Modulation of the HERG channel by M₁-muscarinic receptor and phosphatidylinositol-4-phosphate 5-kinase

Abstract

The present study was designed to investigate the modulation of the HERG channel by membrane phosphatidylinositol 4,5-bisphosphate (PIP₂) using the whole-cell patch-clamp method. Both HERG channel and M₁-muscarinic receptor (M₁R) were heterologously expressed in CHO cells either with or without phosphatidylinositol-4-phosphate 5-kinase (PI(4)P5-K) by transient transfection. The HERG current was activated by depolarizing voltage-clamp steps to various test potentials and the degree of HERG current activation was determined by the amplitude of tail current elicited on repolarization to -60 mV. The density of HERG current (36.6±6.2 pA/pF, n = 6) following a 2-s depolarizing step to +10 mV in cells heterologously expressing PI(4)P5-K was approximately two times larger than that (16.3±3.8 pA/pF, n = 6) in cells without its expression. The voltage-dependence of current activation and kinetics of current deactivation were minimally affected by heterologous expression of PI(4)P5-K. In cells without heterologous expression of PI(4)P5-K, the stimulation of M₁R with 30 μM ACh reduced the HERG current by 21.9±3.9% (n = 7), accompanied by acceleration of current deactivation, which was significantly attenuated by heterologous expression of PI(4)P5-K (10.6±2.1% decrease, n = 6). These results suggest that the HERG channel is closely dependent on changes in PIP₂ level which are regulated by PI(4)P5-K and M₁R. [Jpn J Physiol 55 Suppl:S129 (2005)]