Hurley T W, Ryan M P
Department of Child Health, University of Missouri Health Sciences Center, Columbia 65212.
Arch Oral Biol. 1988;33(11):793-800. doi: 10.1016/0003-9969(88)90103-3.
Active Ca2+ transport was studied in acini that had been permeabilized by incubation in buffer nominally free of Ca2+ in order to avoid any contribution to measured Ca2+ uptake by elements of the plasma membrane. In most experiments, ruthenium red was used to inhibit mitochondrial Ca2+ uptake. Non-mitochondrial Ca2+ transport was greatest at pH 7.0-7.5 and required Mg2+-ATP at concentrations typical of the cytosol (K0.5 = 1.36 +/- 0.53 mM). Other substrates were much less effective than ATP. Ca2+ uptake was stimulated by Ca2+ at concentrations near those measured in intact cells (K0.5 = 0.43 +/- 0.17 microM). Hill coefficients at subsaturating concentrations of Ca2+ (1.08 +/- 0.27) and Mg2+-ATP (0.81 +/- 0.22) indicated that cooperative interactions are not characteristic of the major cationic regulators of Ca2+ transporting activity. Na+ did not release Ca2+ from acinar mitochondria, but consistently reduced non-mitochondrial Ca2+ uptake by about 20% as compared to uptake in the presence of an equimolar K+ concentration. The properties of non-mitochondrial Ca2+ uptake in permeabilized acini are similar to those of high affinity Ca2+ uptake which, in broken cell preparations, has been found distributed in parallel with elements of the endoplasmic reticulum. The Ca2+-sequestering properties of a non-mitochondrial organelle in permeabilized submandibular gland acini are those expected of a principal regulator of cytosolic Ca2+ and could account for the ionized Ca2+ concentration measured in resting salivary acinar cells.
为避免质膜成分对测量的钙离子摄取产生任何影响，在名义上不含钙离子的缓冲液中孵育使腺泡通透后，研究了活性钙离子转运。在大多数实验中，使用钌红抑制线粒体对钙离子的摄取。非线粒体钙离子转运在pH 7.0 - 7.5时最大，并且需要胞质溶胶典型浓度的镁 - 三磷酸腺苷（K0.5 = 1.36 ± 0.53 mM）。其他底物的效果远不如三磷酸腺苷。接近完整细胞中测量浓度的钙离子（K0.5 = 0.43 ± 0.17 microM）刺激钙离子摄取。在钙离子（1.08 ± 0.27）和镁 - 三磷酸腺苷（0.81 ± 0.22）亚饱和浓度下的希尔系数表明，协同相互作用不是钙离子转运活性的主要阳离子调节因子的特征。钠离子不会从腺泡线粒体中释放钙离子，但与等摩尔钾离子浓度存在时的摄取相比，始终使非线粒体钙离子摄取减少约20％。通透腺泡中非线粒体钙离子摄取的特性类似于高亲和力钙离子摄取的特性，在破碎细胞制剂中，已发现其与内质网成分平行分布。通透的下颌下腺腺泡中非线粒体细胞器的钙离子螯合特性是胞质钙离子主要调节因子所预期的，并且可以解释在静息唾液腺泡细胞中测量的游离钙离子浓度。
