DISSOCIATION OF DEPOLARIZATION-ACTIVATED AND SWELLING-ACTIVATED CL- CHANNELS

In many cells, patch excision and depolarization induce outwardly rect ifying Cl- channels (ORDIC channels) whose function and normal mode of regulation are unknown. One possible function is the mediation of swe lling-activated Cl(-)conductance, because in many cells rectifying Cl- currents are activated by cell swelling. However, swelling-activated Cl(-)channels in some epithelia have larger conductances than ORDIC ch annels and inactivate more rapidly, although both have similar anion s electivity and are blocked by stilbenes. Thus it has not been possible to determine whether the two types of channel current arise from dist inct proteins or alternate states of a single protein. We studied 14 c ell lines and found 2 Lines, C127 mouse mammary epithelial cells and I EC-6 rat intestinal crypt cells, with very low levels of ORDIC channel s. However, despite the near absence of ORDIC channels in these rodent cells, a large smelling-activated Cl(-)conductance was demonstrated b y whole cell, efflux, and single-channel methods. Thus it is likely th at ORDIC and swelling-activated channel currents arise from different channel proteins.