan 1984
Membrane expansion and inhalation anesthetics. Mean excess volume hypothesis.
High-precision solution densimetry was used to determine volume parameters for the interaction of inhalation anesthetics with water, nonpolar solvent, and phospholipid vesicles. The precision of the densimeter is mainly limited by the constancy of the temperature during measurement. Therefore, temperature stability was maintained within +/- 0.0005 degrees and monitored by a microprocessor-controlled Thermistor thermometer with 0.0001 degrees resolution. ⋯ Because the mean excess volume of anesthetics dissolved in water is always negative and that incorporated into phospholipid suspension is positive, anesthetics expand the total volume of the model membrane system when translocated from water to the membrane. Anesthesia occurs when the mean excess volume of the total system exceeds a limiting value, and the bulk membrane size is irrelevant. Although the present result in no way disclaims alternative hypotheses, it demonstrates that the pressure reversal of anesthesia can be explained without assuming any specific receptors for these anesthetics.