title: Optogenetic activation of Gq signalling modulates pacemaker activity of cardiomyocytes.
abstract: OBJECTIVE
  Investigation of Gq signalling with pharmacological agonists of Gq-coupled receptors lacks spatio-temporal precision. The aim of this study was to establish melanopsin, a light-sensitive Gq-coupled receptor, as a new tool for the investigation of spatial and temporal effects of Gq stimulation on pacemaking in cardiomyocytes at an early developmental stage.
  
  
  RESULTS
  A vector for ubiquitous expression of melanopsin was tested in HEK293FT cells, which showed light-induced production of inositol-1,4,5-trisphosphate and elevation of intracellular Ca(2+) concentration. Mouse embryonic stem cells were stably transfected with this plasmid and differentiated into spontaneously beating embryoid bodies (EBs). Cardiomyocytes within EBs showed melanopsin expression and illumination (60 s, 308.5 nW/mm(2), 470 nm) of EBs increased beating rate within 10.2 ± 1.7 s to 317.1 ± 16.3% of baseline frequency. Illumination as short as 5 s was sufficient for generating the maximal frequency response. After termination of illumination, baseline frequency was reached with a decay constant of 27.1 ± 2.5 s. The light-induced acceleration of beating frequency showed a sigmoid dependence on light intensity with a half maximal effective light intensity of 41.7 nW/mm(2). Interestingly, EBs showed a high rate of irregular contractions after termination of high-intensity illumination. Local Gq activation by illumination of a small region in a functional syncytium of cardiomyocytes led to pacemaker activity within the illuminated area.
  
  
  CONCLUSIONS
  Light-induced Gq activation in melanopsin-expressing cardiomyocytes increases beating rate and generates local pacemaker activity. We propose that melanopsin is a powerful optogenetic tool for the investigation of spatial and temporal aspects of Gq signalling in cardiovascular research.
authors.affiliation: Institute of Physiology I, Life & Brain Center, University of Bonn, Sigmund-Freud-Strasse 25, Bonn 53105, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Beiert
authors.affiliation: Institute of Physiology I, Life & Brain Center, University of Bonn, Sigmund-Freud-Strasse 25, Bonn 53105, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Bruegmann
authors.affiliation: Institute of Physiology I, Life & Brain Center, University of Bonn, Sigmund-Freud-Strasse 25, Bonn 53105, Germany philipp.sasse@uni-bonn.de.
authors.forename: Philipp
authors.initials: P
authors.lastname: Sasse
mesh_terms: D000818:Animals; D058732:Embryoid Bodies / Q000502:physiology; D053595:Embryonic Stem Cells; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000502:physiology*; D057809:HEK293 Cells; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008027:Light; D051379:Mice; D032383:Myocytes, Cardiac / Q000502:physiology*; D062308:Optogenetics; D017299:Rod Opsins / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D000099210:Melanopsin
chemical_list: D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D017299:Rod Opsins; D000099210:Melanopsin
keywords: Cardiomyocyte; G proteins; Optogenetics; Pacemaker