Inactivation of the ERG current in NG108-15 cells

Differentiated NG108-15 neuroblastoma x glioma hybrid cells were whole-cell voltage clamped. The rate of inactivation of ERG (ether-à-go-go related gene) potassium channels was measured with a three-pulse protocol. Contamination with delayed rectifier current at positive potentials was avoided by using the selective ERG channel blocker E-4031. The curve relating time constant of inactivation tau to membrane potential V could be fitted by a Gauss curve. In a bath with 40 mM K(+), the curve peaked at V = -36 mV. Lowering [K(+)](o) decreased tau. At V = -20 mV, the average tau was 25.4 ms in 40 mM K(+), 20.6 ms in 6.5 mM K(+), and 15.0 ms in 0 mM K(+). This resembles the relation between tau and [K(+)](o) in ERG channels expressed in Xenopus oocytes.