Viscous flow of cytoplasm and red cell membrane: membrane recovery and tether contraction

Several experiments have been designed to study the flow of membrane and measure its viscosity. In all cases, the viscous dissipation in the cytoplasm (i.e., hemoglobin) is assumed to be negligible in comparison to that in the membrane although this has not been shown analytically. Therefore, we analyze here the viscous flow or "dissipation" in membrane and hemoglobin for two particular experiments. One involves the recovery within a pipet of an aspirated portion of a membrane following the release of the aspiration pressure; the other involves the contraction of a membrane cylinder (tether) following a step change in the axial force acting on the tether. For the pipet -recovery experiment, our results indicate that the viscosity of hemoglobin must be 100 times larger before its dissipation compares to that in the membrane. For the tether-contraction experiment, hemoglobin viscosity must be 1000 to 10,000 times larger before it is significant. A preliminary result from a tether-contraction experiment gives a characteristic response time (approximately 10 sec) and a viscosity (approximately 10(-3) dyn X sec/cm) consistent with the analytical result that hemoglobin dissipation is negligible.