title: NO underlies the muscarinic receptor-mediated inhibition of If in early embryonic heart cells.
abstract: OBJECTIVE
  Early embryonic cardiomyocytes beat spontaneously. The hyperpolarization-activated cyclic-nucleotide-modulated current (I(f)) appears to be involved in its modulation as it is highly expressed at this stage. The spontaneous beating of early embryonic heart cells is slowed by acetylcholine (ACh), and our earlier studies identified a key role for nitric oxide (NO) in the regulation of the voltage dependent L-type Ca(2+) current (I(Ca,L)). The aim of the present study was to clarify whether and via which signalling pathway(s) I(f) is regulated upon muscarinic receptor activation in early embryonic (E9.5 to E11.5) cardiomyocytes.
  
  
  METHODS
  The whole-cell patch clamp technique in combination with pharmacology and/or knock out mouse models was used to investigate the regulation of I(f).
  
  
  RESULTS
  We found that the ACh analogue carbachol (CCh, 10 micromol) led in the majority of cells (68%, n=50) to a significant depression of I(f) by 16.3+/-1.4% (n=34, p<0.01, voltage steps from -35 mV to -110 mV). This cholinergic inhibition was mediated by the NO/cGMP signalling pathway as it was largely reversed by superfusion with the non selective nitric oxide synthase (NOS) inhibitor N(G)-Methyl-L-arginine acetate salt (L-NMMA, 1 mmol), the inhibitor of the soluble guanylyl cyclase (sGC) 1H-[1, 2, 4]Oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ, 100 micromol) and a selective inhibitor of the phosphodiesterase (PDE) type 2 Erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, 30 micromol). Analysis of the muscarinic signalling in embryonic cardiomyocytes harvested from NOS2 (-/-) and NOS3 (-/-) mice revealed that the NOS3 isoform was entirely responsible for the muscarinic receptor-induced NO production.
  
  
  CONCLUSIONS
  Muscarinic receptor stimulation depresses I(f) by generating NO via the NOS3 and the cGMP/PDE type 2 signalling pathway in early embryonic cardiomyocytes. This suggests that NO is a key signalling molecule involved in the regulation of chronotropy of early embryonic heart cells.
authors.affiliation: Institute of Neurophysiology, University of Cologne, Cologne, Germany.
authors.forename: Nora
authors.initials: N
authors.lastname: Lang
authors.forename: Michael
authors.initials: M
authors.lastname: Reppel
authors.forename: Juergen
authors.initials: J
authors.lastname: Hescheler
authors.forename: Bernd K
authors.initials: BK
authors.lastname: Fleischmann
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D016764:Cell Polarity / Q000187:drug effects; D002478:Cells, Cultured; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006321:Heart / Q000196:embryology*; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D009712:Nucleotides, Cyclic / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction; D000071756:Soluble Guanylyl Cyclase; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D009712:Nucleotides, Cyclic; D018160:Receptors, Cytoplasmic and Nuclear; D011976:Receptors, Muscarinic; D009569:Nitric Oxide; D002217:Carbachol; D019001:Nitric Oxide Synthase; D010727:Phosphoric Diester Hydrolases; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase