Chronic receptor-mediated activation of Gi/o proteins alters basal t-tubular and sarcolemmal L-type Ca²⁺ channel activity through phosphatases in heart failure.
L-type Ca(2+) channels (LTCCs) play an essential role in the excitation-contraction coupling of ventricular myocytes. We previously found that t-tubular (TT) LTCC current density was halved by the activation of protein phosphatase (PP)1 and/or PP2A, whereas surface sarcolemmal (SS) LTCC current density was increased by the inhibition of PP1 and/or PP2A activity in failing ventricular myocytes of mice chronically treated with isoproterenol (ISO mice). In the present study, we examined the possible involvement of inhibitory heterotrimeric G proteins (G(i/o)) in these abnormalities by chronically administrating pertussis toxin (PTX) to ISO mice (ISO + PTX mice). Compared with ISO mice, ISO + PTX mice exhibited significantly higher fractional shortening of the left ventricle. The expression level of Gα(i2) proteins was not altered by the treatment of mice with ISO and/or PTX. ISO + PTX myocytes had normal TT and SS LTCC current densities because they had higher and lower availability and/or open probability of TT and SS LTCCs than ISO myocytes, respectively. A selective PKA inhibitor, H-89, did not affect LTCC current densities in ISO + PTX myocytes. A selective PP2A inhibitor, fostriecin, did not affect SS or TT current density in control or ISO + PTX myocytes but significantly increased TT but not SS LTCC current density in ISO myocytes. These results indicate that chronic receptor-mediated activation of G(i/o) in vivo decreases basal TT LTCC activity by activating PP2A and increases basal SS LTCC activity by inhibiting PP1 without modulating PKA in heart failure.
Department of Molecular Pharmacology, Shinshu University School of Medicine, Nagano, Japan.
Toshihide
T
Kashihara
Tsutomu
T
Nakada
Hisashi
H
Shimojo
Miwa
M
Horiuchi-Hirose
Simmon
S
Gomi
Toshihide
T
Shibazaki
Xiaona
X
Sheng
Masamichi
M
Hirose
Minoru
M
Hongo
Mitsuhiko
M
Yamada
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000465:Algorithms; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects / Q000502:physiology*; D006333:Heart Failure / Q000000981:diagnostic imaging / Q000201:enzymology*; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D009206:Myocardium / Q000473:pathology; D032383:Myocytes, Cardiac / Q000502:physiology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D014463:Ultrasonography
D000318:Adrenergic beta-Agonists; D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D043562:Receptors, G-Protein-Coupled; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D007545:Isoproterenol