PROTEIN-KINASE INHIBITOR H7 PREVENTS THE DECREASE OF TIGHT JUNCTION RESISTANCE INDUCED BY SEROSAL CA2+ REMOVAL IN NECTURUS GALLBLADDER EPITHELIUM

Changes of the tight junction resistance (R(j)) of the Necturus gallbl adder epithelium in response to Ca2+ removal from the bath solutions w ere investigated by conventional electrophysiological methods and two- dimensional cable analysis. Luminal superfusion with Ca2+-free solutio n left R(j) almost unchanged, while serosal removal of Ca2+ induced a slow decrease of R(j) from 155 +/- 10 to 25 +/- 6 Ohm cm(2) (n = 10) w ithin 2 h. Simultaneously the apical membrane resistance decreased whi le the basolateral membrane resistance as well as the gap junction res istance increased. Application of the protein kinase inhibitor H7 (50 mu mol/l) blocked these resistance changes. Similar protective effects of 117 on the transepithelial resistance (R(t)) were previously obser ved on MDCK cells [Citi: J Cell Biol 1992; 117:169]. In contrast, 5 mu mol/l chelerythrine chloride, a specific blocker of the protein kinas e C, did not prevent the decrease of R(j) induced by serosal removal o f Ca2+. These results indicate that the integrity of the tight junctio ns of Necturus gallbladder epithelium depends on the serosal, but not on the luminal presence of Ca2+ and that the resistance decline includ es a process that can be inhibited by H7, but not by chelerythrine chl oride.