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Microscopic and thermodynamic evaluation of vesicles shed by erythrocytes at elevated temperatures

Erythrocytes and vesicles shed by erythrocytes from human and rat blood were collected and analyzed after temperature was elevated by physical exercise or by exposure to external heat. The images of erythrocytes and vesicles were analyzed by the light microscopy system with spatial resolution of better than 90 nm. The samples were observed in an aqueous environment and required no freezing, dehydration, staining, shadowing, marking or any other manipulation. Temperature elevation, whether passive or through exercise, resulted in significant concentration increase of structurally transformed erythrocytes (echinocytes) and vesicles in blood. At temperature of 37 oC, mean vesicle concentrations and diameters in human and rat blood were (1.50+-0.35)x10^6 and (1.4+-0.2)x10^6 vesicles/μL, and 0.365+-0.065 and 0.436+-0.03 μm, respectively. It was estimated that 80% of all vesicles found in human blood are smaller than 0.4 μm. Thermodynamic analysis of experimental and literature data showed that erythrocyte transformation, vesicle release and other associated processes are driven by entropy with enthalpy-entropy compensation. It is suggested that physical state of hydrated cell membrane is responsible for the compensation. The increase of vesicle number related to elevated temperatures may be indicative of the heat stress level and serve as diagnostic of erythrocyte stability and human performance.