Phosphatidylinositol4-phosphate 5-kinase prevents the decrease in the HERG potassium current induced by Gq protein-coupled receptor stimulation

Abstract

The human ether-a-go-go-related gene (HERG) potassium current (I_HERG) has been shown to decrease in amplitude following stimulation with Gq protein-coupled receptors (GqRs), such as α₁-adrenergic and M₁-muscarinic receptors (α₁R and M₁R, respectively), at least partly via the reduction of membrane phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂). The present study was designed to investigate the modulation of HERG channels by PI(4,5)P₂ and phosphatidylinositol4-phosphate 5-kinase (PI(4)P5-K), a synthetic enzyme of PI(4,5)P₂. Whole-cell patch-clamp recordings were used to examine the activity of HERG channels expressed heterologously in Chinese Hamster Ovary cells. The stimulation of α₁R with phenylephrine or M₁R with acetylcholine decreased the amplitude of I_HERG accompanied by a significant acceleration of deactivation kinetics and the effects on I_HERG were significantly attenuated in cells expressing PI(4)P5-K. The density of I_HERG in cells expressing GqRs alone was significantly increased by the coexpression of PI(4)P5-K without significant differences in the voltage dependence of activation and deactivation kinetics. The kinase-deficient substitution mutant, PI(4)P5-K-K138A did not have these counteracting effects on the change in I_HERG by M₁R stimulation. These results suggest that the current density of I_HERG is closely dependent on the membrane PI(4,5)P₂ level, which is regulated by PI(4)P5-K and GqRs and that replenishing PI(4,5)P₂ by PI(4)P5-K recovers I_HERG.