Ultrastructural and Functional Remodeling of the Coupling Between Ca2+ Influx and Sarcoplasmic Reticulum Ca2+ Release in Right Atrial Myocytes From Experimental Persistent Atrial Fibrillation

RATIONALE:Persistent atrial fibrillation (AF) has been associated with structural and electric remodeling and 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