Effects of cellular morphology on the viscoelastic behavior of high hematocrit RBC suspensions

Abstract

Using a constant-amplitude (± 1°) oscillatory Couette viscometer (f=0.01–1.0 Hz), we have measured the viscous ( ${\mathit{\eta }}^{\prime }$ ) and elastic ( ${\mathit{\eta }}^{″}$ ) components of the complex viscosity at 25°C for shape-transformed human RBC suspended in isotonic buffer at 80% hematocrit. Morphology-altering drugs employed were: ECHINOCYTIC AGENT 2,4-dinitrophenol (DNP, 0.1–5 mM); STOMATOCYTIC AGENT chlorpromazine hydrochloride (CPZ, 0.01–0.1 mM). All suspensions exhibited decreasing ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ with increasing frequency. Compared to biconcave, control RBC suspensions, salient effects of shape transformation included: 1) for DNP, a dose-related elevation of both ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ , with a 850% increase in ${\mathit{\eta }}^{\prime }$ and a 2500% increase in ${\mathit{\eta }}^{″}$ at 5 mM and the lowest frequency; 2) for CPZ, a dose-related elevation of both ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ , with a 170% increase in ${\mathit{\eta }}^{\prime }$ and a 280% increase in ${\mathit{\eta }}^{″}$ at 0.1 mM and the lowest frequency; 3) for both DNP and CPZ, the elevations of ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ were inversely related to frequency. Using 2 mM DNP and various concentrations of CPZ, both ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ could be returned to control with 0.08 mM CPZ; further increases of CPZ at constant DNP led to elevations of both components. Comparisons of ${\mathit{\eta }}^{\prime }$ and ${\mathit{\eta }}^{″}$ to steady shear viscometric data indicated that neither a nominal shear rate approach nor a RMS complex viscosity technique was able to completely reconcile these data; a modified Kelvin-Voigt model proved useful in evaluating cellular versus membrane contributions to ${\mathit{\eta }}^{″}$ . These results indicate that RBC morphology is an important determinant of the oscillatory behavior of RBC suspensions and suggest the usefulness of the technique for studies of drug-membrane interactions.