Carbon dioxide reversibly abolishes ionic communication between cells of early amphibian embryo

Low electrical resistance intercellular junctions have been found in a wide variety of adult tissues, both in vivo and in tissue culture1 and in early embryos2. Vertebrate and invertebrate adult intercellular junctions are permeable to small ions and a variety of other molecules, of molecular weights possibly up to 1,000, as shown by the movement of tracers such as fluorescein8 and transfer of nucleotides (‘metabolic cooperation’)3. In adult systems, such intercellular exchange is correlated with the presence of gap junctions4. In embryos, some form of specific junction is necessary to account for the observed electrical coupling after early cleavage stages5 and the presence of gap junctions has been reported5–8. Since the low resistance intercellular pathway has been implicated in the control of spatial and temporal organisation during development9, the permeability of the embryonic junction assumes some importance. There is evidence suggesting that embryonic junctions are less permeable than adult junctions10–13, which we have recently confirmed14. Our experiments14 suggested that there is selectivity in the gap junctional membrane which led us to predict that the junctional permeability would be sensitive to changes in intracellular pH. We present here results which confirm this prediction.