Spontaneous and forced oscillations of cell membrane of normal human erythrocytes: absence of resonance frequencies in a range of 0.03-500 Hz.

The spectra of natural oscillations of human erythrocyte cell membranes were studied experimentally and theoretically. The measurements were carried out at room temperature for both single normal cells and erythrocyte rouleaux in a range of 0.03-500 Hz. The spectra were measured at a resolution better than 1% using two techniques: registration of spontaneous membrane oscillations induced by thermal agitation in the surrounding medium and registration of the amplitude-frequency characteristics of the forced oscillations of erythrocyte elongation induced by a high-frequency electric field with the amplitude harmonic modulation. The spectra measured by both techniques had no resonance frequencies and decreased monotonically with the frequency increase. These results are confirmed by the theory developed for the extracellular excitation mechanisms of membrane oscillations. The spectra of active oscillatory biomechanical processes were measured for comparison. These processes are ciliary beating of human bronchial epithelium and ciliary beating and artificial periodic contractions of the cytoplasm of the ciliate Spirostomum ambiguum. The quality of the resonance lines of the order of 10-20 registered may serve as estimates for the line width in search of the resonance oscillations in erythrocytes induced by active cell processes.