Effect of electrical field stimulation on spontaneous Ca²⁺ transients in rat pulmonary vein cardiomyocytes (864.4)

Abstract

The pulmonary veins (PVs) are widely recognised as an important source of ectopic electrical activity that can lead to atrial fibrillation. While the ectopic activity most likely originates in the cardiomyocytes that form an external sleeve around the PVs, the underlying mechanism remains to be elucidated. Recently, changes in the intracellular Ca2+ concentration have been proposed to play a role. Studies were carried out on intact PVs isolated from the rat, using fluo‐4 to monitor intracellular Ca2+ within individual cardiomyocytes. Under basal unstimulated conditions, spontaneous Ca2+ transients were observed that were asynchronous in neighbouring cells. The frequency of spontaneous Ca2+ transients increased from 0.45 ± 0.06 Hz to 0.59 ± 0.05 Hz (P<0.001) immediately following electrical field stimulation at 5 Hz. Increasing the external Ca2+ concentration to 4.5 mM enhanced this effect, with the frequency of spontaneous Ca2+ transients increasing from 0.45 ± 0.05 Hz under basal conditions to 0.91 ± 0.07 Hz after electrical stimulation (P<0.001). Thus, although electrical field stimulation significantly increased the frequency of the spontaneous Ca2+ transients, their asynchronous nature would mean that they are unlikely to be capable of triggering an action potential. Other interventions that could lead to entrainment of the Ca2+ transients are currently being investigated.