Stout M A
Department of PHysiology, UMDNJ-New Jersey Medical School, Newark 07103-2714.
J Cell Physiol. 1991 Dec;149(3):383-95. doi: 10.1002/jcp.1041490305.
The components of 45calcium (Ca) uptake were studied in saponin skinned rat caudal artery. The steady-state Ca content increased when the free Ca concentration was varied from 10(-8) to 10(-4) M but was reduced by azide when the free Ca concentration exceeded 3.1 microM. The azide sensitivity and low affinity for Ca were consistent with functional mitochondria. The azide-insensitive component consisted of a small bound and a larger releasable Ca fraction. After skinning in Triton X-100, approximately 4 mumol Ca/kg wet tissue remained, which represented a tightly bound but slowly exchangeable Ca pool. The Ca content was independent of the free Ca concentration and MgATP, and it was not released with A-23187 or Ca. The Ca content of the larger fraction was a higher order function of the free Ca concentration and was released with A-23187, indicating it resided within a membrane-bounded structure. Ca uptake by the releasable fraction was increased by oxalate, MgATP, phosphocreatine, temperature, phosphate, and ruthenium red and represents Ca sequestered by the sarcoplasmic reticulum (SR) with little contribution from other Ca binding or storage sites. It is described by the coefficients Umax = 96.94 mumol/kg wet tissue, K1/2 = 0.75 microM, and Hill coefficient = 1.70. The SR in this preparation regulates cytosolic Ca concentrations under physiological conditions and can accumulate Ca by MgATP-dependent and MgATP-independent process. The larger, MgATP-dependent Ca uptake is described by the coefficients Umax = 72.87 mumol/kg wet tissue, K1/2 = 0.8 microM, and Hill coefficient = 2.09 and is consistent with Ca sequestered by the Ca-transport ATPase of smooth muscle SR. The smaller, MgATP-independent uptake is described by the coefficients Umax = 24.14 mumol/kg wet tissue, K1/2 = 0.56 microM, and Hill coefficient = 1.01 and represents Ca sequestered by an unidentified mechanism or by a subpopulation of SR.
在皂角苷透皮处理的大鼠尾动脉中研究了45钙（Ca）摄取的成分。当游离钙浓度从10⁻⁸变化到10⁻⁴M时，稳态钙含量增加，但当游离钙浓度超过3.1微摩尔时，叠氮化物会使其降低。叠氮化物敏感性和对钙的低亲和力与功能性线粒体一致。叠氮化物不敏感成分由一小部分结合钙和一大部分可释放钙组成。在Triton X - 100中透皮处理后，每千克湿组织约有4微摩尔钙残留，这代表一个紧密结合但缓慢可交换的钙库。钙含量与游离钙浓度和MgATP无关，且不会被A - 23187或钙释放。较大部分的钙含量是游离钙浓度的高阶函数，并会被A - 23187释放，表明其存在于膜结合结构内。草酸盐、MgATP、磷酸肌酸、温度、磷酸盐和钌红会增加可释放部分的钙摄取，这代表钙被肌浆网（SR）隔离，其他钙结合或储存位点贡献很小。其系数描述为Umax = 96.94微摩尔/千克湿组织，K1/2 = 0.75微摩尔，希尔系数 = 1.70。该制剂中的SR在生理条件下调节胞质钙浓度，并可通过依赖MgATP和不依赖MgATP的过程积累钙。较大的、依赖MgATP的钙摄取系数描述为Umax = 72.87微摩尔/千克湿组织，K1/2 = 0.8微摩尔，希尔系数 = 2.09，与平滑肌SR的钙转运ATP酶隔离的钙一致。较小的、不依赖MgATP的摄取系数描述为Umax = 24.14微摩尔/千克湿组织，K1/2 = 0.56微摩尔，希尔系数 = 1.01，代表通过未知机制或SR亚群隔离的钙。
