Differences in regulation of Ca(2+)-activated Cl- channels in colonic and parotid secretory cells

We investigated the regulation of Ca(2+)-activated Cl- channels in cells from the human colonic cell line T84 and acinar cells from rat parotid glands. The participation of multifunctional Ca(2+)- and calmodulin-dependent protein kinase (CaM kinase) II in the activation of these channels was studied using selective inhibitors of calmodulin and CaM kinase II. Ca(2+)-dependent Cl- currents were recorded using the whole cell patch-clamp technique. Direct inhibition of CaM kinase II by 40 microM peptide 281-302 or by 10 microM KN-62, another CaM kinase inhibitor, did not block the Cl- current in parotid acinar cells, whereas in T84 cells KN-62 markedly inhibited the Ca(2+)-dependent Cl- current. We also used the calmodulin-binding domain peptide 290-309 (0.5 microM), which competitively inhibits the activation of CaM kinase II. This peptide reduced the Cl- current in T84 cells by approximately 70% but was without effect on the channels in parotid acinar cells. We conclude that the Ca(2+)-dependent Cl- channels in T84 cells are activated by CaM kinase II but that the channels in parotid acinar cells must be regulated by a fundamentally different Ca(2+)-dependent mechanism that does not utilize CaM kinase II or any calmodulin-dependent process.