The Role of Glycolysis and Univalent Ions in Phthalocyanine-sensitized Photohaemolysis of Human Erythrocytes

Summary

Phthalocyanines sensitize human erythrocytes to red light in vitro and in vivo. The mechanism of photosensitization of haemolysis of red blood cells was studied using haemoglobin release in vitro as an endpoint. We have previously shown that the cation present in the incubation medium determines the rate of photohaemolysis, with the rate increasing in the order Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺. With halogen anions, the rate increases in the order F⁻, Cl⁻, Br⁻. With F⁻ in isotonic solution the rate was about two orders of magnitude slower than with Cl⁻, so that haemolysis was practically prevented. Fluoride slowed haemolysis at very low concentrations (< 1 mm) with an apparent K₁ of 0·1 mm in isotonic NaCl. Most of the effect disappeared when F⁻ was added after light exposure, with a half-time of 1 min. The effect of F⁻ was specific to phthalocyanine. Neither Photofrin-induced photohaemolysis nor gramicidin-induced haemolysis were inhibited by fluoride. Addition of 10 mm deoxyglucose prior to photosensitization enhanced haemolysis and reduced cellular ATP levels by about 50% compared to controls containing glucose. Haemolysis was preceded by a reduction in ATP levels in the presence of both glucose and deoxyglucose. No significant decrease in ATP levels was found following light exposure in the presence of 0·75 mm F⁻. It is concluded that glycolysis and ATP are important in preventing photohaemolysis. The protective effect of F⁻ may be related to its inhibition of a fast early reaction which triggers the events leading to photohaemolysis induced by phthaloyanine