Bolger G T, Gengo P, Klockowski R, Luchowski E, Siegel H, Janis R A, Triggle A M, Triggle D J
J Pharmacol Exp Ther. 1983 May;225(2):291-309.
A chemically heterogeneous group of compounds, the Ca++ channel antagonists, which includes verapamil, diltiazem and nifedipine inhibits excitation-contraction coupling in smooth and cardiac muscle by blocking Ca+ entry at a specific class of Ca++ channels. The binding of the nifedipine analog, [3H]nitrendipine, to a microsomal fraction from guinea-pig longitudinal smooth muscle has been characterized. Specific binding was saturable, linear with protein concentration and reversible. The apparent equilibrium dissociation constant was 1.63 +/- 0.06 X 10(-10)M and the maximum site density was 1.13 +/- 0.03 pmol/mg of protein determined from Scatchard analysis of equilibrium binding at 25 degrees C. Inhibition of binding was specific and stereoselective for Ca++ channel antagonist drugs and was unaffected by a variety of receptor active ligands. Correlations between binding and inhibition of mechanical response to methylfurmethide- and K+-stimulation in a series of nifedipine analogs were determined. A 1:1 correlation was found for the K+ tonic response, but for the phasic component of the K+ response and for both components of the methylfurmethide response the antagonists were more active as inhibitors of [3H]nitrendipine binding than as inhibitors of mechanical response. [3H]Nitrendipine binding was sensitive to other Ca++ channel antagonists including verapamil, D-600, diltiazem, flunarizine, lidoflazine and bepridil. Interaction with these agents suggests, consistent with previous reports, that more than one binding site for Ca++ antagonists exists. A variety of inorganic divalent and trivalent cations (Mn++, Co++, Ni++, Pb++, UO2++, Zn++, Cd++, Cu++, Tm+++ and La+++) inhibit specific [3H]nitrendipine binding. The data suggest that [3H]nitrendipine binding in smooth muscle is to a site which mediates the pharmacologic response.
钙通道拮抗剂是一类化学性质各异的化合物，包括维拉帕米、地尔硫䓬和硝苯地平，它们通过阻断特定类型钙通道的钙离子内流来抑制平滑肌和心肌的兴奋 - 收缩偶联。已对硝苯地平类似物[³H]尼群地平与豚鼠纵行平滑肌微粒体部分的结合特性进行了表征。特异性结合具有饱和性，与蛋白质浓度呈线性关系且可逆。在25℃下通过对平衡结合进行Scatchard分析确定，表观平衡解离常数为1.63±0.06×10⁻¹⁰M，最大位点密度为1.13±0.03 pmol/mg蛋白质。结合的抑制对钙通道拮抗剂药物具有特异性和立体选择性，且不受多种受体活性配体的影响。测定了一系列硝苯地平类似物中结合与对甲基呋塞米和钾离子刺激的机械反应抑制之间的相关性。发现钾离子强直反应存在1:1的相关性，但对于钾离子反应的时相成分以及甲基呋塞米反应的两个成分，拮抗剂作为[³H]尼群地平结合抑制剂比作为机械反应抑制剂更具活性。[³H]尼群地平结合对其他钙通道拮抗剂敏感，包括维拉帕米、D - 600、地尔硫䓬、氟桂利嗪、利多氟嗪和苄普地尔。与这些药物的相互作用表明，与先前报道一致，钙拮抗剂存在不止一个结合位点。多种无机二价和三价阳离子（锰离子、钴离子、镍离子、铅离子、二氧化铀离子、锌离子、镉离子、铜离子、铥离子和镧离子）抑制特异性[³H]尼群地平结合。数据表明，平滑肌中[³H]尼群地平的结合位点介导了药理反应。
