效应:末梢释放去甲肾上腺素( norepinephrine),作用 于心肌细胞膜上β受体,引起cAMP增加,导致: 1.窦房结自律性加强,心率加快(Ir增加) 正性变时作用( positive chronotropic action 0 -80 100 msec 0 TP-2 a Fig. 22-20 Mechanisms involved in the changes in fre quency of pacemaker firing. In A, a reduction in the slope(from re17-13 The transmembrane potential changes(A)that occur in SA a to b) of slow diastolic depolarization diminishes the firing fre (owe).(Redraw frum Brown HE Physiol Rev 61: 644, 1981)效应: 末梢释放去甲肾上腺素（norepinephrine),作用 于心肌细胞膜上 受体,引起cAMP增加，导致: 1.窦房结自律性加强,心率加快（If 增加） 正性变时作用（positive chronotropic action)