title: Regulatory effect of connexin 43 on basal Ca2+ signaling in rat ventricular myocytes.
abstract: BACKGROUND
  It has been found that gap junction-associated intracellular Ca(2+) [Ca(2+)](i) disturbance contributes to the arrhythmogenesis and hyperconstriction in diseased heart. However, whether functional gaps are also involved in the regulation of normal Ca(2+) signaling, in particular the basal [Ca(2+)](i) activities, is unclear.
  
  
  RESULTS
  Global and local Ca(2+) signaling and gap permeability were monitored in cultured neonatal rat ventricular myocytes (NRVMs) and freshly isolated mouse ventricular myocytes by Fluo4/AM and Lucifer yellow (LY), respectively. The results showed that inhibition of gap communication by heptanol, Gap 27 and flufenamic acid or interference of connexin 43 (Cx43) with siRNA led to a significant suppression of LY uptake and, importantly, attenuations of global Ca(2+) transients and local Ca(2+) sparks in monolayer NRVMs and Ca(2+) sparks in adult ventricular myocytes. In contrast, overexpression of rat-Cx43 in NRVMs induced enhancements in the above measurements, and so did in HEK293 cells expressing rat Cx43. Additionally, membrane-permeable inositol 1,4,5-trisphosphate (IP(3) butyryloxymethyl ester) and phenylephrine, an agonist of adrenergic receptor, could relieve the inhibited Ca(2+) signal and LY uptake by gap uncouplers, whereas blockade of IP(3) receptor with xestospongin C or 2-aminoethoxydiphenylborate mimicked the effects of gap inhibitors. More importantly, all these gap-associated effects on Ca(2+) signaling were also found in single NRVMs that only have hemichannels instead of gap junctions. Further immunostaining/immunoblotting single myocytes with antibody against Cx43 demonstrated apparent increases in membrane labeling of Cx43 and non-junctional Cx43 in overexpressed cells, suggesting functional hemichannels exist and also contribute to the Ca(2+) signaling regulation in cardiomyocytes.
  
  
  CONCLUSIONS
  These data demonstrate that Cx43-associated gap coupling plays a role in the regulation of resting Ca(2+) signaling in normal ventricular myocytes, in which IP(3)/IP(3) receptor coupling is involved. This finding may provide a novel regulatory pathway for mediation of spontaneous global and local Ca(2+) activities in cardiomyocytes.
authors.affiliation: Department of Pharmacology, School of Chemical Biology & Pharmaceutical Sciences, Capital Medical University, Beijing, China.
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.forename: Qingli
authors.initials: Q
authors.lastname: Meng
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Yu
authors.forename: Xian
authors.initials: X
authors.lastname: Jing
authors.forename: Pingxiang
authors.initials: P
authors.lastname: Xu
authors.forename: Dali
authors.initials: D
authors.lastname: Luo
mesh_terms: D000322:Adrenergic Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002450:Cell Communication / Q000187:drug effects; D002478:Cells, Cultured; D018031:Connexin 43 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000737:chemistry / Q000378:metabolism; D017629:Gap Junctions / Q000378:metabolism; D057809:HEK293 Cells; D006352:Heart Ventricles / Q000166:cytology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D007546:Isoquinolines / Q000737:chemistry / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011941:Receptors, Adrenergic / Q000737:chemistry / Q000378:metabolism
chemical_list: D000322:Adrenergic Agonists; D018031:Connexin 43; D005456:Fluorescent Dyes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007546:Isoquinolines; D034741:RNA, Small Interfering; D011941:Receptors, Adrenergic; D010656:Phenylephrine; D015544:Inositol 1,4,5-Trisphosphate; C017475:lucifer yellow; D002118:Calcium