Colca J R, Kotagal N, Lacy P E, McDaniel M L
Biochem J. 1983 Apr 15;212(1):113-21. doi: 10.1042/bj2120113.
The possible effects of calmodulin and cyclic AMP on active Ca2+ uptake by the islet-cell endoplasmic reticulum were investigated. Neither calmodulin nor cyclic AMP affected the rate of active Ca2+ uptake, or the steady-state filling capacity of the endoplasmic reticulum when measured in the absence of oxalate. Consistent with these results, calmodulin did not activate the Ca2+-stimulated ATPase activity associated with this cell fraction. During the course of these experiments., it was unexpectedly discovered that the rate of Ca2+ uptake, as well as the steady-state Ca2+ filling capacity of the endoplasmic reticulum, were markedly increased by unidentified factor(s) in the cytosol. This effect could be demonstrated by reconstitution of the membranes in cytosol, or by direct addition of fresh or dialysed cytosol to the Ca2+ uptake assays. The degree of activation by the cytosol indicates that the endoplasmic reticulum may play a prominent role in controlling beta-cell Ca2+ concentrations and that the unidentified activator(s) present in the cytosol may be involved in regulation of this function.
研究了钙调蛋白和环磷酸腺苷（cAMP）对胰岛细胞内质网主动摄取Ca2+的可能影响。在不存在草酸盐的情况下进行测量时，钙调蛋白和环磷酸腺苷均未影响主动摄取Ca2+的速率或内质网的稳态填充能力。与这些结果一致，钙调蛋白未激活与此细胞组分相关的Ca2+刺激的ATP酶活性。在这些实验过程中，意外发现细胞质中的未知因子显著提高了Ca2+摄取速率以及内质网的稳态Ca2+填充能力。通过在细胞质中重建膜，或通过将新鲜的或透析过的细胞质直接添加到Ca2+摄取试验中，可以证明这种效应。细胞质的激活程度表明内质网可能在控制β细胞Ca2+浓度方面发挥重要作用，并且细胞质中存在的未知激活剂可能参与此功能的调节。
