Serum Positive for the Autoantibody against the β (1)-Adrenoceptor from Chinese Patients with Congestive Heart Failure Decreases I (ss) in Mouse Cardiac Myocytes

Autoantibodies targeting the β (1)-adrenergic receptor (AAB-β (1)) display agonist-like effects, which may have a pathogenic role in the progression of heart failure. Here, we used the electrophysiological recordings to explore the effects of AAB-β (1)-positive serum from Chinese patients with heart failure on the activity of the peak transient outward potassium current (I (to)) and the end 50 ms steady-state potassium current (I (ss)) in mouse cardiac myocytes. We found that the AAB-β (1)-positive serum had no effect on the activity of I (to), but it produced a decrease in the currents of I (ss). A low concentration of positive serum (1/100) had a small inhibitory effect on I (ss). However, positive serum at 1 : 10, 1 : 20, and 1 : 50 significantly decreased I (ss). The concentration-dependence analysis showed that the EC(50) of AAB-β (1)-positive serum was 1/60.24 and its nH was 2.86. It indicated that the AAB-β (1) could inhibit I (ss) in mouse cardiomyocyte in a concentration-dependent manner.