烟酰胺对家兔窦房结细胞动作电位的影响及其机制探讨

在离体家兔窦房结标本上,应用微电极技术,观察到NIC(4000 mg/L)使窦房结细胞动作电位的SP₄平均增加62%(P<0.01);SCL平均减少27%(P<0.01);APD₉₀平均减少12%(P<0.05);APA,SP₀无显著变化。VER(0.1 mg/L)可完全阻断NIC的作用,但对ISO(0.03mg/L)的作用无明显影响;PRO(0.25 mg/L)可完全阻断ISO的作用,但NIC的作用不受影响。实验结果提示,NIC可能是一个钙通道激活剂,通过促进i_si而增加窦性频率。

EFFECT OF NICOTINAMIDE ON RABBIT SINUS NODE CELL ACTION POTENTIAL AND ANALYSIS OF ITS MECHANISM

The effects of nicotinamide on isolated rabbit S-A node were studied with standard microelectrode techniques. At a concentration of 4 mg/ml of nicotinamide, the slope of phase 4 of the S-A node cell action potential was significantly increased, the spontaneous sinus cycle length and action potential duration at 90% repolarization were markedly shortened. The rate of depolarization of phase O and the action potential amplitude were unchanged. These effects of nicotinamide were similar to those of isoproterenol (at a concentration of 0.03 mg/L). The effect of nicotinamide could be blocked by verapamil at a concentration of 0.1 mg/L which has no significant effect on the action of isoproterenol. Propranolol at a concentration of 0.25 rag/L, which blocked the effect of isoproterenol completely, showed no effect on the action of nicotinamide. In the experiment, nicotinamide can prevent the slope of phase 4 from being decreased and the sinus spontaneous cycle length from being prolonged by the action of verapamil, but the action of verapamil to decrease the slope of phase O and the amplitude of action potential was not affected. The results suggest that nicotinamide might be an activator of Ca⁽⁺⁺⁾ channel. Nicotinamide could promote the Ca⁺⁺ inward current of phase 4.