Regulation of a human chloride channel - A paradigm for integrating input from calcium, type II calmodulin-dependent protein kinase, and inositol 3,4,5,6-tetrakisphosphate

We have studied the regulation of Ca2+-dependent chloride (Cl-Ca) channels in a human pancreatoma epithelial cell line (CFPAC-1), which does not express functional cAMP-dependent cystic fibrosis transmembrane conductance regulator chloride channels. In cell-free patches from these cells, physiological Ca2+ concentrations activated a single class of 1-picosiemens Cl--selective channels. The same channels were also stimulated by a purified type II calmodulin-dependent protein kinase (CaMKII), and in cell-attached patches by purinergic agonists. In whole-cell recordings, both Ca2+- and CaMKII-dependent mechanisms contributed to chloride channel stimulation by Ca2+, but the CaMKII-dependent pathway was selectively inhibited by inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5,6)P-4). This inhibitory effect of Ins(3,4,5,6)P, on Cl-Ca channel stimulation by CaMKII was reduced by raising [Ca2+] and prevented by inhibition of protein phosphatase activity with 100 nM okadaic acid. These data provide a new context for understanding the physiological relevance of Ins(3,4,5,6)P, in the longer term regulation of Ca2+-dependent Cl- fluxes in epithelial cells.