Effects of various osmolarity on human red blood cells in terms of potassium efflux and hemolysis induced by free radicals.

Objectives: To study in an in vitro model of erythrocytes exposed to free radicals the effects of hyperosmolarity and hypoosmolarity on the induced potassium efflux and hemolysis.

Design Setting: Erythrocytes were separated from plasma and suspended in 3 different phosphate buffer solutions (HYPO, ISO, and HYPER) containing, respectively, 100, 150 and 200 mmol/l of Na. Free radicals were generated from 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH). Potassium efflux (flame photometry) and hemolysis (Drabkin method) were measured. Measurements were expressed in % (versus total) and area under % versus time curves were calculated (% min). An ANOVA was used for statistical analysis.

Results: In presence of AAPH, hemolysis was significantly greater in HYPO (732.45+/-40% min) and lower in HYPER (578.97+/-15% min) as compared to ISO (608.30+/-42% min). Potassium efflux was significantly increased in HYPER (7508.04+/-85% min) as compared with HYPO (5308.74+/-62% min) and ISO (6561.39+/-62% min).

Discussion: Our data suggest that hyperosmolarity increases the resistance of the red blood cells when exposed to free radicals as shown by the decreased hemolysis. In such conditions, the potassium efflux analysis appears to be inappropriate to evaluate the free radical effects on erythrocytes.