Galizzi J P, Fosset M, Lazdunski M
Eur J Biochem. 1984 Oct 15;144(2):211-5. doi: 10.1111/j.1432-1033.1984.tb08451.x.
The verapamil receptor associated with the voltage-dependent calcium channel of rabbit skeletal muscle transverse tubule membranes has the following properties. (i) This receptor is stereospecific and discriminates between the different stereoisomers of verapamil, gallopamil and diltiazem. (ii) Inorganic divalent cations inhibit the binding of [3H]verapamil to its receptor in an apparently non-competitive fashion. The rank order of potency is: Ca2+ = Mn2+ greater than Mg2+ greater than Sr2+ greater than Ba2+ much greater than Co2+ much greater than Ni2+. Ca2+ and Mn2+ have inhibition constants of 0.3 mM. Binding of [3H]verapamil is also sensitive to monovalent cations such as Cs+, K+, Li+ and Na+. The most active of these cations (Cs+ and K+) have inhibition constants in the range of 30 mM. (iii) Binding of [3H]verapamil is pH-dependent and reveals the presence on the verapamil receptor of an essential ionizable group with a pKa of 6.5. (iv) A low-affinity binding site for verapamil and for some other Ca2+ channel blockers is detected by studies of dissociation kinetics of the [3H]verapamil receptor in the presence of high concentrations of verapamil, gallopamil, bepridil and diltiazem. (v) GTP and nucleoside analogs change the properties of [3H]verapamil binding to verapamil binding sites. High-affinity binding sites seem to be transferred into low-affinity sites. Dissociation constants obtained from inhibition studies of [3H]verapamil binding are in the range of 0.1-0.3 mM for GTP, ATP and Gpp(NH)p.
与兔骨骼肌横管膜电压依赖性钙通道相关的维拉帕米受体具有以下特性。(i) 该受体具有立体特异性，可区分维拉帕米、加洛帕米和地尔硫䓬的不同立体异构体。(ii) 无机二价阳离子以明显的非竞争性方式抑制 [³H]维拉帕米与其受体的结合。效力的排序为：Ca²⁺ = Mn²⁺ ＞ Mg²⁺ ＞ Sr²⁺ ＞ Ba²⁺ ＞＞ Co²⁺ ＞＞ Ni²⁺。Ca²⁺ 和 Mn²⁺ 的抑制常数为 0.3 mM。[³H]维拉帕米的结合也对一价阳离子如 Cs⁺、K⁺、Li⁺ 和 Na⁺ 敏感。这些阳离子中最具活性的（Cs⁺ 和 K⁺）抑制常数在 30 mM 范围内。(iii) [³H]维拉帕米的结合依赖于 pH，并揭示了维拉帕米受体上存在一个必需的可电离基团，其 pKa 为 6.5。(iv) 通过在高浓度维拉帕米、加洛帕米、苄普地尔和地尔硫䓬存在下研究 [³H]维拉帕米受体的解离动力学，检测到了维拉帕米和其他一些钙通道阻滞剂的低亲和力结合位点。(v) GTP 和核苷类似物改变 [³H]维拉帕米与维拉帕米结合位点结合的特性。高亲和力结合位点似乎转变为低亲和力位点。从 [³H]维拉帕米结合抑制研究中获得的 GTP、ATP 和 Gpp(NH)p 的解离常数在 0.1 - 0.3 mM 范围内。
