Measurements of Ultrasonic Velocity of Erythrocyte Ghosts in Suspension with Sing-Around Method

Abstract

An apparatus utilizing a sing-around method was constructed consisting of a pulse generator, a sample holder with transducers and a Schmitt circuit, in which ultrasonic velocity was determined from the period of pulses by an electronic counter with a relative accuracy of 10-6. The velocity V and the denisty ρ were measured for suspensions of bovine erythrocyte ghosts in 150 mM NaCl at pH 7.0 as the temperature was varied from 20° to 40°C and the concentration c was varied from 1 to 8 mg in weights of dry membrane per 1 cm3. An abrupt change was observed in V and p between 31° and 33°C, which was considered as a transition from a crystalline to liquid-like structure in lipid hydrocarbon chains of the membrane. The density and the bulk modulus of the membrane were estimated from the limiting numbers of the density [ρ] and the velocity [V], where \\displaystyle[ρ] = lim c →0 (ρ-ρ0)/ρ0c , \\displaystyle[V] = lim c →0 (V-V0)/V0c and the subscript 0 denotes the medium.