Alternative methods for measurement of membrane potentials in epithelia

Methods for the measurement of membrane potentials in cells not easily penetrated by microelectrodes were assessed for use in epithelia. The lipophilic cation triphenylmethylphosphonium appeared to distribute in a Nernstian fashion in the epithelial cells of Necturus gallbladder as judged by parallel microelectrode measurements. In the toad urinary bladder, the distribution of this cation gave a value for the membrane potential of epithelial cells under short-circuit conditions of -62 mV in normal Ringer's solution and -51 mV after 2 h treatment with ouabain. In our laboratory the dye 3,3'-dipropylthiadicarbocyanine iodide, when used with cell suspensions, yielded results comparable to those of other workers, but we were unable to record a redistributional signal from epithelial sheets or scraped cells. The dye appeared to enter cells and become irreversibly bound. The membrane-bound merocyanine dyes have not been used on epithelial cells. They appear to hold the greatest promise for dynamic experiments on epithelial membrane potentials.