Differences in regulation of Ca2+-activated Cl- channels in colonic and parotid secretory cells

We investigated the regulation of Ca2+-activated Cl- channels in cells from the human colonic cell line T84 and acinar cells from rat parotid glands. The participation of multifunctional Ca2+- 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. Ca2+-dependent Cl- currents were recorded using the whale cell patch-clamp technique. Direct inhibition of CaM kinase II by 40 mu M peptide 281-302 or by 10 mu M 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 Ca2+-dependent Cl- current. We also used the calmodulin-binding domain peptide 290-309 (0.5 mu M), which competitively inhibits the activation of CaM kinase II. This peptide reduced the Cl- current in T84 cells by similar to 70% but was without effect on the channels in parotid acinar cells. We conclude that the Ca2+-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 Ca2+-dependent mechanism that does not utilize CaM kinase II or any calmodulin-dependent process.