Fig. 9.

The ancestral function of the carbamylation motif in Cx26 but not Cx32 is to close gap junctions. a Images showing rapid permeation of NBDG (within 1 min of establishing whole-cell recording) through the Lepidosiren Cx26 gap junction when PCO₂ is 35 mmHg. In the images, red shows the distribution of the mCherry-tagged Lepidosiren Cx26, green is NBDG fluorescence, the yellow arrow indicates the gap junction between the cells. The numbers in bottom right hand corner are minutes after establishing whole-cell recording configuration. Scale bar, 20 µm. b Permeation of NBDG through the gap junction is delayed by elevated PCO₂. The cells were perfused with hypercapnic saline (PCO₂ 55 mmHg) for 2 min following breakthrough, and then transferred to control saline (PCO₂ 35 mmHg). Significant permeation of the dye into the coupled cell is apparent only by 6th minute. c Summary data showing the effect of PCO₂ on delaying permeation of dye through the gap junction to the coupled cell. d Cx32 Gap junctions are insensitive to CO₂. NBDG permeates rapidly (within seconds after establishing the whole-cell configuration) through the gap junction at all levels of PCO₂. e Summary data showing that there is no difference in the time required for dye transfer between coupled cells at different levels of PCO₂. N = 6 for each treatment (independent replicates); box and whisker plots show the median and interquartile range (IQR), with the whisker indicating the furthest point that lies no more than 1.5 times the IQR from the median. The time for dye transfer was calculated to be when the acceptor cell had reached 10% of the fluorescence of the donor cell