Porphyrin sensitization and intracellular calcium changes in the prokaryote Propionibacterium acnes

Photosensitization induces intracellular free calcium changes ([Ca2+] i) in some eukaryotic cell systems that either contribute to or prote ct agains cell inactivation. We have investigated whether or not simi lar changes can be induced in prokaryotes.The skin bacterium Propion ibacterium acnes was sensitized using protoporphyrin IX (PP IX) or 5- aminolevulinic acid (ALA). Exogenous ALA resulted in either a prefere ntial accumulation of protoporphyrin (ALA-PP) or of coproporphyrin an d/or uroporphyrin (ALA-CP/UP) in P.acnes. For PP IX or ALA-PP sensiti zation, exposure to broad-band red light resulted in an increase in [ Ca2+]i. For ALA-PP sensitization, this increase was transient and [Ca 2+]i returned to basal levels within 5-10 min after irradation. Howev er, the elevated [Ca2+]i levels obtained after PP IX sensitization we re maintained for at least 1 h after irradiation. In both cases, the reduction in the external calcium concentration led to an enhancement in the cell survival, indicating that induced [Ca2+]i changes may pa rticipate in photoinactivation. Sensitization by hydrophilic copropor phyrin and/or uroporphyrin (ALA-CP/UP) did not affect [Ca2+]i levels, but higher levels of cell inactivation were obtained. It therefore a ppears that damage to membrane-associated components is at least part ly responsible for [Ca2+]i alterations after photosensitization.