Isolated epithelial cells from amphibian urinary bladder express functional gap junctional hemichannels

Exposure of the urinary bladder epithelium of Necturus maculosus (NUB) to protease and collagenase yields ~50% isolated polarized cells. These cells express a membrane current slowly activated by depolarization or by removal Of: external divalent cations. The biophysical and pharmacological properties of the current are largely consistent with those of gap junctional hemichannels. After removal of divalent cations, the cells can also be loaded with 5(6)-carboxyfluorescein, a hydrophilic fluorescent anionic dye, and exposure to dye reduces the current in a manner dependent on membrane voltage and side of application. In contrast, Necturus gallbladder (NGB) cells exhibit no membrane conductance attributable to gap junctional hemichannels, although previous studies reveal the persistence of gap junction plaques on the plasma membrane. We conclude that functional gap junctional hemichannels can be expressed on the surface of certain isolated epithelial cells and that this is not a necessary consequence of the isolation procedure. These structures may contribute to cell damage under pathological conditions involving cell detachment.