在鱿鱼轴突中，三磷酸腺苷（ATP）通过一种依赖于细胞内钙离子（Ca2+ i）的磷酸化作用来调节钠钙交换。

In squid axons, ATP modulates Na+-Ca2+ exchange by a Ca2+i-dependent phosphorylation.

作者信息

DiPolo R, Beaugé L

出版信息

Biochim Biophys Acta. 1987 Mar 12;897(3):347-54. doi: 10.1016/0005-2736(87)90432-9.

Abstract

In squid axons ATP stimulates both the forward and reverse modes of the Na+-Ca2+ exchange by changing the affinity of the carrier towards Na+ and Ca2+ ions. Whether ATP activates the Na+-Ca2+ antiporter allosterically or is hydrolyzed during activation is still debated. The hypothesis that ATP modulates the Na+-Ca2+ exchange through phosphorylation has been tested by means of [gamma-S]ATP, an ATP analog that can act as a substrate for kinases but not for ATPases. Steady-state Ca2+ efflux was measured in squid axons dialyzed without ATP and containing either 0.7 or 100 microM Ca2+i. Addition of 1 mM [gamma-S]ATP markedly increases the Na+o-dependent component of the Ca2+ efflux. The activation by [gamma-S]ATP: requires the presence of Mg2+i, is partially reversible upon removing the analog, is greater than that caused by ATP and only operates on the exchange system since no activation of the ATP-dependent uncoupled Ca2+ efflux (Ca2+ pump) can be detected. 22Na+ experiments were used to monitor the Cao-dependent Na+ efflux (reverse Na+-Ca2+ exchange). Without Ca2+i and ATP, Na+ efflux is very small ('leak'). [gamma-S]ATP does not activate the efflux of Na+ in the absence of Ca2+i. In the presence of Ca2+i the ATP analog stimulates both the Cao- and Nao-dependent Na+ efflux components. Interestingly, neither the Na+ pump, Ca2+i-independent Na+-Na+ exchange, Nai+-Mg2+i exchange or Na+/K+/Cl- cotransport are affected by [gamma-S]ATP. The experiments indicate that a Ca2+i-dependent phosphorylation occurs during the activation of the Na+-Ca2+ exchange by ATP.

摘要

在鱿鱼轴突中，ATP通过改变载体对Na⁺和Ca²⁺离子的亲和力来刺激Na⁺-Ca²⁺交换的正向和反向模式。ATP是通过变构激活Na⁺-Ca²⁺反向转运体还是在激活过程中被水解，目前仍存在争议。ATP通过磷酸化调节Na⁺-Ca²⁺交换的假说已通过[γ-S]ATP进行了验证，[γ-S]ATP是一种ATP类似物，可作为激酶的底物，但不能作为ATP酶的底物。在没有ATP且含有0.7或100μM细胞内Ca²⁺（Ca²⁺i）的情况下，对鱿鱼轴突进行透析，测量稳态Ca²⁺外流。添加1 mM [γ-S]ATP可显著增加Ca²⁺外流中依赖细胞外Na⁺（Na⁺o）的成分。[γ-S]ATP的激活：需要细胞内Mg²⁺（Mg²⁺i）的存在，去除该类似物后部分可逆，大于ATP引起的激活，并且仅作用于交换系统，因为未检测到对依赖ATP的非耦合Ca²⁺外流（Ca²⁺泵）的激活。利用²²Na⁺实验监测依赖细胞外Ca²⁺（Ca⁺o）的Na⁺外流（反向Na⁺-Ca²⁺交换）。在没有Ca²⁺i和ATP的情况下，Na⁺外流非常小（“渗漏”）。在没有Ca²⁺i的情况下，[γ-S]ATP不会激活Na⁺外流。在存在Ca²⁺i的情况下，该ATP类似物会刺激依赖Ca⁺o和Na⁺o的Na⁺外流成分。有趣的是，[γ-S]ATP对Na⁺泵、不依赖Ca²⁺i的Na⁺-Na⁺交换、细胞内Na⁺（Nai⁺）-Mg²⁺i交换或Na⁺/K⁺/Cl⁻协同转运均无影响。这些实验表明，在ATP激活Na⁺-Ca²⁺交换的过程中会发生依赖Ca²⁺i的磷酸化。