Bae Min, Kim Suk, Ko Euna, Lee Suk-Ho, Ho Won-Kyung, Earm Yung E
Department of Physiology, Konkuk University College of Medicine, 322 Danwol-dong, Choongju 380-701, Korea.
Pflugers Arch. 2002 Jul;444(4):523-31. doi: 10.1007/s00424-002-0850-9. Epub 2002 Apr 25.
We investigated the role of intracellular Mg(2+) (Mg(2+)) in the regulation of membrane potential ( V(m)) in rabbit coronary artery smooth muscle cells. V(m), membrane currents and intracellular Ca(2+) (Ca(2+)) were measured using standard patch-clamp and microfluorometry techniques. When Ca(2+) was increased by caffeine, V(m) depolarized at low Mg(2+) (0.1 mM), but hyperpolarized at high Mg(2+) (> or =1.2 mM). Effects of Mg(2+) on caffeine-induced currents were investigated. Mg(2+) selectively facilitated the activation of Ca(2+)-activated K(+) currents ( I(K,Ca)), while Ca(2+)-activated Cl(-) currents ( I(Cl,Ca)) were unaffected. Simultaneous recording of Ca(2+) and I(K,Ca) at different Mg(2+) showed that Mg(2+) increased the Ca(2+) sensitivity of I(K,Ca). Ca(2+) also inhibited voltage-dependent K(+) (K(V)) currents, although this effect was significant only at low Mg(2+). These results imply that the relative contributions of I(K,Ca), I(Cl,Ca) and K(V) currents to V(m) during an increase in Ca(2+) are affected by Mg(2+): at low Mg(2+), activation of I(Cl,Ca) and inhibition of K(V) currents depolarized V(m); at high Mg(2+) the activation of I(K,Ca) predominated, resulting in hyperpolarization of V(m). In conclusion, Mg(2+) hyperpolarizes V(m) by selective facilitation of I(K,Ca) and may thus possibly contributes to the relaxation of the coronary artery.
我们研究了细胞内镁离子（Mg(2+)）在兔冠状动脉平滑肌细胞膜电位（V(m)）调节中的作用。使用标准膜片钳和显微荧光测定技术测量V(m)、膜电流和细胞内钙离子（Ca(2+)）。当用咖啡因使Ca(2+)升高时，在低Mg(2+)（0.1 mM）时V(m)去极化，但在高Mg(2+)（≥1.2 mM）时V(m)超极化。研究了Mg(2+)对咖啡因诱导电流的影响。Mg(2+)选择性地促进钙激活钾电流（I(K,Ca)）的激活，而钙激活氯电流（I(Cl,Ca)）不受影响。在不同Mg(2+)下同时记录Ca(2+)和I(K,Ca)表明，Mg(2+)增加了I(K,Ca)对钙的敏感性。Ca(2+)也抑制电压依赖性钾（K(V)）电流，尽管这种作用仅在低Mg(2+)时显著。这些结果表明，在Ca(2+)升高期间，I(K,Ca)、I(Cl,Ca)和K(V)电流对V(m)的相对贡献受Mg(2+)影响：在低Mg(2+)时，I(Cl,Ca)的激活和K(V)电流的抑制使V(m)去极化；在高Mg(2+)时，I(K,Ca)的激活占主导，导致V(m)超极化。总之，Mg(2+)通过选择性促进I(K,Ca)使V(m)超极化，因此可能有助于冠状动脉的舒张。
