Haworth R A, Redon D, Biggs A V, Potter K T
Department of Anesthesiology, University of Wisconsin, Madison, USA.
Cell Calcium. 1998 Apr;23(4):199-205. doi: 10.1016/s0143-4160(98)90118-x.
The rate of verapamil-sensitive uptake of 45Ca by rat heart cells stimulated to beat in suspension with 0.2 mM Ca and isoproterenol was increased > 2-fold by cell loading with the chelator Quin-2. No effect of Quin-2 loading was observed on the rate of uptake of trace levels of 54Mn, present in addition to Ca, which was used as an index of Ca channel activity. Quin-2 loading also had little effect on the rate of 45Ca uptake by cells diluted into a high K/low Na medium, where Ca uptake was primarily by Na/Ca exchange. The fast chelator 1,2-bis(o-aminophenoxy)ethane-N,N,-N',N'-tetraacetic acid (BAPTA) was 3-fold more effective than the slow chelator EGTA at preventing Ca efflux. BAPTA loading also caused an increase in sarcoplasmic reticulum (SR) Ca content. These results suggest that chelator loading had little effect on the rate of Ca influx by Ca channels or by Na/Ca exchange, and that the increased rate of 45Ca uptake seen with Quin-2 loading was caused by an inhibition of Ca efflux, either directly by chelation or by increased Ca uptake by the SR or by other intracellular organelles. This further suggests that most of the Ca entering the cell without chelator leaves again within the same beat, and that this may result from Ca efflux from a kinetically limited Ca pool in or around the diad cleft.
用0.2 mM钙和异丙肾上腺素刺激悬浮状态下搏动的大鼠心脏细胞，45Ca对维拉帕米敏感的摄取速率在细胞用螯合剂喹啉-2加载后增加了2倍以上。除钙外还存在的微量54Mn的摄取速率未观察到喹啉-2加载的影响，54Mn用作钙通道活性的指标。喹啉-2加载对稀释至高钾/低钠培养基中的细胞摄取45Ca的速率也几乎没有影响，在该培养基中钙摄取主要通过钠/钙交换进行。快速螯合剂1,2-双（邻氨基苯氧基）乙烷-N，N，-N'，N'-四乙酸（BAPTA）在防止钙外流方面比慢速螯合剂乙二醇双四乙酸（EGTA）有效3倍。BAPTA加载还导致肌浆网（SR）钙含量增加。这些结果表明，螯合剂加载对通过钙通道或钠/钙交换的钙内流速率几乎没有影响，并且喹啉-2加载时观察到的45Ca摄取速率增加是由钙外流的抑制引起的，要么直接通过螯合，要么通过SR或其他细胞内细胞器增加钙摄取。这进一步表明，在没有螯合剂的情况下进入细胞的大部分钙在同一搏动内再次离开，这可能是由于从二联体裂隙内或周围动力学受限的钙池中钙外流所致。
