Characterization of depolarization-evoked ERG K+ currents in interstitial cells of Cajal.
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Interstitial cells of Cajal (ICC) harbour the ether-a-go-go related gene (ERG) channel as shown by its characteristic rapidly deactivating current upon hyperpolarization. This property, however, does not explain the marked increase in cell excitability by ERG channel blockers, namely an increase in slow wave plateau duration and action potential generation. The objective of the present study was to characterize the depolarization-activated, E4031-sensitive ERG currents in murine ICC within a range of physiologically relevant membrane potentials. Whole cell currents were recorded from ICC isolated from murine neonatal jejunum, superfused with a physiological salt solution and with high intracellular Cs(+) to block most other K(+) currents. Upon depolarizing the cell from the resting membrane potential (approximately -60 mV) towards the region of the slow wave plateau (approximately -30 mV), significant sustained (window) current was generated between the potentials of -40 to 0 mV (maximal at -30 mV) and inhibited by the ERG specific blocker E4031. Channel activation followed by rapid inactivation produced a steady state conductance at -30 mV which was 51.6 +/- 11% of the hyperpolarization-evoked peak conductance value at -100 mV. When the cell repolarized from -30 mV, again, significant currents were generated, indicating recovery from inactivation, a typical characteristic of ERG channels. These data provide evidence that the ERG channel is of significance in the regulation of ICC excitability and provide the mechanism by which ERG channel blockade increases the slow wave duration.
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