Related Experiment Videos
Mechanisms of L-type Ca(2+) current downregulation in rat atrial myocytes during heart failure
C Boixel1, W Gonzalez, L Louedec
1INSERM Unité 460, Faculté de Médecine Xavier Bichat, Paris, France.
Insights
Heart failure reduces L-type calcium current (I(Ca)) in atrial cells due to altered cAMP regulation. This leads to increased sensitivity to catecholamines, impacting heart rhythm.
Area of Science:
- Cardiology
- Molecular Biology
- Electrophysiology
Background:
- Downregulation of L-type Ca(2+) current (I(Ca)) contributes to electrical remodeling in diseased atria.
- Heart failure (HF) affects atrial electrophysiology, necessitating investigation into underlying ionic mechanisms.
Purpose of the Study:
- To investigate the mechanisms of I(Ca) downregulation in atrial myocytes from rats with heart failure.
- To explore the role of cAMP-dependent regulation and beta-adrenergic stimulation in HF-induced I(Ca) changes.
Main Methods:
- Whole-cell patch-clamp technique on isolated rat left atrial myocytes.
- Biochemical assays to assess calcium channel subunit quantities and intracellular signaling molecules.
- Pharmacological manipulation using isoproterenol, okadaic acid, 3-isobutyl-1-methyl-xanthine, and atrial natriuretic peptide.
Main Results:
- I(Ca) density was significantly reduced in HF myocytes compared to sham controls.
- HF myocytes exhibited an exaggerated stimulatory response to isoproterenol and increased sensitivity to cAMP.
- Reduced intracellular cAMP and enhanced cyclic GMP extrusion were observed in HF myocytes.
- Calcium channel alpha(1C)-subunit quantities remained unchanged, indicating post-translational regulation.
Conclusions:
- Atrial I(Ca) downregulation in heart failure is primarily due to impaired basal cAMP-dependent regulation.
- Altered signaling pathways lead to increased responsiveness to catecholamines, contributing to electrical remodeling in HF atria.
Abstract:
Downregulation of the L-type Ca(2+) current (I(Ca)) is an important determinant of the electrical remodeling of diseased atria. Using a rat model of heart failure (HF) due to ischemic cardiopathy, we studied I(Ca) in isolated left atrial myocytes with the whole-cell patch-clamp technique and biochemical assays. I(Ca) density was markedly reduced (1.7+/-0.1 pA/pF) compared with sham-operated rats (S) (4.1+/-0.2 pA/pF), but its gating properties were unchanged. Calcium channel alpha(1C)-subunit quantities were not significantly different between S and HF. The beta-adrenergic agonist isoproterenol (1 micromol/L) had far greater stimulatory effects on I(Ca) in HF than in S (2.5- versus 1-fold), thereby suppressing the difference in current density. Dialyzing cells with 100 micromol/L cAMP or pretreating them with the phosphatase inhibitor okadaic acid also increased I(Ca) and suppressed the difference in density between S and HF. Intracellular cAMP content was reduced more in HF than in S. The phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine had a greater effect on I(Ca) in HF than in S (76.0+/-11.2% versus 15.8+/-21.2%), whereas the inhibitory effect of atrial natriuretic peptide on I(Ca) was more important in S than in HF (54.1+/-4.8% versus 24.3+/-8.8%). Cyclic GMP extruded from HF myocytes was enhanced compared with S (55.8+/-8.0 versus 6.2+/-4.0 pmol. mL(-1)). Thus, I(Ca) downregulation in atrial myocytes from rats with heart failure is caused by changes in basal cAMP-dependent regulation of the current and is associated with increased response to catecholamines.