Ultrastructural and Functional Remodeling of the Coupling Between Ca Influx and Sarcoplasmic Reticulum Ca Release in Right Atrial Myocytes From Experimental Persistent Atrial Fibrillation

reduced contractile function. Objective: To unravel mechanisms underlying reduced sarcoplasmic reticulum (SR) Ca release in persistent AF. Methods: We studied cell shortening, membrane currents, and [Ca ]i in right atrial myocytes isolated from sheep with persistent AF (duration 129 39 days, N 16), compared to matched control animals (N 21). T-tubule density, ryanodine receptor (RyR) distribution, and local [Ca ]i transients were examined in confocal imaging. Results: Myocyte shortening and underlying [Ca ]i transients were profoundly reduced in AF (by 54.8% and 62%, P<0.01). This reduced cell shortening could be corrected by increasing [Ca ]i. SR Ca 2 content was not different. Calculated fractional SR Ca release was reduced in AF (by 20.6%, P<0.05). Peak Ca current