Photosensitized damage of bilayer lipid membrane in the presence of haematoporphyrin dimethylether

The variations in electrical conductivity and surface tension of planar bilayer lipid membranes (BLMs) sensitized by a haematoporphyrin dimethylether (HpDME) on visible light irradiation are reported. The irradiation of BLMs immediately leads to a decrease in membrane surface tension. On irradiation the conductivity of BLMs remains constant for a certain period of time (induction time), followed by an increase, terminated by membrane breakage. The induction time is not dependent on stirring of the solution, the addition of azide or ferricyanide to the solution, the addition of antioxidant to the lipid or substitution of air for argon in the cell. The induction time decreases for repeated irradiations or for any new BLM formed in the same cell immediately after the previous membrane has been broken. The conductivity shift consists of reversible and irreversible components. These results suggest that the irradiation of BLMs sensitized by HpDME leads to an accumulation of photoproducts in the membrane which induce pore formation and to a decrease in BLM stability when the concentration of the photoproducts exceeds a critical level.