Mechanism of Erythrocyte Deformation under the Action of Stress Hormones

Optical methods (interferometry, UV, FTIR and IR spectroscopy) were used to study erythrocyte deformation occurring under the action of adrenaline and cortisol. These hormones give rise to mechanical stresses (contraction) on erythrocytes ghosts, which show up as an increased structural orderliness of membrane proteins, in particular, of the protein domains belonging to contraction and integral proteins. An increasing orderliness of protein domains is accompanied by splitting the absorption band of NH peptide bond (stretching vibrations). In this case, changes of domain orderliness occur mainly in contraction proteins due to their high concentration with respect to other membrane proteins. In addition, adrenaline β-structure and raise the intensity of absorption bands at 1630, 1686 or 1696 cm –1 . Cortisol increase the fraction of α-helices. Finally, along with alteration of the protein structure, we observed an increase of phospholipid orderliness in domains and that of interdomain orderliness, which show up as splitting of absorption bands of the stretching and deformation vibrations of CH bonds as well as Р=О and POC bonds. The effects produced by the hormones in erythrocyte ghosts are shown to persist on intact erythrocytes. FTIR spectroscopy study using the Frustrated Total Internal Reflection method revealed splitting of absorption bands of the stretching vibrations of NH, СH and РО 2 bonds and an increase in the fraction of β-structure and α- helices. We found also the hypochromic effect of absorption band at 418 nm (UV spectrometer), which corresponds to the band of heme. The hypochromic effect of this band is caused by increasing orderliness of hemoglobin and heme, it indicates a growing affinity for oxygen. Thus, stress hormones alter the oxygen transport properties of erythrocytes. Besides, interferometry allowed us to observe an abrupt change of refraction factor, and UV spectroscopy detected a non-monotonic increase of light diffusion in erythrocyte suspensions with the hormones. These data reflect the deformation of erythrocytes under the action of hormones. In our opinion, a possible mechanism of structural transitions in hemoglobin produced by stress hormones may be related with changes in elastic free energy of a cell and subsequent changes in osmotic, oncotic and hydrodynamic pressure. Changes in elastic free energy of a cell are caused mainly by the contraction network. Deformation of erythrocytes under the action of stress hormones occurs as adiabatic process. Taking into account the structural transitions in erythrocytes under the influence of adrenaline we might suggest that the change of β-structure (α-helix→β-structure transition) occurs to adrenoreceptor at first spreads to the contractile net-in whole, that leads to generalized transition in membrane and cell.