Bellemann P
J Recept Res. 1984;4(1-6):571-85. doi: 10.3109/10799898409042574.
Binding properties of the calcium channel activating dihydropyridine (DHP), H-BAY K 8644, and the inhibiting 3H-verapamil were demonstrated in monolayer cultures of beating cardiac cells. 3H-BAY K 8644 specific binding was dependent on the presence of extracellular calcium, the affinity was modulated by Ca2+, but Hill coefficients remained unaffected. BAY K 8644 stimulated myocardial contractility in resting and beating myocytes. In contrast to beta-adrenoceptor agonists, however, cellular levels of cyclic AMP and cyclic GMP in cultured myocytes remained unchanged by the compound. Dihydropyridine derivatives of both the calcium channel activating BAY K 8644 as well as the Ca2+ entry blocking DHPs of the nifedipine or nimodipine type yielded very low affinity to other receptors measured in brain and heart membranes. 3H-BAY K 8644 binding sites proved to be highly specific for various potently displacing DHP derivatives and discriminated between optical isomers (stereoselectivity) with inhibition constants (Ki) in the nanomolar range. The heterogeneous shapes of the competition curves also imply interactions of these compounds with different (sub-)sites of the DHP receptor that represents one locus of interaction in regulating transmembranal Ca2+ currents. The other specific site of action for the potent diphenylalkylamines, clearly different to the DHP receptor was characterized with 3H-verapamil. The equilibrium dissociation constant, Kd in cultured myocytes ranged between 16-25 nM, and binding capacity, Bmax amounted to about 1.85 pmol/mg of protein. The different mode of competitions indicates the involvement of more than one 3H-verapamil binding site. The interrelation of the structurally heterogeneous channel modulators with the differently radiolabelled receptor (sub-)sites located in or near by the calcium channel may represent new approaches in investigating the nature of action of these potent compounds.
在搏动心肌细胞的单层培养物中证实了钙通道激活二氢吡啶（DHP）H-BAY K 8644以及抑制性3H-维拉帕米的结合特性。3H-BAY K 8644特异性结合依赖于细胞外钙的存在，亲和力受Ca2+调节，但希尔系数不受影响。BAY K 8644刺激静息和搏动心肌细胞的心肌收缩力。然而，与β-肾上腺素能受体激动剂不同，该化合物对培养心肌细胞中环磷酸腺苷（cAMP）和环磷酸鸟苷（cGMP）的细胞水平没有影响。钙通道激活剂BAY K 8644以及硝苯地平或尼莫地平类型的Ca2+内流阻断二氢吡啶的二氢吡啶衍生物对在脑和心脏膜中测量的其他受体的亲和力非常低。3H-BAY K 8644结合位点被证明对各种强效取代二氢吡啶衍生物具有高度特异性，并能区分光学异构体（立体选择性），抑制常数（Ki）在纳摩尔范围内。竞争曲线的异质形状也意味着这些化合物与二氢吡啶受体的不同（亚）位点相互作用，该受体代表调节跨膜Ca2+电流的一个相互作用位点。强效二苯烷基胺的另一个特异性作用位点与二氢吡啶受体明显不同，用3H-维拉帕米进行了表征。培养心肌细胞中的平衡解离常数Kd在16 - 25 nM之间，结合容量Bmax约为1.85 pmol/mg蛋白质。不同的竞争模式表明存在不止一个3H-维拉帕米结合位点。结构异质的通道调节剂与位于钙通道内或附近的不同放射性标记受体（亚）位点之间的相互关系可能代表了研究这些强效化合物作用性质的新方法。
