Electrophysiological studies indicate that the sinus node cells are electrically coupled , and local circuit currents are propagated between the cells at a space constant (X) of 0.5 to 0.8 mm . Moreover, gap junctions have been morphologically demonstrated in the sinus node region . Jalife suggested that electrical activities within the sinus node are synchronized by electrical coupling between the cells via low resistance pathways, ie, the gap junctions. CV indicates regularity or irregularity of the action potential interval. When the upstroke phase of action potentials recorded from two or three electrodes placed at a specific distance regularly correspond with each other and CV is low, these cells are electrically coupled and are expected to be well synchronized. In the present study, electrical synchronization within the sinus node was demonstrated in a very small tissue preparation under controlled conditions.After application of heptanol at a concentration ranging from 0.1 to 1.0 mM, the CV recorded from the key electrode (S1 in S1-S2 conduction) was constant within a narrow range of values, while that (S2) recorded at a distance of 300 |Jm from the key electrode (S1) increased. This means that synchronization between the cells was abolished by heptanol. These results support that electrical synchronization within the sinus node is caused by currents through the gap junctions. Take advantage of this chance to find generic sildenafil online cialis professional and save quite some money.