Expression of a Gi-coupled receptor in the heart causes impaired Ca2+ handling, myofilament injury, and dilated cardiomyopathy.
Increased signaling by G(i)-coupled receptors has been implicated in dilated cardiomyopathy. To investigate the mechanisms, we used transgenic mice that develop dilated cardiomyopathy after conditional expression of a cardiac-targeted G(i)-coupled receptor (Ro1). Activation of G(i) signaling by the Ro1 agonist spiradoline caused decreased cellular cAMP levels and bradycardia in Langendorff-perfused hearts. However, acute termination of Ro1 signaling with the antagonist nor-binaltorphimine did not reverse the Ro1-induced contractile dysfunction, indicating that Ro1 cardiomyopathy was not due to acute effects of receptor signaling. Early after initiation of Ro1 expression, there was a 40% reduction in the abundance of the sarcoplasmic reticulum Ca(2+)-ATPase (P < 0.05); thereafter, there was progressive impairment of both Ca(2+) handling and force development assessed with ventricular trabeculae. Six weeks after initiation of Ro1 expression, systolic Ca(2+) concentration was reduced to 0.61 +/- 0.08 vs. 0.91 +/- 0.07 microM for control (n = 6-8; P < 0.05), diastolic Ca(2+) concentration was elevated to 0.41 +/- 0.07 vs. 0.23 +/- 0.06 microM for control (n = 6-8; P < 0.01), and the decline phase of the Ca(2+) transient (time from peak to 50% decline) was slowed to 0.25 +/- 0.02 s vs. 0.13 +/- 0.02 s for control (n = 6-8; P < 0.01). Early after initiation of Ro1 expression, there was a ninefold elevation of matrix metalloproteinase-2 (P < 0.01), which is known to cause myofilament injury. Consistent with this, 6 wk after initiation of Ro1 expression, Ca(2+)-saturated myofilament force in skinned trabeculae was reduced to 21 +/- 2 vs. 38 +/- 0.1 mN/mm(2) for controls (n = 3; P < 0.01). Furthermore, electron micrographs revealed extensive myofilament damage. These findings may have implications for some forms of human heart failure in which increased activity of G(i)-coupled receptors leads to impaired Ca(2+) handling and myofilament injury, contributing to impaired ventricular pump function and heart failure.
McCloskey
Diana T
DT
VA Medical Center, Cardiology Division (111C ), University of California-San Francisco, 4150 Clement St., San Francisco, CA 94121, USA.
Turcato
Sally
S
Wang
Guan-Ying
GY
Turnbull
Lynne
L
Zhu
Bo-Qing
BQ
Bambino
Thomas
T
Nguyen
Anita P
AP
Lovett
David H
DH
Nissenson
Robert A
RA
Karliner
Joel S
JS
Baker
Anthony J
AJ
D008841:Actin Cytoskeleton / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002311:Cardiomyopathy, Dilated / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D016277:Ventricular Function, Left
D009292:Narcotic Antagonists; D011759:Pyrrolidines; D043562:Receptors, G-Protein-Coupled; D017473:Receptors, Opioid, kappa; C051844:norbinaltorphimine; D009271:Naltrexone; D000242:Cyclic AMP; D020778:Matrix Metalloproteinase 2; C522362:Mmp2 protein, mouse; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C051272:spiradoline; D002118:Calcium