INTERACTION OF LOCAL AND GENERAL ANESTHETICS WITH PHOSPHATIDYLCHOLINE AND PHOSPHATIDYLGLYCEROL DISPERSIONS

The interaction of local and general anesthetics with phospholipids has been investigated using binary mixtures of phosphatidylcholine (PC) and phosphatidylglycerol (PG) as models for the axonal membrane. The effect of metal ions and anesthetics on the gel-to-liquid crystal thermal phase transition of the phospholipid mixtures was determined by differential scanning calorimetry. Divalent metal ions raised the transition temperature with Ca('+2) producing the greatest effect; Mn('+2) and Mg('+2) had only marginal effects. Ca('+2) caused lateral phase separation whereas Mg('+2) and Mn('+2) did not. Eu('+3) raised the transition temperature for mixtures containing less than 50% PG but depressed it for mixtures with more than 50% PG. Ester-type local anesthetics (benzocaine, chloroprocaine, tetracaine) caused the greatest depression of the phase transition temperature for mixtures containing 50% PG or less. Amide-type anesthetics (mepivacaine, bupivacaine, lidocaine, etidocaine) caused the greatest depression of the transition temperature for 100% PG samples. Halothane had a greater effect on membranes containing PG than for pure PC, but the amount of PG was not critical. There was no evidence for competition between metal ions and anesthetics for membrane binding sites. Partitioning experiments using C-14 labelled halothane showed that halothane was equally soluble in PC and PG, regardless of whether Ca('+2) was present. The fluorescent probe pyrene was used to examine the intramembrane distribution of halothane, which was different in lipid dispersions containing PG than for pure PC. Quenching was less efficient in the presence of Ca('+2) and Eu('+3).; A study using TNS as a dye binding probe of human and bovine prothrombin and fragment 1 in the presence and absence of Ca('+2) and Mg('+2) yielded data consistent with a model involving two crucial structural metal ion binding sites in prothrombin. TNS binding to the amino terminal region of prothrombin is shown to be a relatively simple probe of the relationship between protein structure and phospholipid binding.