title: Gαi2- and Gαi3-specific regulation of voltage-dependent L-type calcium channels in cardiomyocytes.
abstract: BACKGROUND
  Two pertussis toxin sensitive G(i) proteins, G(i2) and G(i3), are expressed in cardiomyocytes and upregulated in heart failure. It has been proposed that the highly homologous G(i) isoforms are functionally distinct. To test for isoform-specific functions of G(i) proteins, we examined their role in the regulation of cardiac L-type voltage-dependent calcium channels (L-VDCC).
  
  
  METHODS
  Ventricular tissues and isolated myocytes were obtained from mice with targeted deletion of either Gα(i2) (Gα(i2) (-/-)) or Gα(i3) (Gα(i3) (-/-)). mRNA levels of Gα(i/o) isoforms and L-VDCC subunits were quantified by real-time PCR. Gα(i) and Ca(v)α(1) protein levels as well as protein kinase B/Akt and extracellular signal-regulated kinases 1/2 (ERK1/2) phosphorylation levels were assessed by immunoblot analysis. L-VDCC function was assessed by whole-cell and single-channel current recordings.
  
  
  RESULTS
  In cardiac tissue from Gα(i2) (-/-) mice, Gα(i3) mRNA and protein expression was upregulated to 187 ± 21% and 567 ± 59%, respectively. In Gα(i3) (-/-) mouse hearts, Gα(i2) mRNA (127 ± 5%) and protein (131 ± 10%) levels were slightly enhanced. Interestingly, L-VDCC current density in cardiomyocytes from Gα(i2) (-/-) mice was lowered (-7.9 ± 0.6 pA/pF, n = 11, p<0.05) compared to wild-type cells (-10.7 ± 0.5 pA/pF, n = 22), whereas it was increased in myocytes from Gα(i3) (-/-) mice (-14.3 ± 0.8 pA/pF, n = 14, p<0.05). Steady-state inactivation was shifted to negative potentials, and recovery kinetics slowed in the absence of Gα(i2) (but not of Gα(i3)) and following treatment with pertussis toxin in Gα(i3) (-/-). The pore forming Ca(v)α(1) protein level was unchanged in all mouse models analyzed, similar to mRNA levels of Ca(v)α(1) and Ca(v)β(2) subunits. Interestingly, at the cellular signalling level, phosphorylation assays revealed abolished carbachol-triggered activation of ERK1/2 in mice lacking Gα(i2).
  
  
  CONCLUSIONS
  Our data provide novel evidence for an isoform-specific modulation of L-VDCC by Gα(i) proteins. In particular, loss of Gα(i2) is reflected by alterations in channel kinetics and likely involves an impairment of the ERK1/2 signalling pathway.
authors.affiliation: Department of Pharmacology, University of Cologne, Cologne, Germany.
authors.forename: Sara
authors.initials: S
authors.lastname: Dizayee
authors.forename: Sonja
authors.initials: S
authors.lastname: Kaestner
authors.forename: Fabian
authors.initials: F
authors.lastname: Kuck
authors.forename: Peter
authors.initials: P
authors.lastname: Hein
authors.forename: Christoph
authors.initials: C
authors.lastname: Klein
authors.forename: Roland P
authors.initials: RP
authors.lastname: Piekorz
authors.forename: Janos
authors.initials: J
authors.lastname: Meszaros
authors.forename: Jan
authors.initials: J
authors.lastname: Matthes
authors.forename: Lutz
authors.initials: L
authors.lastname: Bjrnbaumer
authors.forename: Bernd
authors.initials: B
authors.lastname: Nürnberg
authors.forename: Stefan
authors.initials: S
authors.lastname: Herzig
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D004195:Disease Models, Animal; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D006333:Heart Failure / Q000378:metabolism; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000378:metabolism*; D037342:Pertussis Toxin / Q000737:chemistry; D010766:Phosphorylation; D020033:Protein Isoforms; D015398:Signal Transduction
chemical_list: D020746:Calcium Channels, L-Type; D020033:Protein Isoforms; D037342:Pertussis Toxin; D048049:Extracellular Signal-Regulated MAP Kinases; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498016:Gnai2 protein, mouse; C417708:Gnai3 protein, mouse