Transient outward potassium current in ICC

Parsons SP, Huizinga JD. Transient outward potassium current in ICC. Am J Physiol Gastrointest Liver Physiol 298: G456-G466, 2010. First published January 7, 2010; doi: 10.1152/ajpgi.00340.2009.-Interstitial cells of Cajal ( ICC) are the pacemakers of the gut, initiating slow-wave activity. Several ion channels have been identified that contribute to the depolarization phase of the slow wave. Our aim was to contribute to knowledge about the identity and role of ICC potassium channels in pacemaking. Here we describe a transient outward potassium current in cell-attached patches of ICC. This current was activated almost instantaneously at potentials positive of the resting membrane potential and inactivated as a single exponential or biexponential with time constants that varied widely from patch to patch. Averaged traces gave a biexponential inactivation with time constants of similar to 40 and similar to 500 ms, with no clear voltage dependence. Analysis of single-channel openings and closings indicated a channel conductance of 5 pS and permeability sequence of K+ (111) > Na+ (1) > N-methyl-D-glucamine(+) (0.11). The current was completely blocked by 20 mu M clotrimazole but was unaffected by 20 mu M ketoconazole, 10 mu M E4031, or 20 mu M clofilium; 5 mM 4-aminopyridine slowed the activation of the current. The transient outward current may be important in moderating the upstroke of the pacemaker potential.