Rapid Electrical Stimulation of Contraction Reduces the Density of β-Adrenergic Receptors and Responsiveness of Cultured Neonatal Rat Cardiomyocytes

Abstract

Background-Although tachycardia is commonly present in patients with congestive heart failure, its role in the development of congestive heart failure remains unclear. We studied the effect of rapid electrical stimulation of contraction on ␤-adrenergic receptor (␤-AR) signal pathway in cultured cardiomyocytes of neonatal rats. Methods and Results-Contraction of cardiomyocytes was induced by electrical stimulation at 50 V with twice the threshold pulse width. ␤-ARs were identified by [ 3 H]CGP-12177 and [ 3 H]dihydroalprenolol. Electrical stimulation reduced cell-surface but not total ␤-AR density; the effect was dependent on pacing frequency (a reduction of 11%, 28%, and 18% in cells paced at 2.5, 3.0, and 3.3 Hz, respectively). This reduction was apparent at 3 hours, in contrast to reduced ␤-AR density after exposure to isoproterenol (ISP) for 1 hour. The fraction and inhibition constant of ␤-AR binding agonist with high affinity were not affected by rapid electrical stimulation. In cardiomyocytes paced at 3.0 Hz for 24 hours, the response to ISP decreased compared with unpaced cells, 142% versus 204% of baseline with 1 mol/L ISP, whereas the responses to forskolin or acetylcholine were not different. Treatment of cardiomyocytes with 2,3-butanedione monoxime (10 mmol/L) or taxol (10 mol/L) inhibited the rapid pacing-induced reduction in ␤-AR density. Conclusions-Our results suggest that contractile activity is involved in regulation of cardiac function by modulating the ␤-AR system independently of hemodynamic and neurohormonal factors. This may help to elucidate the role of mechanical stress in the development of heart failure.

Impaired left and right ventricular function following prolonged exercise in young athletes: influence of exercise intensity and responses to dobutamine stress

“…Data from animal chronic pacing studies (i.e., duration: 3 h to 20 days) have demonstrated significant reductions in ventricular function (1, 25, 44), secondary to reductions in ␤-adrenergic sensitivity and density (31, 35, 44). A reduction in ␤-adrener- gic receptor density has been demonstrated following an acute 3-h cardiomyocyte pacing model (44). A similar mechanism of action specific to ␤-adrenergic sensitivity density (22) may be active during higher intensity PE.…”

Inhibition of β-adrenergic receptor trafficking in adult cardiocytes by MAP4 decoration of microtubules

“…In now taking this question to the heart, we have focused on the G protein-coupled adrenergic receptor, because it is well established that ␤-AR responsiveness is reduced due to ␤-AR desensitization and downregulation both in patients with cardiac hypertrophy and failure and in animal models of these conditions (1,8,10,14,21,28,35). In parallel, increased concentrations of tubulin and MAP4, with MAP4 decoration of microtubules, are found in the heart as early as 2 days after pressure overloading and persist for at least 6 mo thereafter (25,31).…”

ERK1/2 Regulates Intracellular ATP Levels through α-Enolase Expression in Cardiomyocytes Exposed to Ischemic Hypoxia and Reoxygenation

“…Cell Culture and Ischemic Cell Model-Primary cultures of 1-to 2-day-old neonatal rat ventricular myocytes were prepared as reported previously (32). The cardiomyocytes dissociated enzymatically were seeded on culture trays at a concentration of 3 ϫ 10 5 cells/cm 2 and then incubated in L-15 Medium (Worthington Biochemical Co.) supplemented with 5% fetal bovine serum at 37°C.…”