The pulmonary vein is surrounded by an external sleeve of cardiomyocytes that are widely recognised to play an important role in atrial fibrillation. While intracellular Ca2+ is thought to influence the electrical activity of cardiomyocytes, there have been relatively few studies examining Ca2+ signalling in these cells. Therefore, using fluo-4 and fluorescence imaging microscopy, we have investigated Ca2+ signalling in an intact section of the rat pulmonary vein. Under resting conditions cardiomyocytes displayed spontaneous Ca2+ transients, which were variable in amplitude and had a frequency of 1.6±0.03 Hz. The Ca2+ transients were asynchronous amongst neighbouring cardiomyocytes and tended to propagate throughout the cell as a wave. Removing extracellular Ca2+ produced a slight reduction in the amplitude and frequency of the spontaneous Ca2+ transients; however, ryanodine (20M) had a much greater effect on the amplitude and reduced the frequency by 94±2%. Blocking IP3 receptors with 2-aminoethoxydiphenyl borate (20M) also reduced the amplitude and frequency (by 73±11%) of these events, indicating the importance of Ca2+ release from the SR. Electrical field stimulation of the pulmonary vein produced Ca2+ transients in cardiomyocytes that were significantly reduced by either voltage-gated Ca2+ channel blockers or ryanodine.
- pulmonary vein
- cell calcium