Transient outward potassium current in ICC

Abstract

stitial 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 ϳ40 and ϳ500 ms, with no clear voltage dependence. Analysis of single-channel openings and closings indicated a channel conductance of 5 pS and permeability sequence ofThe current was completely blocked by 20 M clotrimazole but was unaffected by 20 M ketoconazole, 10 M E4031, or 20 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. potassium channel; interstitial cells of Cajal MOTILITY OF THE GUT IS DRIVEN in part by waves of depolarization that propagate along its length from oral to anal ends. These "slow waves" are generated by and propagated through a network of specialized cells, the interstitial cells of Cajal (ICC; Ref. 9). As of yet there is no consensus as to the ionic mechanisms of slow wave generation (pacemaking) and propagation. By analogy with pacemaking-conduction systems in the heart, it is likely that several types of conductance are involved. These conductances will interact via their interdependencies on membrane potential and intracellular calcium to orchestrate a repeated cycle of depolarization and repolarization, the pacemaker potential, recorded from the muscle as a slow wave. Depolarizing conductances in ICC include nonspecific cation channels (3, 15, 29), sodium channels (24, 26, 27), calcium channels (5, 13), and chloride channels (6,10,22,30,35), and discussion has focused on the merits of these as "the pacemaker channel." However, the pacemaker potential is not just a depolarization, and studies have described various potassium currents in ICC that will be involved in shaping the pacemaker potential (4, 8, 16 -20, 31, 33, 34, 36) in addition to their vital role in maintaining resting membrane potential.The present study investigated potassium currents in ICC at the single-channel level. This complements whole-cell studies and provides some advantages such as ease of isolation without use of pharmacology. In the cell-attached configuration, at room temperature and without stimulation of the cell in any way, we noticed the same current in the majority of patches.Knowledge of this background current, apart from reasons in and of itself, was important so that experimentally induced or transient currents could be better distinguished or isolated. We found that the background current was carr...

Multiple Neural Oscillators and Muscle Feedback Are Required for the Intestinal Fed State Motor Program

“…Further, clotrimazole-sensitive potassium currents have been seen in ICC in mice [45]. Even though there is little slow-wave activity in the guinea-pig, if the I K channels blockers were acting on ICCs, they would be expected to influence the properties of isolated bursts, rather than the contractile episodes, because of the time course of potassium currents in these cells [46]. However, I K currents in ISNs have a much longer time course, which would be expected to influence the properties of contractile episodes rather than isolated bursts.…”

Ano1 is a better marker than c-Kit for transcript analysis of single interstitial cells of Cajal in culture

“…Short-term primary cultures of ICC were generated by enzymatic digestion of dissected small intestinal muscle tissue as previously described [22,23]. Small intestines were removed from 5-to 15-day old CD-1 mice (Charles River Laboratories) and dissected using blunt dissection.…”

Maxi-channels recorded in situ from ICC and pericytes associated with the mouse myenteric plexus

“…Despite not being immunoreactive for ANO1 (Fig. 4), they closely resembled cultured ICC (40), having a small, often triangular cell body with two or three unramified processes at its apexes. This led us to initially (before ANO1 immunohistochemistry) consider them as ICC.…”