Dynamic Changes of Calcium in Sarcoplasmic Reticulum of Rabbit Atrial Myocytes

With each contraction in atrial muscle, Ca2+ is released from the sarcoplasmic reticulum (SR) through ryanodine receptors and then reaccumulated by the activity of the SR Ca2+ ATPase (SERCA). Recent experiments by us and others have examined SR Ca2+ concentration ([Ca2+]SR) using low affinity fluorescent Ca2+ sensors (e.g. fluo-5N) in ventricular myocytes (Brochet et al. PNAS 2005 102(8) 3099-104) however, similar characterization in atrial cells is missing. Here we examine [Ca2+] SR dynamics in healthy adult rabbit atrial myocytes using fluo-5N. Fractional SR Ca2+release at room temperature was 30% (n=12), where caffeine was used to determine 100% release. Restoration of [Ca2+]SR by SERCA was consistent with the decline of [Ca2+]i with each beat (1 Hz). The interconnectivity of the cell-wide SR and nuclear envelope and endoplasmic reticulum was characterized using fluorescence recovery after photobleaching (FRAP). Additional diverse modulations of atrial cell [Ca2+]SR will be discussed.View Large Image | View Hi-Res Image | Download PowerPoint Slide