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Notes: Summary The electric capacitance and conductance of a model membrane composed of a hydrophobic filter paper and a synthetic lipid analogue, i.e., dioleylphosphate, immersed in an electrolyte solution were observed with various frequencies ranging from 20 to 3×106 Hz. With successive increase of salt concentration in the external solution, the capacitance and conductance of the membrane increased discontinuously at a certain critical value of the external salt concentration. This variation of the capacitance and conductance of the membrane with the salt concentration was found to be reversible, and the critical value of salt concentration was independent of the adsorbed quantity of the lipid, and of the pore size of the filter paper as far as the adsorbed quantity of the dioleylphosphate was large. A theoretical analysis based on the membrane model for the filter paper-phospholipid system proposed in Part I of this series revealed that the dioleylphosphate impregnated in the filter paper changed its conformation from oil droplets or globular micelles to a number of bilayer membranes when the salt concentration reached the critical value for a given pair of electrolyte species and the membrane. The conformational change of the lipid analogue in the filter paper is discussed in connection with the ability of formation and stability of a black bilayer membrane of the dioleylphosphate.

Notes: Summary The protoplasmic drop isolated fromNitella became electrically excitable in an appropriate salt solution. Variations of salt composition and temperature in the external media induced discrete changes in the interfacial properties such as refractive index or surface tension, as well as in the electrical properties of the protoplasmic drop. Variation of salt composition was performed by changing the concentration of the respective component at a time from the original test solution (0.5mm NaCl, 0.5mm KNO3, 1mm Ca(NO3)2, and 2mm Mg(NO3)2) with other components being fixed. The following results were obtained: (1) An increase of concentration of univalent cation (Na+ or K+) induced a sharp rise of the refractive index from 1.42 to 1.58 at about 10mm, which was accompanied by a discrete depolarization of the membrane potential of the drop. Fluctuation of reflected light was observed at the critical concentration. (2) The refractive index remained at low values of about 1.42 in Ca2+ concentration ranging between about 0.1 and 10mm. Beyond this concentration range of Ca2+, i.e., both lower and higher, the refractive index increased discontinuously to the value of about 1.58. (3) An addition of multi-valued cations in the test solution led to an abrupt depolarization of the membrane potential at a definite concentration for each ion species. The critical salt concentration dependent strongly on thevalence of cations added, and gave the following series: Th4+〈La3+〈Ba2+, Sr2+〈Na+. (4) Lowering of the surrounding temperature induced an abrupt depolarization of the membrane potential when the Ca2+ concentration in the external solution was close to the lower critical concentration, i.e. 0.1mm. (5) A rise in temperature led to an increase of fluctuations of the membrane potential with frequent outbreaks of small spike potentials, which were followed by an abrupt depolarization. At the same time the tension at the surface decreased discontinuously from 10−1 dynes/cm to the order of 10−4 dynes/cm. All these changes were reversible. These results imply that the surface membrane of the protoplasmic drop is liable to change its structure in response to the variation of temperature, salt composition in the external media and/or electrical stimulus. Drastic variations of membrane properties such as surface tension, membrane potential and membrane resistance are discussed in connection with the structural change determined by the refractive index measurements.

Notes: Summary Membrane potential Δϕ m ion permeabilityP and d-c conductanceG p 0 of a model membrane composed of a filter paper and a synthetic lipid analogue, i.e. dioleylphosphate (DOPH), were observed in various concentrations of 1∶1 type electrolyte solution. With successive increases of salt concentration in the external solution, Δϕ m ,P andG p 0 changed their values rather discontinuously at a certain critical value of the concentrationc t . When the concentration was decreased successively, the values of Δϕ m ,P andG p 0 were returned to the original levels at a concentration much lower thanc t . Thus, the transport phenomena observed across the membrane showed an appreciable hysteresis loop. The discontinuous variations of Δϕ m ,P andG p 0 were interpreted in terms of a transition of DOPH adsorbed in the filter paper from an oil membrane to a charged membrane. This transformation of DOPH at the critical salt concentration is consistent with the previous argument that the DOPH impregnated in the filter paper changes its conformation from oil droplets to a number of bilayer films, which deduced from a theoretical analysis of frequency dependency of the electrical capacitance of the membrane.