Carafoli E
Laboratory of Biochemistry, Swiss Federal Institute of Technology (ETH), Zurich.
J Cardiovasc Pharmacol. 1988;12 Suppl 3:S77-84.
Calcium is a signaling element of general importance to cells. In muscle, its key function is the activation of troponin C, which is essential for the contraction of myofibrils in skeletal and heart muscles, and of myosin light chain kinase, which is essential for the contraction of smooth muscles. Calcium modulates the latter enzyme through the calcium-binding protein calmodulin, which may also control other calcium-binding proteins involved in the contraction of smooth muscles. The control of calcium within cells requires the reversible and specific complexation by proteins that are either soluble in the cytoplasm (e.g., calmodulin), intrinsic to membranes (e.g., ATPases, Ca exchangers), or organized in nonmembranous structures (e.g., troponin C). Two Ca pumps (i.e., ATPases) are responsible for a large portion of the Ca movements across membrane barriers. One is located in sarco(endo)plasmic reticulum; in muscles, it moves back and forth the Ca2+ that is directly involved in the activation of the myofibrils. The other is located in the plasma membrane. Together with a Na/Ca exchanger that is also located there, it maintains the large Ca gradient normally existing between cells and extracellular spaces.
钙是一种对细胞具有普遍重要性的信号传导元素。在肌肉中，其关键功能是激活肌钙蛋白C，这对骨骼肌和心肌中肌原纤维的收缩至关重要，以及激活肌球蛋白轻链激酶，这对平滑肌的收缩至关重要。钙通过钙结合蛋白钙调蛋白调节后一种酶，钙调蛋白也可能控制参与平滑肌收缩的其他钙结合蛋白。细胞内钙的控制需要由可溶于细胞质的蛋白质（如钙调蛋白）、膜内在蛋白（如ATP酶、钙交换器）或组织在非膜结构中的蛋白质（如肌钙蛋白C）进行可逆且特异性的络合。两种钙泵（即ATP酶）负责大部分跨膜屏障的钙转运。一种位于肌浆（内质）网；在肌肉中，它来回移动直接参与肌原纤维激活的Ca2+。另一种位于质膜。它与同样位于那里的钠/钙交换器一起，维持细胞与细胞外空间之间通常存在的大钙梯度。
