Calmodulin Antagonist W-7 Enhances Intermediate Conductance Ca(2+)- Sensitive Basolateral Potassium Channel (IK(Ca)) Activity in Human Colonic Crypts

Intermediate conductance potassium (IK(Ca)) channels are exquisitively Ca(2+) sensitive, intracellular Ca(2+) regulating channel activity by complexing with calmodulin (CaM), which is bound to the cytosolic carboxyl tail. Although CaM antagonists might be expected to decrease IK(Ca) channel activity, the effect of W-7 in human T lymphocytes are conflicting. We therefore evaluated the effect of W-7 on basolateral IK(Ca) channels in human colonic crypt cells. Intact crypts obtained from normal human colonic biopsies by Ca(2+) chelation were used for patch clamp studies of basolateral IK(Ca) channels in the cell-attached configuration. IK(Ca) channel activity was studied when the bath Ca(2+) concentration was changed from 1.2 mmol/L to 100 μmol/L and back to 1.2 mmol/L, as well as from 100 μmol/L to 1.2 mmol/L and back to 100 μmol/L, both in the absence and presence of 25 μmol/L W-7. Decreasing bath Ca(2+) from 1.2 mmol/L to 100 μmol/L decreased IK(Ca) channel activity reversibly in the absence of W-7, whereas there was a uniformly high level of channel activity at both bath Ca(2+) concentrations in the presence of W-7. In separate experiments, increasing bath Ca(2+) from 100 μmol/L to 1.2 mmol/L increased IK(Ca) channel activity reversibly in the absence of W-7, whereas there was again a uniformly high level of channel activity at both bath Ca(2+) concentrations in the presence of W-7. We, therefore, propose that W-7 has a specific stimulatory effect on basolateral IK(Ca) channel activity, despite its ability to inhibit Ca(2+)/CaM-mediated, IK(Ca) channel-dependent Cl(−) secretion in human colonic epithelial cells. [Image: see text]