Studies on the Automatism (I)

Pacemaker cells of the isolated sinus node of the guinea pig were exposed to K-free, Acetylcholine, 2-4-Dinitrophenol, cyclic AMP and Ca-free Krebs solution.Potentials were recorded by means of a conventional microelectrode technique. The sinus node tissue closed to the crista terminalis was trimmed to 1 × 0.5mm area including the dominant pacemaker cells. The tissue was transported into a bath of 1.0ml capacity filled with the standard Kreds solution saturated with a gas mixture of 95%O2 and 5%CO2.1) When the pacemaker cells were perfused in the K-free Krebs solution, they showed an after-oscillatory potential.2) When the cells were perfused in the Ach solution, they had no oscillatory potential before and after that of the pacemaker potential.3) In the 2-4-Dinitrophenol solution, they had a pre-oscillatory potential only before the disappearance and not after the recovery of the pacemaker potential.4) If the cells were perfused in the cAMP solution, they showed a pre-oscillatory potential just before the disappearance and immediately after the recovery of the pacemaker potential.In conclusion these oscillations were enhanced by the K-deficiency and the increase of the membrane resistance and were depressed by the Ca-deficiency. Results suggest that the inward Ca-current plays an important role in the oscillatory potential when the function of electrogenic pump was decreased.