title: Activation of the Ca2+-sensing receptors increases currents through inward rectifier K+channels via activation of phosphatidylinositol 4-kinase.
abstract: Inward rectifier K+channels are important for maintaining normal electrical function in many cell types. The proper function of these channels requires the presence of membrane phosphoinositide 4,5-bisphosphate (PIP2). Stimulation of the Ca2+-sensing receptor CaR, a pleiotropic G protein-coupled receptor, activates both Gq/11, which decreases PIP2, and phosphatidylinositol 4-kinase (PI-4-K), which, conversely, increases PIP2. How membrane PIP2levels are regulated by CaR activation and whether these changes modulate inward rectifier K+are unknown. In this study, we found that activation of CaR by the allosteric agonist, NPSR568, increased inward rectifier K+current (IK1) in guinea pig ventricular myocytes and currents mediated by Kir2.1 channels exogenously expressed in HEK293T cells with a similar sensitivity. Moreover, using the fluorescent PIP2reporter tubby-R332H-cYFP to monitor PIP2levels, we found that CaR activation in HEK293T cells increased membrane PIP2concentrations. Pharmacological studies showed that both phospholipase C (PLC) and PI-4-K are activated by CaR stimulation with the latter played a dominant role in regulating membrane PIP2and, thus, Kir currents. These results provide the first direct evidence that CaR activation upregulates currents through inward rectifier K+channels by accelerating PIP2synthesis. The regulation of IK1plays a critical role in the stability of the electrical properties of many excitable cells, including cardiac myocytes and neurons. Further, synthetic allosteric modulators that increase CaR activity have been used to treat hyperparathyroidism, and negative CaR modulators are of potential importance in the treatment of osteoporosis. Thus, our results provide further insight into the roles played by CaR in the cardiovascular system and are potentially valuable for heart disease treatment and drug safety.
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, 128 Yen-Chiu Yuan Road, Section 2, 115, Taipei, Taiwan, Republic of China.
authors.forename: Chung-Hung
authors.initials: CH
authors.lastname: Liu
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, 128 Yen-Chiu Yuan Road, Section 2, 115, Taipei, Taiwan, Republic of China.
authors.forename: Hsueh-Kai
authors.initials: HK
authors.lastname: Chang
authors.affiliation: Imaging Core, Institute of Molecular Biology, Academia Sinica, 115, Taipei, Taiwan, Republic of China.
authors.forename: Sue-Ping
authors.initials: SP
authors.lastname: Lee
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, 128 Yen-Chiu Yuan Road, Section 2, 115, Taipei, Taiwan, Republic of China. ruchi@ibms.sinica.edu.tw.
authors.forename: Ru-Chi
authors.identifier: 0000-0001-8453-5616
authors.initials: RC
authors.lastname: Shieh
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000378:metabolism*; D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D006168:Guinea Pigs; D057809:HEK293 Cells; D006801:Humans; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000502:physiology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: C489461:Kir2.1 channel; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; D044169:Receptors, Calcium-Sensing; D019870:1-Phosphatidylinositol 4-Kinase; D010738:Type C Phospholipases
keywords: Calcium-sensing receptors; Inward rectifier K+ channels; Membrane excitability; PIP2