Na(+)-dependent Cl-HCO3 exchange in the squid axon. Dependence on extracellular pH.
Na(+)-dependent Cl-HCO3 exchange in the squid axon. Dependence on extracellular pH.
复制标题
DOI：
10.1085/jgp.99.5.817
复制
发表时间：
1992-05
期刊：
影响因子：
--
通讯作者：
Knakal RC
中科院分区：
文献类型：
--
作者：
Boron WF;Knakal RC
鱿鱼巨轴突细胞内pH（pHi）通过Na（+）依赖的Cl-HCO 3交换剂从酸负荷中恢复，其实际机制可能是：（i）外部Na+和HCO 3-交换内部Cl-和H+，（ii）Na+两个HCO 3-交换Cl-，（iii）Na+和CO 3 =交换Cl-，或（iv）NaCO 3-离子对交换Cl-。在这里，我们研究的敏感性的运输细胞外的pH值（pH值）的变化范围在7.1-8.6。我们以四种方式改变pH值，使用：（i）经典的“代谢”干扰，其中我们在固定的[CO 2]o下改变[HCO 3-]o，[NaCO 3-]o和[CO 3 =]o;（ii）经典的“呼吸”干扰，其中我们在固定的[HCO 3-]o下改变[CO 2]o，[NaCO 3-]o和[CO 3 =] o;（iii）新的混合型酸碱紊乱，其中我们在固定的[CO 3 =]o和[NaCO 3-]o下改变[HCO 3-]o和[CO 2]o;（iv）第二系列新的混合型扰动，其中我们在固定的[HCO 3-]o和[NaCO 3-]o下改变[CO2]o、[CO 3 =] o和[Na+]o。轴突（初始pHi约7.4）用含有400 mM Cl-但不含Na+的pH 6.5溶液进行内部透析。在用玻璃微电极测量的pHi降至约6.6后，停止透析。由pHi恢复速率计算当量酸挤出速率（JH）（即，在Na+和HCO 3-存在下，当通过方法（i）改变pH值时（该方法产生最大范围的[CO 3 =]o和[NaCO 3-]o值），JH以S形方式随pH值增加;该关系通过pH滴定曲线拟合，pK约为7.7，希尔系数约为3.0。使用方法（ii），产生较小的变化[CO 3 =]o和[NaCO 3-]o，JH也增加了pH值，但不太陡峭。与方法（iii），既不涉及[CO 3 =]o也不涉及[NaCO 3-]o的变化，JH是不敏感的pH值的变化。最后，在方法（iv）中，既不涉及[HCO 3-]也不涉及[NaCO 3-]o的变化，但涉及[CO 3 =]o和[Na+]o的相互变化，JH对pH值变化也不敏感。我们发现，降低pH值从8.6到7.1引起的表观Km外部HCO 3-（[Na+]o = 425 mM）从1.0增加到26.7 mM，而Jmax是相对稳定的。将pH从8.6降低到7.4导致外部Na+（[HCO 3-]o = 48 mM）的表观Km值从8.6增加到81 mM，而Jmax相对稳定。（400字处截断摘要）
Intracellular pH (pHi) in squid giant axons recovers from acid loads by means of a Na(+)-dependent Cl-HCO3 exchanger, the actual mechanism of which might be exchange of: (i) external Na+ and HCO3- for internal Cl- and H+, (ii) Na+ plus two HCO3- for Cl-, (iii) Na+ and CO3= for Cl-, or (iv) the NaCO3- ion pair for Cl-. Here we examine sensitivity of transport to changes of extracellular pH (pHo) in the range 7.1-8.6. We altered pHo in four ways, using: (i) classical "metabolic" disturbances in which we varied [HCO3-]o, [NaCO3-]o, and [CO3=]o at a fixed [CO2]o; (ii) classical "respiratory" disturbances in which we varied [CO2]o, [NaCO3-]o, and [CO3=]o at a fixed [HCO3-]o; (iii) novel mixed-type acid- base disturbances in which we varied [HCO3-]o and [CO2]o at a fixed [CO3=]o and [NaCO3-]o; and (iv) a second series of novel mixed-type disturbances in which we varied [CO2]o, [CO3=]o, and [Na+]o at a fixed [HCO3-]o and [NaCO3-]o. Axons (initial pHi approximately 7.4) were internally dialyzed with a pH 6.5 solution containing 400 mM Cl- but no Na+. After pHi, measured with a glass microelectrode, had fallen to approximately 6.6, dialysis was halted. The equivalent acid extrusion rate (JH) was computed from the rate of pHi recovery (i.e., increase) in the presence of Na+ and HCO3-. When pHo was varied by method (i), which produced the greatest range of [CO3=]o and [NaCO3-]o values, JH increased with pHo in a sigmoidal fashion; the relation was fitted by a pH titration curve with a pK of approximately 7.7 and a Hill coefficient of approximately 3.0. With method (ii), which produced smaller changes in [CO3=]o and [NaCO3-]o, JH also increased with pHo, though less steeply. With method (iii), which involved changes in neither [CO3=]o nor [NaCO3-]o, JH was insensitive to pHo changes. Finally, with method (iv), which involved changes in neither [HCO3-] nor [NaCO3-]o, but reciprocal changes in [CO3=]o and [Na+]o, JH also was insensitive to pHo changes. We found that decreasing pHo from 8.6 to 7.1 caused the apparent Km for external HCO3- ([Na+]o = 425 mM) to increase from 1.0 to 26.7 mM, whereas Jmax was relatively stable. Decreasing pHo from 8.6 to 7.4 caused the apparent Km values for external Na+ ([HCO3-]o = 48 mM) to increase from 8.6 to 81 mM, whereas Jmax was relatively stable.(ABSTRACT TRUNCATED AT 400 WORDS)