Pharmacological and biophysical isolation of K+ currents encoded by ether-à-go-go-related genes in murine hepatic portal vein smooth muscle cells

Previous studies have shown that murine portal vein myocytes express ether-à-go-go related genes (ERGs) and exhibit distinctive currents when recorded under symmetrical K(+) conditions. The aim of the present study was to characterize ERG channel currents evoked from a negative holding potential under conditions more pertinent to a physiological scenario to assess the possible functional impact of this conductance. Currents were recorded with ruptured or perforated patch variants of the whole cell technique from a holding potential of -60 mV. Application of three structurally distinct and selective ERG channel blockers, E-4031, dofetilide, and the peptide toxin BeKM-1, all inhibited a significant proportion of the outward current and abolished inward currents with distinctive "hooked" kinetics recorded on repolarization. Dofetilide-sensitive currents at negative potentials evoked by depolarization to +40 mV had a voltage-dependent time to peak and rate of decay characteristic of ERG channels. Application of the novel ERG channel activator PD-118057 (1-10 microM) markedly enhanced the hooked inward currents evoked by membrane depolarization and hyperpolarized the resting membrane potential recorded by current clamp and the perforated patch configuration by approximately 20 mV. In contrast, ERG channel blockade by dofetilide (1 microM) depolarized the resting membrane potential by approximately 8 mV. These data are the first record of ERG channel currents in smooth muscle cells under quasi-physiological conditions that suggest that ERG channels contribute to the resting membrane potential in these cells.