Shinpei Ohki

Effect of local anesthetics on phospholipid bilayers

Abstract A study was made on the effect of four local anesthetics (nupercaine, tetracaine, cocaine and procaine) on d.c. resistance and the inhibition of Ca 2+ binding of various phospholipid membranes. When the local anesthetics were applied on one side of the membrane, the electrical resistance of phospholipid membrane decreased with the increase of the concentrations of the local anesthetics. On the other hand, when the local anesthetics were applied on both sides of the membrane, the membrane showed high resistance at low concentrations of the local anesthetics. Also, the instability of the acidic phospholipid asymmetric membrane due to Ca 2+ binding on one side of the membrane was inhibited by the presence of the local anesthetics in the solution. The potency of the lowering resistance of the membrane and the inhibition of instability of the asymmetric membrane with Ca 2+ binding by the local anesthetics was similar to earlier works (nupercaine > tetracaine > cocaine > procaine).

Stability of asymmetrical phospholipid bilayers

Abstract Instability of a phospholipid bilayer, which has an asymmetrical distribution with respect to Ca 2+ , pH and electric field in the solution, was investigated experimentally. It is deduced that the instability of the asymmetrical membrane is due to the difference in surface energy (surface potential) between the opposing sides of the phospholipid bilayer, and that the difference in ionization of one charge per molecule of the membrane between the two sides of the bilayer may produce the instability of the membrane. It was also observed that an acidic phospholipid membrane (phosphatidyl serine) becomes more unstable for the asymmetrical distribution with respect to the above environment than a neutral charged phospholipid membrane (phosphatidyl choline).

Asymmetric Phospholipid Membranes: Effect of pH and Ca2+

Phosphatidylserine membranes (either as liquid-crystalline vesicles or as bilayers) in 0.1M NaCl and neutral pH, are very impermeable to cations or anions and exhibit high electrical resistance (5 × 107 Ωcm2). However, the same membranes become unstable under conditions of asymmetric distribution of Ca2+ or H+: Addition of Ca2+ to the aqueous salt solution only on one side of the membrane, produces a lowering of the d. c. resistance, and above a certain concentration results in breakage of the membrane. On the other hand, if Ca2+ is present on both sides, the membranes are stable and show very high electrical resistance (5 × 108Ωcm2) over a wide pH range. The above phenomena were not observed with membranes made of phosphatidylcholine. It is suggested that the instability of PS membranes observed in this study is due to the difference in surface energy between the two opposing sides of the bilayer. The biological implications of membrane instability following an asymmetric distribution of Ca2+ or H+ is discussed.

806—Membrane potential of squid axons: Comparison between the Goldman-Hodgkin-Kantz equation and the surface/diffusion potential equation☆

Abstract The resting membrane potential of squid axons measured as a function of the nature of the ionic species as well as the ionic strength of the extracellular medium. The observed membrane potentials were analyzed using two equations: 1. the Goldman-Hodgkin-Katz equation, and 2. the surface/diffusion potential equation, using the same relative permeability factors. The overall experimental results were found to be explained better by the surface/diffusion potential equation. The surface charge density of the outer surface (on the responsible for the iron transfer) of the squid axons was found to be about - e /180 A 2 . Using the obtained surface charge density and the membrane potential equation involving divalent cations, the relative permeabilities (with respect to K + ) of divalent cations across the squid axon membranes were observed to be 0.035 for Ca 2+ , 0.033 for Sr 2+ and 0.023 for Mg 2+ fron the experimental data.