Eggermont J A, Vrolix M, Raeymaekers L, Wuytack F, Casteels R
Laboratorium voor Fysiologie, Universiteit Leuven, Belgium.
Circ Res. 1988 Feb;62(2):266-78. doi: 10.1161/01.res.62.2.266.
To characterize the Ca2+-transport properties of the plasma membrane and of the endoplasmic reticulum of bovine pulmonary artery, membrane vesicles are subfractionated by a procedure of density-gradient centrifugation that takes advantage of the selective effect of digitonin on the density of plasma-membrane vesicles. The obtained endoplasmic-reticulum fraction contains hardly any plasma-membrane vesicles, whereas the plasma-membrane fraction is still contaminated by a substantial amount of endoplasmic-reticulum vesicles. An adenosine 5'-triphosphate (ATP) energized Ca2+-transport system and a Ca2+-stimulated ATPase activity are present in both subcellular fractions. The Ca2+ transport by the plasma membrane is catalyzed by a (Ca2+,Mg2+)-ATPase of Mr 130,000. It binds calmodulin and it has a low steady-state phosphoprotein intermediate level. The endoplasmic-reticulum vesicles contain a Ca2+-transport ATPase of Mr 100,000 that is characterized by a high steady-state phosphointermediate level. It is antigenically related to the Ca2+-pump protein of cardiac sarcoplasmic reticulum. Phospholamban, the regulatory protein of the Ca2+-transport enzyme of cardiac sarcoplasmic reticulum, is also present in the endoplasmic reticulum of the pulmonary artery. A comparison of these fractions with the previously characterized fractions from porcine gastric smooth muscle reveals important differences in the basal Mg2-ATPase activity, in the ratio of the (Ca2+,Mg2+)-ATPase of the plasmalemma to that of the endoplasmic reticulum, and in the ratio of the (Na+,K+)-ATPase activity to the plasmalemmal (Ca2+,Mg2+)-ATPase activity. These differences can be ascribed in part to the species and in part to the tissue. These data suggest that in the bovine pulmonary artery the Ca2+ extrusion via the ATP-dependent Ca2+ pump may have a less predominant role, and that the Ca2+ uptake by the endoplasmic reticulum, and possibly also the Ca2+ extrusion via the Na+-Ca2+ exchanger could be more important in this tissue than in the porcine stomach.
为了表征牛肺动脉质膜和内质网的钙离子转运特性，利用洋地黄皂苷对质膜囊泡密度的选择性作用，通过密度梯度离心法对膜囊泡进行亚分级分离。获得的内质网部分几乎不含有任何质膜囊泡，而质膜部分仍被大量内质网囊泡污染。两个亚细胞部分均存在腺苷5'-三磷酸（ATP）驱动的钙离子转运系统和钙离子刺激的ATP酶活性。质膜的钙离子转运由分子量为130,000的（Ca2 +，Mg2 +）-ATP酶催化。它结合钙调蛋白，并且具有低稳态磷蛋白中间水平。内质网囊泡含有分子量为100,000的钙离子转运ATP酶，其特征在于高稳态磷中间水平。它与心脏肌浆网的钙离子泵蛋白具有抗原相关性。心脏肌浆网钙离子转运酶的调节蛋白受磷蛋白调节，也存在于肺动脉的内质网中。将这些部分与先前表征的猪胃平滑肌部分进行比较，发现在基础Mg2-ATP酶活性、质膜（Ca2 +，Mg2 +）-ATP酶与内质网的比率以及（Na +，K +）-ATP酶活性与质膜（Ca2 +，Mg2 +）-ATP酶活性的比率方面存在重要差异。这些差异部分可归因于物种，部分可归因于组织。这些数据表明，在牛肺动脉中，通过ATP依赖性钙离子泵的钙离子外排可能起的作用较小，并且内质网对钙离子的摄取以及可能通过钠钙交换器的钙离子外排在该组织中可能比在猪胃中更重要。
