Structural and functional degradation of Ca²⁺:Mg²⁺-ATPase rich sarcoplasmic reticulum vesicles photosensitized by Erythrosin B

Erythrosin B (Red Dye No. 3) and Rose Bengal photosensitize the destruction of the Ca²⁺:Mg²⁺-ATPase pump protein in sarcoplasmic reticulum (SR) vesicles with respective quantum efficiencies of (1.53 ± 0.19) × 10^-3 and (1.25 ± 0.18) × 10^-3. Damage to vesicle function was assayed by measurements of increases in passive Ca²⁺ permeability. Rates of passive Ca²⁺ movement into the SR lumen were increased by dye photosensitization in proportion to radiation absorbed. Active Ca²⁺ transport into SR vesicles was blocked independent of radiation absorbed by Erythrosin B and Rose Bengal at free concentrations of 0.69 μM and 1.16 μM, respectively. The photochemical lability of the Ca²⁺ pump protein and alterations in passive and active Ca²⁺ transport may be dependent on the concentration of the dye in the membrane. The photosensitization results may have implications with respect to the suitability of Erythrosin B usage in vivo, since the brightness of our irradiation source is comparable to that of sunlight at 480 nm.