Abstract
Long QT syndrome (LQTS) results from mutations of several genes encoding cardiac ion channels. It was reported that in LQTS2, form associated with dysfunction of the rapid component of IK (IKr), acute auditory stimuli could trigger the symptoms thus suggesting fast neural control of IKr. The aim of this study was by means of whole-cell patch-clamp method to investigate acute regulation of native IKr by α1-adrenergic receptor (AR) in HL-1 cardiomyocytes.In the cells transiently transfected with AR, bath-application of 30 μmol phenylephrine (PHE) reversibly decreased IKr density by 29.4%, shifted activation curve (Vh from -17.6 to -9.2 mV) and accelerated deactivation. These effects remained in the presence of protein kinase C (PKC) inhibitor bisindolylmaleimide (200 nmol). In non-transfected cells 30 μmol PHE did not affect IKr. In HL-1 cells expressing muscarinic M1-receptor (known to be coupled to Gq–PLC pathway as AR), 10 μmol acetylcholine (Ach) suppressed IKr even more (37.2%).To confirm involvement of membrane PIP2 breakdown in IKr modulation, HL-1 cells cotransfected with PH (PLCδ pleckstrin homology domain) -GFP and AR or M1-receptor were used for confocal microscopy. 30 μmol PHE or 10 μmol Ach induced translocation of PH-GFP fluorescence from the cell membrane to citosol, which was not observed in the cells transfected with PH-GFP alone.AR stimulation in HL-1 cells acutely suppressed IKr by depletion of membrane PIP2 and was not dependent on PKC. This effect could explain onset of symptoms in the LQTS2 patients. [J Physiol Sci. 2006;56 Suppl:S156]
