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

Intermediate conductance potassium (IK) channels are exquisitively Ca sensitive, intracellular Ca 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 channel activity, the effect of W-7 in human T lymphocytes are conflicting. We therefore evaluated the effect of W-7 on basolateral IK channels in human colonic crypt cells. Intact crypts obtained from normal human colonic biopsies by Ca chelation were used for patch clamp studies of basolateral IK channels in the cell-attached configuration. IK channel activity was studied when the bath Ca 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 from 1.2 mmol/L to 100 μmol/L decreased IK channel activity reversibly in the absence of W-7, whereas there was a uniformly high level of channel activity at both bath Ca concentrations in the presence of W-7. In separate experiments, increasing bath Ca from 100 μmol/L to 1.2 mmol/L increased IK channel activity reversibly in the absence of W-7, whereas there was again a uniformly high level of channel activity at both bath Ca concentrations in the presence of W-7. We, therefore, propose that W-7 has a specific stimulatory effect on basolateral IK channel activity, despite its ability to inhibit Ca/CaM-mediated, IK channel-dependent Cl secretion in human colonic epithelial cells.