Tupper J T, Del Rosso M, Hazelton B, Zorgniotti F
J Cell Physiol. 1978 Apr;95(1):71-84. doi: 10.1002/jcp.1040950110.
Serum stimulation of quiescent 3T3 cells returns the cells to a proliferative state. Changes in Ca content, transport and distribution during the transition through G1 and S phase have been investigated following serum stimulation of these cells. 45 Ca exchange data indicate at least two kinetically defined cellular compartments for Ca; a rapidly exchanging component presumably representing surface Ca which is removable by EGTA and a slowly exchanging component presumably representing cytoplasmically located Ca. Previous studies (Tupper and Zorgniotti, '77) indicate that the approach to quiescence in the 3T3 cells is characterized by a large increase in the surface Ca component. The present data demonstrate that this component is rapidly lost following serum stimulation. Furthermore, the serum induces an 8-fold increase in Ca influx into the cytoplasmic compartment and a reduction in the unidirectional efflux rate coefficient for Ca. The increased Ca uptake peaks at approximately six hours (mid G1) and is accompanied by a parallel increase in cellular Ca. Prior to entrance of the cells into S phase (10-12 hours), Ca uptake declines. This is followed by a slower decline in cytoplasmic Ca levels. Simultaneous addition to fresh serum plus 0.5 mM dibutryl cAMP inhibits the entrance of the cells into S phase. Under these conditions the loss of surface Ca is not blocked. However, the presence of 0.5 mM dibutyryl cAMP inhibits the increase in Ca uptake and, in turn, diminishes the increase in cellular Ca following serum stimulation. In contrast, a low level of dibutyryl cAMP (0.1 mM) enhances progression through G1 phase but also reduces both Ca uptake and Ca content of the cells. The data suggest that the serum induced changes in Ca content and transport are linked to intracellular cyclic nucleotide levels and progression through G1 phase and that extracellular cAMP elevating agents may enhance of inhibit these interactions in a concentration dependent manner.
血清刺激静止的3T3细胞可使细胞恢复增殖状态。在血清刺激这些细胞后，研究了细胞在通过G1期和S期转变过程中钙含量、转运和分布的变化。45Ca交换数据表明，钙至少存在两个动力学定义的细胞区室；一个快速交换组分可能代表可被EGTA去除的表面钙，一个缓慢交换组分可能代表位于细胞质中的钙。先前的研究（Tupper和Zorgniotti，1977年）表明，3T3细胞静止过程的特点是表面钙组分大幅增加。目前的数据表明，血清刺激后该组分迅速丢失。此外，血清诱导钙流入细胞质区室增加8倍，并降低钙的单向流出速率系数。钙摄取增加在大约6小时（G1中期）达到峰值，并伴随着细胞内钙的平行增加。在细胞进入S期（10 - 12小时）之前，钙摄取下降。随后细胞质钙水平缓慢下降。同时添加新鲜血清加0.5 mM二丁酰cAMP可抑制细胞进入S期。在这些条件下，表面钙的丢失未被阻断。然而，0.5 mM二丁酰cAMP的存在抑制了钙摄取的增加，进而减少了血清刺激后细胞内钙的增加。相反，低水平的二丁酰cAMP（0.1 mM）促进细胞通过G1期，但也降低了细胞的钙摄取和钙含量。数据表明，血清诱导的钙含量和转运变化与细胞内环核苷酸水平以及通过G1期的进程有关，并且细胞外cAMP升高剂可能以浓度依赖的方式增强或抑制这些相互作用。
