Submitted on March 30, 2006
Accepted on July 25, 2006
Pharmacological and biophysical isolation of K+ currents encoded by ether-a-go-go related genes in murine hepatic portal vein smooth muscle cells
Shuk Yin M Yeung1 and Iain A Greenwood1*
1 Basic Medical Sciences, St George's University of London, London, United Kingdom
* To whom correspondence should be addressed. E-mail: i.greenwood{at}sgul.ac.uk.
Previous studies have shown that murine portal vein myocytes express ether-a-go-go related genes (ERG) and exhibit distinctive currents when recorded using symmetrical K+ conditions. The aim of the present study was to characterise 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 using 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 upon repolarisation. Dofetilide-sensitive currents at negative potentials evoked by depolarisation to +40 mV had a voltage-dependent time to peak and rate of decay characteristic of ERG channels. Application of a novel ERG channel activator PD-118057 (1-10 µM) markedly enhanced the hooked inward currents evoked by membrane depolarisation and hyperpolarised the resting membrane potential recorded by current clamp and the perforated patch configuration by about 20 mV. In contrast ERG channel blockade by dofetilide (1 µM) depolarised the resting membrane potential by about 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.
