The characteristics of action potential and nonselective cation current of cardiomyocytes in rabbit superior vena cava

As a special focus in initiating and maintaining atrial fibrillation (AF), cardiomyocytes in superior vena cava (SVC) have distinctive electrophysiological characters. In this study, we found that comparing with the right atrial (RA) cardiomyoctyes, the SVC cardiomyoctyes had longer APD(90) at the different basic cycle lengths; the conduction block could be observed on both RA and SVC cardiomyoctyes. A few of SVC cardiomyoctyes showed slow response action potentials with automatic activity and some others showed early afterdepolarization (EAD) spontaneously. Further more, we found that there are nonselective cation current (I-Ns) in both SVC and RA cardiomyocytes. The peak density of I-Ns in SVC cardiomyocytes was smaller than that in RA cardiomyocytes. Removal of extracellular divalent cation and glucose could increase I-Ns in SVC cardiomyocytes. The agonist or the antagonist of I-Ns may increase or decrease APD. To sum up, some SVC cardiomyocytes possess the ability of spontaneous activity; the difference of transmembrane action potentials between SVC and RA cardiomyocytes is partly because of the different density of I-Ns between them; the agonist or the antagonist of I-Ns can increase or decrease APD leading to the enhancement or reduction of EAD genesis in SVC cardiomyocytes. I-Ns in rabbit myocytes is fairly similar to TRPC3 current in electrophysiological property, which might play an important role in the mechanisms of AF.