Quantitation of erythrocyte photohemolysis by light microscopy

In a solution of erythrocytes and a photo-active compound, light activation of the compound produces hemolysis of the cells. This study describes a new assay in which focused light through a microscope is used to induce a circumscribed hemolysis of erythrocytes that have been mixed with fluorescein isothiocyanate-dextran 150,000 (FITC-DEX) and placed in a hemacytometer. The hemolytic response was monitored by detecting transmitted light intensity in the area (1.8 x 10(-4) cm2) of activation. Only cells within the specific microscopic field of activation hemolyze. This allows for multiple sites of activation within one sample. The hemolytic response was dependent on the concentration of FITC-DEX (0.5-4 mg/ml) and on light intensity (53-210 J/cm2) but not on small changes in hematocrit (3%-5%) or on the presence of platelets and leukocytes. Rabbit erythrocytes, however, were almost twice as sensitive as those from guinea pigs. Since the photohemolytic response will depend on the composition and strength of the erythrocyte membrane and presence of oxidant defense mechanisms, we suggest that this assay could be used to detect drug- or disease-induced changes in the red blood cell membrane.