Merriam Laura A, Barstow Karen L, Parsons Rodney L
Department of Anatomy and Neurobiology, University of Vermont, 89 Beaumont Avenue, Given C427, Burlington, VT 05405, USA.
Regul Pept. 2004 Dec 15;123(1-3):123-33. doi: 10.1016/j.regpep.2004.04.019.
Pituitary adenylate cyclase-activating polypeptide (PACAP) peptides, which are co-localized with acetylcholine in preganglionic parasympathetic fibers innervating guinea pig intracardiac ganglia, depolarize and increase excitability of intracardiac neurons. Perforated patch whole cell recordings were used to test whether PACAP27-enhanced activation of Ih contributed to the increase in excitability. In current clamp, 100 nM PACAP27 increased rectification during 500-ms hyperpolarizations and increased the number of anodal break action potentials (APs). PACAP27 also increased the number of APs produced by 500-ms depolarizing currents. In voltage clamp, the effects of 100 nM PACAP27 were determined during hyperpolarizing steps from -50 mV to voltages between -60 and -120 mV. PACAP27 increased the amplitude and rate of activation of Ih. PACAP27 shifted the voltage dependence of activation of Ih by 6.6 mV. The effect of PACAP27 was eliminated by pretreatment with the Ih inhibitor ZD7288 (100 microM). The adenylyl cyclase activator forskolin (10 microM) produced a similar shift in the voltage dependence of Ih activation. We conclude that PACAP27 enhances Ih by shifting the voltage dependence of activation and propose that this effect is mediated primarily by PAC1 receptor activation of adenylyl cyclase and generation of cAMP. Furthermore, we propose that the peptide-enhanced Ih contributes to the PACAP27-induced increase in membrane excitability.
垂体腺苷酸环化酶激活多肽（PACAP）肽与乙酰胆碱共同定位于支配豚鼠心内神经节的节前副交感神经纤维中，可使心内神经元去极化并增加其兴奋性。采用穿孔膜片全细胞记录法来检测PACAP27增强的Ih激活是否导致了兴奋性增加。在电流钳记录中，100 nM PACAP27增加了500毫秒超极化期间的整流作用，并增加了阳极断裂动作电位（AP）的数量。PACAP27还增加了由500毫秒去极化电流产生的AP数量。在电压钳记录中，在从 -50 mV到 -60至 -120 mV之间电压的超极化步骤期间测定100 nM PACAP27的作用。PACAP27增加了Ih的激活幅度和速率。PACAP27使Ih激活的电压依赖性向正电位方向移动了6.6 mV。Ih抑制剂ZD7288（100 microM）预处理可消除PACAP27的作用。腺苷酸环化酶激活剂毛喉素（10 microM）使Ih激活的电压依赖性产生了类似的移动。我们得出结论，PACAP27通过改变激活的电压依赖性来增强Ih，并提出这种作用主要由PAC1受体激活腺苷酸环化酶和生成cAMP介导。此外，我们提出该肽增强的Ih促成了PACAP27诱导的膜兴奋性增加。
