Functional and molecular expression of a voltage-dependent K+ channel (Kv1.1) in interstitial cells of Cajal

1. Located within the gastrointestinal (GI) musculature are networks of cel ls known as interstitial cells of Cajal (ICC). ICC are associated with seve ral functions including pacemaker activity that generates electrical slow w aves and neurotransmission regulating GI motility. In this study we identif ied a voltage-dependent K+ channel (Kv1.1) expressed in ICC and neurons but not in smooth muscle cells. 2. Transcriptional analyses demonstrated that Kv1.1 was expressed in whole tissue but not in isolated smooth muscle cells. Immunohistochemical co-loca lization of Kv1.1 with c-kit (a specific marker for ICC) and vimentin (a sp ecific marker of neurons and ICC) indicated that Kv1.1-like immunoreactivit y (Kv1.1-LI) was present in ICC and neurons of GI tissues of the dog, guine a-pig and mouse. KV1.1-LI was not observed in smooth muscle cells of the ci rcular and longitudinal muscle layers. 3. Kv1.1 was cloned from a canine colonic cDNA library and expressed in Xen opus oocytes. Pharmacological investigation of the electrophysiological pro perties of Kv1.1 demonstrated that the mamba snake toxin dendrotoxin-K (DTX -K) I,locked the Kv1.1 outward current when expressed as a homotetrameric c omplex (EC50 = 0.34 nM). Other Kv channels were insensitive to DTX-K. When Kv1.1 was expressed as a heterotetrameric complex with Kv1.5, block hv DTX- K dominated, indicating that one or more subunits of Kv1.1 rendered the het erotetrameric channel sensitive to DTX-K. 4. In patch-clamp experiments on cultured murine fundus ICC, DTX-K blocked a component of the delayed rectifier outward current. The remaining, DTX-in sensitive current (i.e. current in the presence of 10(-8) M DTX-K) was outw ardly rectifying, rapidly activating, non-inactivating during 500 ms step d epolarizations, and could be blocked by both tetraethylammonium (TEA) and 4 -aminopyridine (4-AP). 5. In conclusion, Kv1.1 is expressed bg ICC of several species. DTX-K is a specific blocker of Kv1.1 and heterotetrameric channels containing Kv1.1. T his information is useful as a means of identifying ICC and in studies of t he role of delayed rectifier K+ currents in ICC functions.