ИСТИНА

Actions potentials, resting membrane potential instability and automaticity in the rat caval and azygos veins myocardium Introduction Thoracic veins myocardium is capable of generating electrical automatic activity that is considered to be a trigger for initiation and maintenance of atrial fibrillation. Despite the demonstration of cardiac tissue and contractility of the superior vena cava (SVC) and azygos vein (AZV), the electrophysiological properties of SVC and AZV have not yet been described. Purpose The aim of the present study was to investigate the electrical activity of the cardiac tissue in the rat SVC and AZV. Materials and methods Electrically evoked or spontaneous action potentials (AP) and resting membrane potential (RPM) were recorded in multicellular isolated Tirode perfused preparations of left or right atria (LA, RA), SVC or AZV with use of standard microelectrode technique in control conditions and under application of noradrenaline (NA, 10 µM), isoproterenol (ISO, 10 µM) or phenylephrine (PHE, 10 µM). All preparations were dissected from Wistar rats (male, 200-250g). All experiments were approved by local bioethical committee. Results The atrial-like action potentials (AP) were observed in various sites of both rat SVC and AZV under continuous steady-state electrical pacing (CEP). The AP duration (APD) in the isolated paced SVC and AZV were similar to those in LA, but was significantly shorter compared to the RA myocardium. RMP in the SVC and AZV was depolarized under CEP in comparison to the level in atrial myocardium. Unlike to the atrial myocardium the termination of electrical pacing in both SVC and AZV resulted in significant spontaneous positive shift of the RMP. However, no spontaneous AP were observed in quiescent veins preparation without adrenergic stimulation in both veins preparations. NA induced significant additional depolarization, while ISO caused hyperpolarization of the RMP in both quiescent veins preparations. RMP alteration was smaller in SVR compered to AZV. PHE induced depolarization of the RMP in quiescent AZV preparations, but failed to alter RMP in SVC preparations. Spontaneous AP in form of repetitive quasy-periodic bursts were observed in 30% quiescent AZV preparations in response to the NA application. Spontaneous AP were observed in 20% SVC preparations under application of NA, ISO and PHE. Conclusion In conclusion, the electrical activity in SVC and AZV under a regular excitation resembles those in atrial myocardium, rare adrenergic automaticity has been revealed in non-paced cardiac tissue in the rat SVC and AZV despite RMP instability.