Regulation of pH in rat brain synaptosomes. I. Role of sodium, bicarbonate, and potassium.
Regulation of pH in rat brain synaptosomes. I. Role of sodium, bicarbonate, and potassium.
复制标题
大鼠脑突触体 pH 值的调节。
DOI：
10.1152/jn.1994.71.6.2236
复制
发表时间：
1994
影响因子：
2.5
通讯作者：
Gillies,RJ
中科院分区：
文献类型：
--
作者：
Sanchez-Armass,S;Martinez-Zaguilan,R;Martinez,GM;Gillies,RJ
1.利用荧光pH指示剂和时间分辨荧光光谱技术，研究了大鼠脑内神经末梢(突触体)细胞内pH的调节。2.HCO3-的存在或不存在对静息pH i无显著影响。在无HCO3-或有HCO3-存在的情况下，去除外部Na+会导致PHi迅速酸化。酸负荷的恢复主要是由于Na+/H+交换的活性，证实了这一运输系统在突触体中的相关性。3.在突触体中，Na~+/H~+交换器的活性不受蛋白激酶C和蛋白激酶A的调节，相反，Ca~(2+)在Na~+/H~+交换器的调节中起重要作用。观察到4BR-A23187诱导了依赖于Na(+)的静息pH碱化，并极大地提高了初始速率和从酸负荷中恢复的程度。4.在大多数真核细胞中，基于HCO3(-)的转运机制在phi调节中起着重要作用。然而，在突触体中，HCO3-转运并不显著地参与Phi的调节，因为HCO3-的存在或不存在不会影响静息Phi，也不会影响Phi对酸负荷的恢复速度。本文还讨论了氯离子和HCO3-在突触体PHI调节中的作用。5.随着KO+浓度的增加，稳态pH i升高，这一过程不依赖于Ca~(2+)和HCO_3。这种碱化可能是由于K+/H+交换活性、K(+)诱导的去极化、Delta microH+的减少或Delta microK+的直接还原所致。计算的H+驱动力表明，内向H+泄漏的减少足以解释K(+)诱导的碱化，因为它通过将膜电位差(Em)设置为K+平衡电位(EK+)来改变增量微H+。
1. We investigated the regulation of intracellular pH (pHi) in rat brain isolated nerve terminals (synaptosomes), using fluorescence pH indicators and time-resolved fluorescence spectroscopy. 2. The resting pHi was not significantly affected by the presence or absence of HCO3-. Removal of external Na+, in the absence or presence of HCO3- caused a rapid acidification of pHi. The recovery from acid loads was primarily due to the activity of the Na+/H+ exchanger, confirming the relevance of this transport system in synaptosomes. 3. Our data revealed that in synaptosomes the activity of the Na+/H+ exchanger was not regulated by either protein kinase C or kinase A. In contrast, Ca2+ played an important role in the regulation of Na+/H+ exchanger. This was supported by the observation that 4Br-A23187 induced a Na(+)-dependent alkalinization of the resting pHi and greatly enhanced the initial rate and the degree of the recovery from acid loads. 4. In most eukaryotic cells, HCO3(-)-based transport mechanisms play an important role in pHi regulation. In synaptosomes, however, HCO3- transport is not significantly involved in pHi regulation, because the presence or absence of HCO3- does not affect resting pHi nor the rate of pHi recovery to acid loads. Further studies to address the role of Cl- and HCO3- in pHi regulation in synaptosomes are discussed in the companion paper. 5. Increasing the concentration of Ko+ also resulted in a rise of steady-state pHi by a processes that is Ca2+ and HCO3- independent. This alkalinization could be due to either K+/H+ exchanger activity, K(+)-induced depolarization, reduction of delta microH+, or a direct reduction of delta microK+. Calculated H+ driving forces suggest that the reduction in the inwardly directed H+ leak is sufficient to explain this K(+)-induced alkalinization because it changes the delta microH+ by virtue of setting the membrane potential difference (Em) to the K+ equilibrium potential (EK+).