Abstract: | We investigatedthe regulation of Ca2+-activatedCl channels in cells fromthe human colonic cell line T84 and acinar cells from rat parotidglands. The participation of multifunctional Ca2+- and calmodulin-dependentprotein kinase (CaM kinase) II in the activation of these channels wasstudied using selective inhibitors of calmodulin and CaM kinase II.Ca2+-dependentCl currents were recordedusing the whole cell patch-clamp technique. Direct inhibition of CaMkinase II by 40 µM peptide 281-302 or by 10 µM KN-62, anotherCaM kinase inhibitor, did not block the Cl current in parotidacinar cells, whereas in T84 cells KN-62 markedly inhibited theCa2+-dependentCl current. We also usedthe calmodulin-binding domain peptide 290-309 (0.5 µM), whichcompetitively inhibits the activation of CaM kinase II. This peptidereduced the Cl current inT84 cells by ~70% but was without effect on the channels in parotidacinar cells. We conclude that theCa2+-dependentCl channels in T84 cellsare activated by CaM kinase II but that the channels in parotid acinarcells must be regulated by a fundamentally differentCa2+-dependent mechanism that doesnot utilize CaM kinase II or any calmodulin-dependent process. |