Brown A M, Kunze D L, Yatani A
J Physiol. 1986 Oct;379:495-514. doi: 10.1113/jphysiol.1986.sp016266.
We studied the effects of dihydropyridine Ca channel ligands (DHPs), mainly nitrendipine and Bay K8644, on whole cell and single channel Ca currents on single myocytes isolated from the adult guinea-pig ventricle. Nitrendipine had dual effects, stimulatory or inhibitory, depending upon the membrane potential. At low frequencies (less than 0.03 Hz) and negative holding potentials (-90 mV or more), nitrendipine increased the Ca currents in a dose-dependent manner. The dose-response curve was best fitted by a Langmuir adsorption isotherm model which was the sum of two independent one-to-one drug-receptor sites with median effective doses (ED50S) of 1.0 X 10(-9) M and 1.4 X 10(-6) M respectively. When the membrane potential was held at -30 mV or less, nitrendipine inhibited the Ca currents, also in a dose-dependent manner. The dose-response curve was fitted by a single binding site model having a median inhibitor concentration (IC50) of 1.5 X 10(-9) M. At holding potentials between -70 and -40 mV, nitrendipine produced mixed effects on Ca currents; an increase occurred initially and this was followed by a decrease. When rundown was excluded, Bay K8644 showed only stimulatory effects on the Ca currents between holding potentials of -120 and -30 mV. When the test potential was zero or +10 mV the Ca currents reached peak values and the dose-response curve was best fitted by a single binding site model having an ED50 of 3 X 10(-8) M. When the effects were measured at negative test potentials of -30 to -10 mV, the curve was best fitted by a two-site model with ED50S of 3 X 10(-9) and 9 X 10(-7) M. At the single Ca channel level the stimulatory effect of nitrendipine was due to an increased probability that a Ca channel which had opened once would reopen, a reduction in records without activity and an increase in the mean open time. There were no changes in unit conductance. Inhibitory effects were due to a large increase in nulls. At lower concentrations the main effect of Bay K8644 was an increase in the probability of opening. At doses above 10(-6) M, a pronounced increase in the open time was observed. The effects we observed are attributed to at least two sites for DHP related to Ca channels; one with high affinity and one with a lower affinity. The low affinity site mediates a stimulatory effect due to greatly prolonged openings.(ABSTRACT TRUNCATED AT 400 WORDS)
我们研究了二氢吡啶类钙通道配体（DHPs），主要是尼群地平和Bay K8644，对从成年豚鼠心室分离的单个心肌细胞的全细胞和单通道钙电流的影响。尼群地平具有双重作用，刺激或抑制作用，这取决于膜电位。在低频（小于0.03 Hz）和负的保持电位（-90 mV或更低）时，尼群地平以剂量依赖性方式增加钙电流。剂量反应曲线最好用Langmuir吸附等温线模型拟合，该模型是两个独立的一对一药物-受体位点的总和，其半数有效剂量（ED50）分别为1.0×10（-9）M和1.4×10（-6）M。当膜电位保持在-30 mV或更低时，尼群地平也以剂量依赖性方式抑制钙电流。剂量反应曲线用具有半数抑制浓度（IC50）为1.5×10（-9）M的单一结合位点模型拟合。在-70至-40 mV的保持电位下，尼群地平对钙电流产生混合效应；最初出现增加，随后出现减少。当排除电流衰减时，Bay K8644在-120至-30 mV的保持电位之间对钙电流仅表现出刺激作用。当测试电位为零或+10 mV时，钙电流达到峰值，剂量反应曲线最好用具有ED50为3×10（-8）M的单一结合位点模型拟合。当在-30至-10 mV的负测试电位下测量效应时，曲线最好用具有ED50分别为3×10（-9）和9×10（-7）M的双位点模型拟合。在单个钙通道水平上，尼群地平的刺激作用是由于曾经打开过一次的钙通道再次打开的概率增加、无活性记录的减少以及平均开放时间的增加。单位电导没有变化。抑制作用是由于零电流大幅增加。在较低浓度下，Bay K8644的主要作用是增加开放概率。在剂量高于10（-6）M时，观察到开放时间明显增加。我们观察到的效应归因于与钙通道相关的至少两个DHP位点；一个具有高亲和力，一个具有较低亲和力。低亲和力位点由于开放时间大大延长而介导刺激作用。（摘要截短至400字）
