Intermediate-conductance calcium-activated potassium channels in enteric neurones of the mouse: pharmacological, molecular and immunochemical evidence for their role in mediating the slow afterhyperpolarization.

Calcium-activated potassium channels are critically important in modulating neuronal cell excitability. One member of the family, the intermediate-conductance potassium (IK) channel, is not thought to play a role in neurones because of its predominant expression in non-excitable cells such as erythrocytes and lymphocytes, in smooth muscle tissues, and its lack of apparent expression in brain. In the present study, we demonstrate that IK channels are localized on specific neurones in the mouse enteric nervous system where they mediate the slow afterhyperpolarization following an action potential. IK channels were localized by immunohistochemistry on intrinsic primary afferent neurones, identified by their characteristic Dogiel type II morphology. The slow afterhyperpolarization recorded from these cells was abolished by the IK channel blocker clotrimazole. RT-PCR and western analysis of extracts from the colon revealed an IK channel transcript and protein identical to the IK channel expressed in other cell types. These results indicate that IK channels are expressed in neurones where they play an important role in modulating firing properties.