Electrophysiological studies on lateral intercellular spaces of Necturus gallbladder epithelium

The lateral intercellular spaces of Necturus gallbladder epithelium were punctured with double-barrelled ion selective microelectrodes in order to determine the ion concentrations of lateral space fluid and the contribution of the lateral spaces to transepithelial resistance. Neither under control conditions, nor after diluting the bathing fluids to increase the rate of volume absorption, nor during passage of direct current of 200 microA/cm2, were any reliable concentration differences observed between lateral space fluid and external bathing fluids. These observations suggest that water can follow salt transport without requiring osmotic concentration gradients of greater than 1 or 2 mosmol/l and indicate that recently observed high values of water permeability must still be considered as underestimates. After developing a test to recognize and exclude leaky punctures, the contribution of the lateral spaces to transepithelial resistance could be determined. It amounted to around 29%. This value agrees well with results from recent impedance measurements which were performed under control conditions in the same preparation.