INVESTIGATION THE EFFECTS OF UL-FS49 AND ZD7288 ON THE INTACT SINO-ATRIAL NODE

The sino-atrial (SA) node is not a homogeneous tissue in terms of its structure and electrophysiological function. The regional differences in action potential configuration is well known. One reason for those differences is the differences on ionic currents underlying the regional differences in electrical activity. One of the currents thought to play an important role in SA node for pacemaker slope of action potential should be hyperpolarization–activated current if. In the present study the conventional glass microelectrode was used for intracellular recording. The if current was separately blocked by 1µM UL-FS49 for 90 min and 3µM ZD7288 for 40 min. The action potentials from different regions of intact SA node were recorded before and during using blockers. UL-FS49 significantly (P<0.05) decreased the pacemaker slope (PS) to 66 ± 5% in peripheral (n=5) and to 23 ± 6% in central (n=5) zones. UL-FS49 also significantly (P<0.05) decreased the rate of spontaneous activity to 16 ± 3% (n=10). ZD7288 completely abolished the pacemaker slope (PS) in peripheral (n=5) and to 22 ± 5 % in central (n=5) zones. ZD7288 also significantly (P<0.05) decreased the rate of spontaneous activity to 13 ± 3% (n=10). Base on the our results, it is possible to conclude that if current plays a major role in pacemaker activity in the periphery and a minor role in pacemaker activity in the center of intact SA node of rabbit heart.