Haworth R A, Goknur A B, Hunter D R
Department of Anesthesiology, University of Wisconsin Clinical Science Center, Madison 53792.
Circ Res. 1991 Dec;69(6):1506-13. doi: 10.1161/01.res.69.6.1506.
Isolated adult rat heart cells in suspension were loaded with sodium by incubation with ouabain in the absence of calcium for 30 minutes. Addition of low levels of calcium induced accelerated rates of sodium influx and efflux, as measured with 22Na. The magnitude of calcium-induced 22Na efflux was 50-fold greater than the net rate of calcium uptake and required extracellular sodium, but not extracellular calcium, once some calcium was taken up. Calcium did not induce 86Rb efflux. The accelerated rate of 22Na efflux was prevented by verapamil, but verapamil was ineffective when added after calcium. Addition of EGTA after calcium reversed the effect of calcium, but only after incubation. Dichlorobenzamil, unlike verapamil, both prevented and reversed the induction of sodium fluxes by calcium. We conclude 1) that intracellular calcium induces Na-Na exchange through the Na-Ca exchanger in sodium-loaded cells exposed to calcium; and 2) that Na-Na exchange can be activated by calcium that enters the cell through calcium channels. We propose that this Na-Na exchange reflects the intrinsic activity of the Na-Ca exchanger.
将成年大鼠的离体悬浮心脏细胞在无钙条件下与哇巴因孵育30分钟，使其负载钠。加入低水平的钙会诱导钠流入和流出速率加快，这是用22Na测量的。钙诱导的22Na流出量比钙摄取的净速率大50倍，并且一旦摄取了一些钙，就需要细胞外钠而不是细胞外钙。钙不会诱导86Rb流出。维拉帕米可阻止22Na流出速率的加快，但在加入钙后再添加维拉帕米则无效。在加入钙后添加EGTA可逆转钙的作用，但仅在孵育后有效。与维拉帕米不同，二氯苯甲酰胺既能阻止又能逆转钙对钠通量的诱导。我们得出结论：1）细胞内钙通过钠-钙交换体在暴露于钙的钠负载细胞中诱导钠-钠交换；2）钠-钠交换可被通过钙通道进入细胞的钙激活。我们提出这种钠-钠交换反映了钠-钙交换体的内在活性。
