Functional investigations of ERG potassium channels on INS1 cells with the blocker E-4031

Abstract

The ERG (ether-a-go-go-related gene) channels are voltage controlled potassium channels, that first have been described in a mutant of Drosophila melanogaster in 1991. In heart muscle cells these channels are essential for the repolarisation of action potentials. Mutations in the ERG gene may lead to a prolonged QT-interval (long QT-syndrome). In human pancreatic β-cells, ERG channels are known to influence the insulin secretion (Rosati et al.). In our group, Erg channel mRNA expression was measured by real-time PCR in rat insulinoma cells (INS1), rat pancreatic islets and endocrine pancreatic tissue (Mühlbauer et al.). Functional properties of ERG channels were investigated by electrophysiology and calcium imaging. The channels were selectively blocked by the methanesulfonanilide E-4031 (1µmol/l). Whole cell voltage clamp measurements from INS1 cells showed E-4031 sensitive currents, leading to a total decrease of the membrane current by 12.2±2.4% (n=6). Current clamp measurements of the membrane potential (perforated patch technique) from spontaneously silent INS1 cells led to a depolarisation of (4.4±0.8) mV (n=9). In spontaneously spiking cells the spiking frequency was raised threefold by the blocker E-4031. These effects of E4031 may influence voltage controlled calcium channels. Thus, an increase of the internal calcium concentration during blocking of the ERG channels was measured by use of confocal laser scanning microscopy. The investigations led to the conclusion, that INS1 cells express functional active and E-4031 sensitive ERG channels which might be linked to insulin secretion.