Abstract. The pulmonary vein is known as an important source of ectopic beats, initiating frequent paroxysms of atrial fibrillation. We analyzed electrophysiological and pharmacological characteristics of triggered activity elicited in the isolated pulmonary vein from the guinea pig. Immediately after the termination of train stimulation (pacing cycle length of 100 ms), spontaneous activities accompanied with phase-4 depolarization were detected in 43 out of 45 pulmonary vein preparations. Such triggered activities were not observed in the isolated left atrium. The incidence of triggered activity was higher at a shorter pacing cycle length (100 -200 ms), and the coupling interval was shorter at a shorter pacing cycle length. Verapamil (1 μM), ryanodine (0.1 μM), and pilsicainide (10 μM) suppressed the occurrence of triggered activities. The resting membrane potential of the pulmonary vein myocardium was more positive than that of the left atrium. Carbachol (0.3 μM) hyperpolarized the resting membrane potential and completely inhibited the occurrence of triggered activities. These results suggest that the pulmonary veins have more arrhythmogenic features than the left atrium, possibly through lower resting membrane potential. The electrophysiological and pharmacological characteristics of triggered activity elicited in the pulmonary vein myocardium were similar to those previously reported using ventricular tissues.

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The Front Cover shows the conversion of solar energy by photolysis of water to yield molecular hydrogen. The carboxylato‐bridged dinuclear palladium(II) complexes with clamshell geometry, which are regarded as excellent precatalysts for photo‐induced hydrogen production from water, are depicted as particles in a flask. The rainbow arising from light striking water droplets is an image of visible light, which is the major component of sunlight. The present work demonstrates the considerable potential of palladium catalytic species for photocatalytic hydrogen production. More information can be found in the Research Article by T. Kawamoto and co‐workers.

A series of carboxylato-bridged dinuclear palladium(II) complexes with cyclopalladated 2-phenylbenzothiazole ligands were prepared and characterized by elemental analyses, NMR, IR, and UV-vis spectroscopies, cyclic voltammetry, and X-ray crystallography. All the complexes have clamshell structures in which two cyclopalladated 2-phenylbenzothiazole ligands bound to palladium atoms are in the anti-configuration arranging the ligands in opposite orientations from each other. The PdÀ Pd distances of these complexes are shorter than the sum of the van der Waals radii, indicative of the presence of metal-metal bonding interactions. These dinuclear complexes were used as water reduction catalysts in the photocatalytic system for hydrogen evolution and regarded as precatalysts that are converted into highly catalytically active species.