METALLOPORPHYRIN CHLORIDE IONOPHORES - INDUCTION OF INCREASED ANION PERMEABILITY IN LUNG EPITHELIAL-CELLS

Tetraphenyl-21H,23H-porphine manganese(III) chloride [TPPMn(III)] is a positively charged lipophilic anion carrier that is widely used as a Cl- sensor. TPPMn(III) increased anion permeability of cultured mouse lung epithelial (MLE) cells as measured by short-circuit current (I-SC ) to a level similar to that induced by forskolin analogues. Anion per meability was also studied in cultured human lung epithelial (A549) ce lls by measurement of the rates of change of fluorescence of the anion sensitive fluorescent dye, 6-methoxy-N-(3-sulfopropyl)quinolinium (SP Q). In these studies, cells were incubated with SPQ in SO42- medium, w ashed free of extracellular SPQ, and then perfused with medium contain ing anions that are known to quench SPQ fluorescence. The effect of TP PMn(III) on anion transport was then determined either microscopically in single cell studies or using cell monolayers mounted in a front fa ce fluorimeter. TPPMn(III) in the range from 1 to 100 mu g/ml induced a dose-dependent increase in Br- transport. The half-maximal quenching effect was estimated to be similar to 5 mu g/ml. TPPMn(III) increased the rates of fluorescence quench of anions by up to fourfold. TPPMn(I II) was without effect on [Ca2+](i) level in A549 cells as measured wi th fura 2-AM. This indicates that TPPMn(III) effects were not mediated through effects on Ca2+-activated Cl- channels, or by compromise of e nergy metabolism or membrane integrity of the cells. This study sugges ts that TPPMn(III) and, by extension, other lipophilic Mn(III) or Co(I II) derivatives wherein the selectivity or lipophilicity is altered, c ould increase the anion permeability of biological membranes, and sugg ests a new approach for treatment of diseases such as cystic fibrosis, where transport of Cl- is defective.