Taurine inhibition of gap-junctional channels and involvement of the CT. Intercellular spread of calcein was assessed by a “parachute” assay in which calcein-loaded donor cells were seeded onto a monolayer of receiver cells (Goldberg et al., 1995). (A) Only junctional channels in which the Cx26 subunits were not tagged were inhibited by extracellular AS, consistent with the hemichannel data (Figs. 1 and 3). A membrane-impermeant AS, HEPES, was used to block taurine transport into the cells (Petegnief et al., 1995). HEPES effectively eliminated the taurine effect on Cx26/Cx32_T junctional channel permeability of calcein (n = 4–9). (B) AS blocks wild-type (nontagged) Cx26 hemichannels. Hemichannel uptake of extracellular calcein was assessed as in Fig. 3. In contrast to the AS insensitivity of Cx26_T and Cx26_Tc hemichannel function, nontagged Cx26 hemichannels were AS sensitive, as had been shown for preparations of purified hemichannels (Locke et al., 2004b; Yu et al., 2007), but not previously in a cellular context (n = 3). (C) AS substantially reduced intercellular calcein dye transfer through junctional channels composed of untagged Cx26, in contrast to no effect on Cx26_T junctional channels (see A; n = 4–9). The effect on nontagged Cx26-junctional channels was also eliminated by HEPES. The results for each experimental condition with taurine were normalized to its own control experiment without taurine. Error bars are standard errors of the mean.