Jóna I, Szegedi C, Sárközi S, Szentesi P, Csernoch L, Kovács L
Department of Physiology, University of Debrecen, Medical School, Hungary.
Pflugers Arch. 2001 Mar;441(6):729-38. doi: 10.1007/s004240000484.
Magnesium-induced inhibition of the skeletal ryanodine receptor/calcium-release channel (RyR) was studied in the presence and absence of ATP under isolated conditions and in situ, by examining the RyR incorporated into a planar lipid bilayer and the calcium release flux (Rrel) in isolated single fibres mounted in the double Vaseline gap system. When the incorporated RyR had been activated by calcium (50 microM) in the absence of ATP, the magnesium-induced inhibition showed co-operativity with a Hill coefficient (N) of 1.83 and a half-inhibitory concentration (IC50) of 635 microM. When the open probability was measured in the presence of 5 mM ATP and at a low calcium concentration, the magnesium-induced inhibition was non-cooperative (N=1.1, IC50= 860 microM). In isolated muscle fibres, in the presence of ATP, lowering the intracellular magnesium concentration ([Mg2+]i) increased the maximal Rrel and shifted its voltage dependence to more negative membrane potentials. Increasing [Mg2+]i had the opposite effect. The concentration dependence was described with an IC50 of 174 microM, N=1, under depolarized conditions and showed a tenfold increase in affinity in polarized fibres. At the concentration required for the measurements from isolated fibres, ATP had a full activatory effect on the isolated channel. At a low calcium concentration, the RyR had two ATP-binding sites with half-activatory concentrations of 19 and 350 microM, respectively.
在有ATP和无ATP的情况下，通过检测整合到平面脂质双层中的兰尼碱受体/钙释放通道（RyR）以及安装在双凡士林间隙系统中的分离单纤维中的钙释放通量（Rrel），在离体条件下和原位研究了镁对骨骼肌兰尼碱受体/钙释放通道（RyR）的抑制作用。当在无ATP的情况下，整合的RyR被钙（50μM）激活时，镁诱导的抑制表现出协同性，希尔系数（N）为1.83，半抑制浓度（IC50）为635μM。当在5 mM ATP存在下且钙浓度较低时测量开放概率，镁诱导的抑制是非协同的（N = 1.1，IC50 = 860μM）。在分离的肌纤维中，在有ATP的情况下，降低细胞内镁浓度（[Mg2+]i）可增加最大Rrel，并将其电压依赖性转移到更负的膜电位。增加[Mg2+]i则产生相反的效果。浓度依赖性在去极化条件下用IC50为174μM、N = 1来描述，并且在极化纤维中亲和力增加了10倍。在从分离纤维进行测量所需的浓度下，ATP对分离的通道具有完全激活作用。在低钙浓度下，RyR有两个ATP结合位点，半激活浓度分别为19和350μM。
