Observation of Water Permeability in Xenopus Oocytes Expressing Gap Junction Proteins

Gap junctions induce electrical and biochemical coupling of animal cells and play crucial roles in cell communication, development, electrical signaling, and tissue homeostasis. Some gap junction proteins also play physiological roles through the formation of transmembrane channels. As part of an undergraduate cell physiology lab related to aquaporins function we inadvertently observed water permeability in Xenopus oocytes injected with the gap junction protein connexin32. Water permeability was categorized in simple experiments involving "time-to-burst" after submersion in water. Further experiments revealed that oocytes expressing several connexins (Cx32, Cx26, Cx43) burst more quickly than uninjected controls or antisense-injected controls (antiXeCx38 morpholino) although significantly more slowly than aquaporin-injected oocytes. We also conducted a preliminary analysis of oocyte swelling using cell volume calculations. These experiments supported the "time-to-burst" studies. Oocytes injected with Cx43, Cx32, Cx26, CeUnc9 and DmShakB had swelling rates above that of negative controls, although significantly lower than aquaporin-injected oocytes. Pannexin1-injected oocytes had swelling rates similar to negative controls. There was variability between gap junction proteins in these preliminary experiments with Cx26 and Cx43 inducing the highest water permeability. Since the channels formed by gap junction proteins are tightly regulated and remain predominantly closed as transmembrane channels we believe that water permeability may result from dysregulation under extreme osmotic challenge. The phenomenon will be further investigated using blockers and gap junction mutants.