[Effect of atrial natriuretic factor on the automaticity of sinus node in guinea pig heart]

The effect of atrial natriuretic factor (ANF) on sinoatrial (SA) node cells in guinea pig heart was studied by using intracellular microelectrodes. When the heart superfused with ANF 0.025 and 0.05 mumol/L for 7 min respectively, the spontaneous rate showed no significant changes, but 0.1 mumol/L ANF resulted in a definite decrease by 7% (P less than 0.01). However, when ANF (0.025, 0.05 and 0.1 mumol/L) was superfused along with 0.5 mumol/L isoproterenol, the spontaneous rate was respectively depressed by 4, 12 and 22%. These results indicate that ANF can depress the positive chronotropic effect of isoproterenol. The mechanism of this action may be related to the blocking effect of ANF on T-type calcium channel of SA node.