title: Down-regulation of sodium current in chronic heart failure: effect of long-term therapy with carvedilol.
abstract: Evidence has accumulated recently about the importance of alterations in Na+ channel function and slow myocardial conduction for arrhythmias in the infarcted and failing heart. The present study tested a hypothesis that Na+ current (INa/C) density decreases in chronic heart failure (HF) and that Na+ channel (NaCh) functional density can be restored by long-term therapy with carvedilol, a mixed alpha- and beta-adrenergic blocker. Studies were performed using a canine model of chronic HF produced in dogs by sequential intracoronary embolizations with microspheres. HF developed approximately 3 months after the last embolization (left ventricle, LV, ejection fraction = 28 +/- 1%). Ventricular cardiomyocytes (VCs) were isolated enzymatically from LV mid-myocardium, and INa was measured by whole-cell patch-clamp. The maximum INa/C was decreased in failing (n = 19) compared to normal (n = 12) hearts (33.1 +/- 1.6 vs 48.5 +/- 5.1 pA/pF, mean +/- SE, p < 0.001). The steady-state inactivation and activation of INa remained unchanged in failing compared to normal hearts. Long-term treatment with carvedilol (1 mg/kg, twice daily for 3 months) normalized INa/C in dogs with HF. INa/C in HF dogs (n = 6) treated with carvedilol was higher compared to that of non-treated HF dogs (n = 6) (49.4 +/- 0.9 vs 29 +/- 4.8 pA/pF, p < 0.007). In vitro culture of VCs of failing hearts for 24 h did not restore INa/C. However, INa/C was partially restored when VCs were incubated for 24 h with BAPTA-AM, an intracellular Ca2+ buffer. Thus, we conclude that experimental chronic HF in dogs results in down-regulation of the functional density of NaCh that can be restored by long-term therapy with carvedilol. The mechanism of NaCh down-regulation in HF may be linked to poor Ca2+ handling in this stage of disease.
authors.affiliation: Henry Ford Hospital, Cardiovascular Research, Education & Research, Detroit, Michigan 48202-2689, USA.
authors.forename: V A
authors.initials: VA
authors.lastname: Maltsev
authors.forename: H N
authors.initials: HN
authors.lastname: Sabbab
authors.forename: A I
authors.initials: AI
authors.lastname: Undrovinas
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000627:therapeutic use*; D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002227:Carbazoles / Q000627:therapeutic use*; D002303:Cardiac Output, Low / Q000188:drug therapy* / Q000378:metabolism; D000077261:Carvedilol; D002908:Chronic Disease; D004285:Dogs; D015536:Down-Regulation; D009206:Myocardium / Q000166:cytology; D018408:Patch-Clamp Techniques; D011412:Propanolamines / Q000627:therapeutic use*; D015222:Sodium Channels / Q000378:metabolism*
chemical_list: D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D002227:Carbazoles; D011412:Propanolamines; D015222:Sodium Channels; D000077261:Carvedilol; D002118:Calcium