Effect of Selective Alteration of Membranous or Cytoplasmic Properties on Erythrocyte Elongation in Shear Flow

Abstract

This study examines the relative contributions of the cytoplasmic and membranous compartments to the shear-induced elongation of single red blood cells (RBC). The mechanical properties of the cell membrane of normal human RBC were altered by controlled heat treatment (HT) (48°C for 1, 5 and 9 min). Using RBC transformed by conversion of intracellular hemoglobin to methemoglobin with nitrite as the oxidizing agent, a concomitant modification of cytosolic rheological properties was achieved by the same HT procedure. On exposure to heat, the viscosity of the methemoglobin solutions increased considerably. Cell elongation was measured in Dextran 60 suspensions sheared in a cone and plate rheoscope. Normal cells after 5 min of HT, and transformed cells after 1 min of HT yielded a two phase index of elongation curve which had a zero value within the lower shear rate range. Consequently, two indices of stiffening were introduced. One characterized the shear rate of transition from the zero value to the second inclined portion of the elongation curve. This index related to those cells that were oriented in the flow field but were not elongated. The other index characterized the maximum elongation at maximal shear rate in the rheoscope. In spite of the different kinematic states of cells described by the above two indices, identical rates of stiffening, as measured by the critical shear rate at which elongation sets in, or by the elongation parameter, with time of HT, were observed for normal and transformed cells. Further, transformed cells were stiffer than normal cells throughout the time of HT. These results may be explained by assuming that methemoglobin (MetHb) was bound to the endoface of the erythromembrane. The contribution of cytosolic dissipation of energy to cell elongation appears to be small.