Regional differences in the role of if current in pacemaker potential within the small balls of tissues of sino-atrial (SA) node

The sinoatrial (SA) node is not a homogeneous tissue in terms of its structure and electrophysiological function. The regional differences in action potential configuration are well known. One reason for those differences is the differences on ionic currents underlying the regional differences in electrical activity. One of the ionic currents it is thought to play a role in SA node for pacemaker slope of action potential should be hyperpolarization – activated current if. This prediction was tested in the present study by blocking of this current on pacemaker activity in the small balls of tissue of the rabbit heart. Firstly, the intracellular electrical activity was recorded by glass microelectrode from small balls of tissue from peripheral (ball A) transitional (ball B) and central (balls C and D) zones of the SA node and secondly, the current was block by 2mM Cs+ for 2 min followed by recording electrical activity. In all cases Cs+ significantly decreased the pacemaker slope (PS) to 475 % in ball A (n=5) and to 219 % in ball D (n=4). 2mM Cs+ also decreased the rate of spontaneous activity to 71 % in ball D (n=4) and 191 in ball A (n=5). Base on the results, it is possible to conclude that if current play the major role in pacemaker activity in the center and a minor role in pacemaker activity in the periphery in small balls of tissues of SA node.