Electrical properties of the cellular transepithelial pathway inNecturus gallbladder

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Abstract
Microelectrode techniques were employed to measure the electrical resistance of the cell membranes and the shunt pathway, and the equivalent electromotive forces (EMF's) at both cell borders inNecturus gallbladder epithelium. The cell is, on the average, 57 mV negative to the mucosal solution and 59 mV negative to the serosal solution. The transepithelial potential (V ms) ranges from 0.5 to 5 mV, serosal solution positive. Assuming that the shunt EMF (V s) is zero with standard Ringer's bathing both sides of the tissue, both cell membrane EMF's are oriented with the negative pole toward the cell interior and are 39.9±3.6 mV (apical,V a), and 69.4±1.8 mV (basal-lateral,V b). The values of the resistances of the cell membranes and the shunt are similar to those previously reported by others: apical (R a), 3350±390 Ω cm2, basal-lateral (R b) 2750±320 Ω cm2, shunt (R s), 480±50 Ω cm2. Ionic substitutions on the mucosal side produce changes in both EMF and resistance of the apical membrane and the shunt pathway. Increasing K concentration to 112mm reversesV a and greatly reducesR a. Complete Na replacement with an inert nonpermeant cation slightly increasesV a andR a. These results indicate that across the apical membraneP K>P Na. Analogous measurements ofV s indicate cation permselectivity, withP K>P Na>P choline∼P TEA∼P methylglucamine. In general, changes inV s are very similar to the changes inV ms, indicating that the latter measurements yield adequate information on the properties of the shunt. The fact thatP Na>P Cl across the shunt rules out the possibility thatV ms is generated by a NaCl concentration gradient across the limiting junction.