FLUCTUATIONS OF THE RED BLOOD CELL MEMBRANE: RELATION TO MECHANICAL PROPERTIES AND LACK OF ATP-DEPENDENCE

¹ King's College London; New York Blood Center
² King's College London
³ New York Blood Center
⁴ Imperial College
⁵ King's College

^* To whom correspondence should be addressed. E-mail: john.sleep{at}kcl.ac.uk.

Submitted on July 24, 2007
Revised on September 3, 2007
Accepted on 2 January 2008

	Abstract

We have analysed the fluctuations of the red blood cell membrane in both the temporal (( (s^-1)) and spatial (q (m^-1)) frequency domains. The cells were examined over a range of osmolarities leading to cell volumes from 50% to 170% of that in the isotonic state. The fluctuations of the isotonic cell showed a ~q^-3-dependence, indicative of a motion dominated by bending, with an inferred bending modulus of about 9x10^-19J. When the cells were osmotically swollen to just below the point of lysis (166% of physiological volume), a q^-1-dependence of the fluctuations supervened, implying that the motion was now dominated by membrane tension; estimated as about 1.3x10^-4 Nm^-1. When, on the other hand, the cells were osmotically dehydrated, the fluctuation amplitude progressively decreased. This was caused by a rise in internal viscosity, as shown by measurements on resealed ghosts containing a reduced haemoglobin concentration, which displayed no such effect. We examined, in addition, cells depleted of ATP, before the onset of echinocytosis, and could observe no change in fluctuation amplitude. We conclude that the membrane fluctuations of the red cell are governed by bending modulus, membrane tension and cytosolic viscosity, with little or no dependence on the presence or absence of ATP.

Key Words: bending modulus, erythrocyte, fluctuation, sheer modulus