Intracellular pH regulation in cultured mouse oligodendrocytes.

Abstract

SUMMARY1. Intracellular pH (pHi) and the mechanism of pHi regulation have been investigated in cultured oligodendrocytes from mouse spinal cord using doublebarrelled neutral-carrier H+-selective microelectrodes. The distribution of H+ was not in electrochemical equilibrium. The pHi was more alkaline than the pH of the bathing medium (pHO), namely 7-5 at pHo 7-2 and 7-6 at pHo 7-4. 2. Removal of HCO3-from the bathing medium reduced the steady-state pHi by 0 4 units. An increase in extracellular K+ caused, with a delay, an increase in pHi. A decrease in pHO to 6-2 caused an acidification of pHi by 0 5 units.3. The pHi regulation was studied by applying and subsequently removing NH4, which resulted in an acidification of the cell. The subsequent recovery of pHi could then be analysed. The recovery from an acidification by 1 pH unit lasted 3-10 min.In HCO3--free solution pHi recovery was slowed. 4. In HCO3--free solution pHi recovery was completely blocked when either Na+ was removed or when amiloride was applied indicating an exclusive activation of the Na+-H+ exchanger.5. In the presence of HCO3 , removal of Na+ also completely blocked pH1 recovery. When Na+ was readded, pHi recovered. In HCO3--containing solution amiloride slightly slowed, but did not block pHi recovery.6. Removal of Cl-or application of SITS, DIDS or furosemide, blockers of Cl--coupled transport mechanisms, did not affect the pHi recovery in the presence of HCO3-.7. In conclusion, oligodendrocytes possess two mechanisms regulating pHi, a Na+-H+ exchanger and a Na+-HCO3-co-transporter while the latter is clearly more potent. It follows that pHi regulation of oligodendrocytes is dependent on the transmembrane Na+ gradient and is strictly separated from regulation of internal Cl.

Regulation of Intracellular pH in Single Rat Cortical Neurons in vitro: A Microspectrofluorometric Study

“…Although not examined in any detail, similar results were reported in rat superior cervical ganglion cells (Tolkovsky and Richards, 1987) and rat brain syn aptosomes (Nachsen and Drapeau, 1988). Similar observations have also been made in other cells (L' Allemain et aI., 1984;Moolenaar and Tertoolen, 1984;Kettenmann and Schlue, 1988) . It has gener ally been assumed that the important variable reg ulating the rate of H+ extrusion is pHi' The strong correlation between pHe and pHi challenges this no tion and raises the question of whether the H+ ex trusion mechanisms are relatively feeble compared to the leak pathways available or whether the reg ulatory parameter is another one, such as the trans membrane H + gradient.…”

Intracellular acidification by inhibition of the Na+/H+-exchanger leads to caspase-independent death of cerebellar granule neurons resembling paraptosis

“…Increasing or decreasing extracellular pH by 1 unit is followed by an increase or decrease of intracellular pH by 0.5 units in murine cortical neurons. 25,26 Likewise, increasing the extracellular pH of cerebellar granule neurons by 0.3 units caused an increase in pH i by about 0.15 units (Figure 3a). We now investigated if counteracting intracellular acidification by alkalizing the culture medium would prevent death induced by potassium withdrawal or blocking the NHE.…”

Ionic Transporter Activity in Astrocytes, Microglia, and Oligodendrocytes During Brain Ischemia

“…À mechanism, which mediates the influx of HCO3 À ions into the cell, is involved in pH i homeostasis of cultured OLGs from embryonic mouse spinal cord 125 and adult rat cerebellum. 84 In the presence of external bicarbonate/CO 2 , resting pH i is not modified by the removal of external chloride, or by blockers of the chloride-coupled transport Cl À /HCO3 À systems.…”