2019 Volume 27 Pages 1-12
The cellular morphology and spatio-temporal pattern of the rise in Ca2+ during the early-phase Ca2+ transients of isolated guinea pig pulmonary vein cardiomyocytes were studied using confocal microscopy and compared with those of ventricular and atrial cardiomyocytes. The pulmonary vein cardiomyocytes had cross striations and were rich in sarcoplasmic reticulum but lacked T-tubules; this was similar to atrial cardiomyocytes but different from ventricular cardiomyocytes, in which T-tubules were present throughout the cell. The sarcoplasmic reticulum was present throughout the cytoplasm in all cell types. On the induction of Ca2+ transients by electrical field stimulation of the pulmonary vein cardiomyocytes, the rise in Ca2+ concentration first occurred at the subsarcolemmal region and then spread to the cell interior; this phenomenon was similar to that in atrial cardiomyocytes but different from that in ventricular cardiomyocytes, in which the Ca2+ concentration rose simultaneously throughout the cytoplasm. The properties of the Ca2+ sparks and Ca2+ waves in the pulmonary vein cardiomyocytes were the same as those in atrial and ventricular cardiomyocytes. In pulmonary vein cardiomyocytes showing spontaneous activity, the Ca2+ transients were preceded by increased firing of Ca2+ sparks. These results indicate that, in guinea pig pulmonary vein cardiomyocytes that lack T-tubules, Ca2+ transients involve the propagation of Ca2+ waves, which is similar to that of atrial but not ventricular cardiomyocytes. Ca2+ sparks appear to be involved in the generation of spontaneous Ca2+ transients of pulmonary vein cardiomyocytes.