Heat capacity profiles of artificial unilamellar DPPC vesicles, bovine lung surfactant extract, E. coli membranes, and B. subtilis membranes. Transition peaks associated with protein unfolding are shaded in gray. The dotted line indicates T = 37°C, which is the bovine body temperature and the growth temperature of E. coli and B. subtilis.

Thermodynamic data for DPPC vesicles and lung surfactant. (Left) Heat capacity of DPPC large unilamellar vesicle (Top), lateral area density, ρ^A (Middle), and the corresponding lateral compressibility (Bottom) (isothermal area compressibility, solid curve, corresponding to a low-frequency case and adiabatic area compressibility, dotted line, corresponding to a 5-MHz ultrasonic experiment), as calculated from the heat capacity. (Center) The lateral sound velocity c² = 1/κ_SAρA [m²/s²] for the low-frequency and the 5-MHz case, as a function of membrane area density, ρ_A [g/m²]at T = 45°C. (Right) c² profiles for lung surfactant at T = 37°C calculated from the heat capacity in .

Soliton profiles. (Left) Soliton profiles for the DPPC large unilamellar vesicle membrane at T = 45°C obtained for velocities between v = 0.48 and 0.8 c₀. Larger profiles correspond to smaller velocities. The largest profile is essentially the limiting soliton. (Right) Soliton profiles for lung surfactant at T = 37°C obtained for velocities between v = 0.83 and 0.95 c₀. The maximum amplitude of the limiting soliton is very close to that found for the DPPC membrane.

Properties of solitons and nerves. (a) Calculated total energy and capacitive energy densities stored in the soliton during the passage. Both functions display similar time dependence. (b) Experimental heat changes during the action potential of garfish olfactory nerve (solid line) and the energy of charging the membrane's capacitor. Both functions display similar time dependence (adapted from ref. ). (c) Calculated thickness change of a membrane cylinder (displacement) and corresponding voltage changes. Both functions display identical time dependence. (d) Experimentally determined differential displacement of the squid axon and the corresponding action potential (adapted from ref. ). Both functions display identical time dependence. The different shape of the profiles as compared with b are a consequence of the experimental setup.