Role of intracellular signaling systems in regulation of erythrocyte microrheology

Abstract

Erythrocyte deformability and thus the efficiency of the oxygen delivery to tissues depends on three main factors: elasticity of cell membrane, viscosity of cytoplasm, and the erythrocyte surface/volume ratio. The membrane elasticity and stability most considerably contribute to the whole cell deformability. There are experimental data suggesting that erythrocyte deformability is regulated by intracellular signaling pathways. The aim of this work was to study the role of the adenylyl cyclase–cAMP systems and intracellular calcium signaling mechanism in the regulation of erythrocyte deformability. We found that stimulator of adenylyl cyclase (AC) forskolin (10–5 M) and cell-penetrating cAMP analog dB-cAMP (5 × 10–5 M) increased erythrocyte deformability. Inhibitors of the phosphodiesterase (PDE) activity, such as isobutyl methylxanthine, vinpocetine, and cilostazol (10–5 M), also increased the erythrocyte deformability, which provides another line of evidence of the cAMP involvement in the regulation of erythrocyte deformability. On the other hand, stimulation of Ca2+ entry into erythrocytes induced by Ca2+ ionophore A23187 (3 × 10–6 M), sodium fluoride, or sodium vanadate considerably decreased the cell deformability, while blockade of the Ca2+ entry into erythrocytes by verapamil (10–5 M) increased their deformability. Mechanical stress of the erythrocyte membrane in the absence of extracellular Ca2+ did not change the deformability, while the mechanical stress applied in the presence of Ca2+ (50–200 µM) decreased deformability by 4–18%. On the whole, the obtained results suggest that for the increase in the erythrocyte deformability the AC–cAMP–PKA cascade has to be activated, while the pathway triggered by the Ca2+ entry into the cells is required to lower the erythrocyte deformability (elasticity) and hence, to increase the whole cell membrane stability. It is possible that these pathways are coordinated at the PDE level.