Galpha(i2) but not Galpha(i3) is required for muscarinic inhibition of contractility and calcium currents in adult cardiomyocytes.
Parasympathetic stimulation of the heart acts through M(2)-muscarinic acetylcholine receptors to regulate ion channel activity and subsequent inotropic status. Although muscarinic signal transduction is mediated via pertussis toxin-sensitive G proteins Galpha(i/o), the specific signal transduction requirements of Galpha(i2) and Galpha(i3) in mediating muscarinic regulated L-type calcium currents (I(Ca, L)), intracellular calcium, and cell contractility remain to be determined. Adult ventricular myocytes were isolated from Galpha(i2)-null mice, Galpha(i3)-null mice, and their wild-type littermates. Cell shortening, intracellular calcium levels, and I(Ca, L) were all measured in response to isoproterenol, a beta-adrenergic receptor agonist, and carbachol, a cholinergic receptor agonist. With isoproterenol stimulation, myocytes from all groups demonstrated a marked increase in calcium currents, correlating with augmented intracellular calcium transient amplitude and cell shortening. Carbachol significantly attenuated the isoproterenol response in wild-type and Galpha(i3)-null cells but had no effect in Galpha(i2)-null cells. This study demonstrates that Galpha(i2), but not Galpha(i3), is required for muscarinic inhibition of the beta-adrenergic response in adult murine ventricular myocytes.
Nagata
K
K
Whitaker Cardiovascular Institute, Cardiac Muscle Research Laboratory, Boston University School of Medicine, Boston, Massachusetts, USA.
Ye
C
C
Jain
M
M
Milstone
D S
DS
Liao
R
R
Mortensen
R M
RM
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism*; D018390:Gene Targeting; D006329:Heart Conduction System / Q000187:drug effects / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects* / Q000235:genetics; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects
D000318:Adrenergic beta-Agonists; D020746:Calcium Channels, L-Type; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011518:Proto-Oncogene Proteins; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; D002217:Carbachol; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498016:Gnai2 protein, mouse; D020962:Heterotrimeric GTP-Binding Proteins; D007545:Isoproterenol; D002118:Calcium