Barium blocks cell membrane and tight junction conductances inNecturus gallbladder epithelium |
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Authors: | G. Kottra E. Frömter |
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Affiliation: | 1. Zentrum der Physiologie, Klinikum der Johann Wolfgang von Goethe-Universit?t, Theodor-Stern-Kai 7, D-6000, Frankfurt am Main 70, Federal Republic of Germany
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Abstract: | The site and concentration dependence of the blocking effect of Ba2+ onNecturus gallbladder epithelium has been investigated. A new approach was used which combines time-dependent electrical cell coupling analysis with intermittently performed measurements of transepithelial and apparent intracellular impedance. From the coupling pulse data the sum of apical and basolateral membrane conductances is obtained, which is then held constant during fitting of the impedance data. This combination technique yields more reliable estimates of apical and basolateral membranes resistances (R a,R bl) and of tight junction resistance (R j) than our previous impedance analysis technique. Using the new approach we have found that luminal Ba2+ concentrations between 0.5 and 1.0 mmol/l increaseR a with saturation-type kinetics without affectingR bl andR j, while higher luminal Ba2+ concentrations progressively increaseR j. Corresponding effects were observed under serosal Ba2+. The results validate the new impedance analysis approach and demonstrate that millimolar concentrations of Ba2+ block tight junction conductances. Accordingly, Ba2+ can no longer be considered a tool to exclusively alter cell membrane resistances in epithelia. |
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Keywords: | Necturus Gallbladder epithelium Epithelial impedance Two-dimensional cable analysis Barium Tight junction resistance Cell membrane resistance |
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