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1 Intestinal Disease Research Program, McMaster University, Hamilton, ON, Canada
* To whom correspondence should be addressed. E-mail: huizinga{at}mcmaster.ca.
Ether a-go-go related gene (ERG) K channels have been implicated in the generation of pacemaker activities in the heart. To study the presence and function of ERG K channels in the pacemaker cells of the small intestine (the interstitial cells of Cajal, ICC), a combination of the patch clamp technique, tissue and live cell immunohistochemistry, RT-PCR and in vitro functional studies were performed. Nonenzymatically isolated ICC in culture were identified by vital staining and presence of rhythmic inward currents. RT-PCR showed presence of ERG mRNA in the intestinal musculature and immunohistochemistry on tissue and cultured cells demonstrated that HERG-like protein was concentrated on ICC in the Auerbach's plexus region with scattered positivity in smooth muscle cells. Whole cell ERG K+ currents were evoked upon hyperpolarization from 0 mV (but not from -70 mV) up to -120 mV and showed strong inward rectification. The currents were inhibited by E-4031, cisapride, La3+ and Gd3+. The ERG K+ inward current had a typical transient component with very fast activation and inactivation kinetics followed by significant steady state current. The ERG K+ current was insensitive to barium up to 50 µM. E-4031 also inhibited TEA insensitive outward current indicating that the ERG K+ current is operating at depolarizing potentials. In contrast to TEA, blockers of the ERG K+ currents caused marked increase in tissue excitability as reflected by an increase in slow wave duration and an increase in superimposed action potential activity. Effects of 4-AP were minor in comparison with E4031. In summary, ERG K channels in ICC contribute to the membrane potential and play a role in the regulation of pacemaker activity of the small intestine.
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