title: Regulation of pH in rat brain synaptosomes. I. Role of sodium, bicarbonate, and potassium.
abstract: 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+).
authors.affiliation: Departamento de Fisiología, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, Mexico.
authors.forename: S
authors.initials: S
authors.lastname: Sánchez-Armass
authors.forename: R
authors.initials: R
authors.lastname: Martínez-Zaguilán
authors.forename: G M
authors.initials: GM
authors.lastname: Martínez
authors.forename: R J
authors.initials: RJ
authors.lastname: Gillies
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001921:Brain / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D009435:Synaptic Transmission / Q000502:physiology; D013574:Synaptosomes / Q000502:physiology*
chemical_list: D001639:Bicarbonates; D002352:Carrier Proteins; D012964:Sodium; D011188:Potassium; D002118:Calcium