ATP dependence of Na+-driven Cl-HCO3 exchange in squid axons.
ATP dependence of Na+-driven Cl-HCO3 exchange in squid axons.
复制标题
鱿鱼轴突中 Na 驱动的 Cl-HCO3 交换的 ATP 依赖性。
DOI：
10.1007/s00232-008-9100-1
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
Boron,WalterF
中科院分区：
文献类型：
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作者：
Davis,BruceA;Hogan,EmiliaM;Russell,JohnM;Boron,WalterF
鱿鱼巨型轴突通过激活Na+驱动的氯-HCO3交换器从酸负荷中恢复。我们将轴突内部透析至细胞内pH(Phi)为6.7，停止透析，并在有ATP或其他核苷酸存在的情况下监测PHi的恢复(增加)，使用氰化物来阻止氧化磷酸化。根据细胞内pH升高速率和细胞内缓冲能力计算当量挤出酸速率(JH)。在实验系列1中，我们使用透析来改变[ATP]i，发现Michaelis-Menten动力学描述JHv。在系列2中，我们检测了ATP−S、AMP-PNP、AMP-PCP、AMP-CPP、GMP-PNP、ADP、ADPβS和μγS，以确定是否有它们自己可以支持运输。只有ATPγS(8 Mm)支持酸挤压；ATPγS还支持Na+驱动的Cl-HCO3交换器所预期的依赖于HCO3−的36Cl外流。最后，在系列3中，我们询问是否有任何核苷酸可以在∼230和μM的背景存在下改变JH(对照JH=111.7PmoL cm−2s−1)。我们发现JH略有下降8 mM AMP-PNP(JH=88.0pmolcm−2s−1)，但适度增加1mmADPβS(JH=916.0pmocm−2s−1)。我们认为，三磷酸腺苷γS导致转运蛋白的稳定磷酸化或一个必要的激活剂。
Squid giant axons recover from acid loads by activating a Na+-driven Cl–HCO3exchanger. We internally dialyzed axons to an intracellular pH (pHi) of 6.7, halted dialysis and monitored the pHirecovery (increase) in the presence of ATP or other nucleotides, using cyanide to block oxidative phosphorylation. We computed the equivalent acid-extrusion rate (JH) from the rate of pHiincrease and intracellular buffering power. In experimental series 1, we used dialysis to vary [ATP]i, finding that Michaelis-Menten kinetics describesJHvs. [ATP]i, with an apparentVmaxof 15.6 pmole cm−2s−1andKmof 124 μM. In series 2, we examined ATPγS, AMP-PNP, AMP-PCP, AMP-CPP, GMP-PNP, ADP, ADPβS and GDPβS to determine if any, by themselves, could support transport. Only ATPγS (8 mM) supported acid extrusion; ATPγS also supported the HCO3−-dependent36Cl efflux expected of a Na+-driven Cl–HCO3exchanger. Finally, in series 3, we asked whether any nucleotide could alterJHin the presence of a background [ATP]iof ∼230 μM (controlJH= 11.7 pmol cm−2s−1). We foundJHwas decreased modestly by 8 mM AMP-PNP (JH= 8.0 pmol cm−2s−1) but increased modestly by 1 mM ADPβS (JH= 16.0 pmol cm−2s−1). We suggest that ATPγS leads to stable phosphorylation of the transporter or an essential activator.