Protein Kinase Inhibitor H7 Prevents the Decrease of Tight Junction Resistance Induced by Serosal Ca2+ Removal in Necturus Gallbladder Epithelium

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Abstract
Changes of the tight junction resistance (Rj) of the Necturus gallbladder epithelium in response to Ca2+ removal from the bath solutions were investigated by conventional electrophysiological methods and two-dimensional cable analysis. Luminal superfusion with Ca2+-free solution left Rj almost unchanged, while serosal removal of Ca2+ induced a slow decrease of Rj from 155 ± 10 to 25 ± 6 Ωcm2 (n = 10) within 2 h. Simultaneously the apical membrane resistance decreased while the basolateral membrane resistance as well as the gap junction resistance increased. Application of the protein kinase inhibitor H7 (50 µmol/l) blocked these resistance changes. Similar protective effects of H7 on the transepithelial resistance (Rt) were previously observed on MDCK cells [Citi: J Cell Biol 1992; 117:169]. In contrast, 5 µmol/l chelerythrine chloride, a specific blocker of the protein kinase C, did not prevent the decrease of Rj induced by serosal removal of Ca2+. These results indicate that the integrity of the tight junctions of Necturus gallbladder epithelium depends on the serosal, but not on the luminal presence of Ca2+ and that the resistance decline includes a process that can be inhibited by H7, but not by chelerythrine chloride.

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