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Introduction: Ouabaine is a well-known atrioventricular (AV) node depressant agent, but its effects on functional properties of the AV node have not been cleared. The aim of the present study was to determine how ouabaine administration modifies the rate-dependent properties of the AV node. Methods: Selective stimulation protocols were used to quantify independently electrophysiological properties of the Node. Ouabaine was added directly to superfusion tyrods in a cumulative model (0.05, 0.1, 0.2, 0.25 μM) . The same stimulation protocols were repeated before and after ouabaine addition. Comparisons among multiple groups were made by two-way analysis of variance. P<0.05 was considered significant. Results: Ouabaine decreased fatigue in low concentration (0.05μM), whereas at high concentrations increased the magnitude of fatigue. Ouabaine (0.2, 0.25 μM) caused significant increase in basic properties of the AV-Node (AVCT, WBCL, ERP, FRP). WBCL was prolonged by ouabaine (0.25 μM) from 147.5 ± 8.9 to 194 ± 13 msec. Also amount of facilitating decreased by 0.2 μM ouabaine from 43.3 ± 5 to 38.8 ± 5 msec. Conclusion: The paradoxical effects of ouabaine on the fatigue indicate potential role of Na+-K+-ATPase in the protective mechanism of the AV-node.

Keywords: Isolated heart, rabbit AV Nod, Ouabaine, Na+-K+ ATPase

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