Effect of lactic and CO2 acidosis on neuronal function following glucose-oxygen deprivation in rat hippocampal slices

Synaptic depression and neuronal loss in transiently acidic hippocampal slice cultures

Acidosis is a rapid and inevitable event accompanying cerebral ischemia or trauma. We used hippocampal slice cultures to examine an immediate effect of acidosis, synaptic depression; and a delayed effect, neuronal loss. Exposure to low bicarbonate artificial cerebral spinal fluid (aCSF), pH 6.70 for 30 min at 32 degrees C, acidified intracellular pH from 7.31+/-0.12 to 6.53+/-0.08. Accompanying intracellular acidosis was a depression of synaptic responses. Both effects rapidly reversed after treatment with normal aCSF pH 7.35. Death analysis after acidosis treatment revealed no delayed neuronal loss. Increasing the duration of the acidosis to 60 min, however, induced irreversible synaptic depression and delayed neuronal loss. Increasing acidosis temperature to 37 degrees C acidified intracellular pH and depressed synaptic responses. Delayed neuronal loss was also observed. Acidosis using lactate aCSF, pH 6. 70 for 30 min at 32 degrees C acidified intracellular pH from 7. 19+/-0.13 to 6.43+/-0.07 and depressed synaptic responses. After reperfusion with lactate containing aCSF pH 7.35, intracellular pH recovered yet synaptic responses remained depressed and delayed neuronal loss was observed. This suggested that, for a 30-min treatment at 32 degrees C, lactate acidosis was neurotoxic while low bicarbonate acidosis was not. Increasing the duration or temperature of low bicarbonate acidosis induced neuronal loss. These data provide additional evidence that acidosis contributes to the neurotoxicity during stroke and trauma.

Effects of stobadine, melatonin, and other antioxidants on hypoxia/reoxygenation-induced synaptic transmission failure in rat hippocampal slices

In vitro reversible ischemia was simulated with rat hippocampal slices in order to test the neuroprotective activity of selected antioxidants with emphasis on the pyridoindole stobadine. Slices were exposed to hypoxia (HYP) combined with lowered D-glucose concentration to induce synaptic transmission (ST) failure, which turned out to be irreversible in approximately 80%-100% of slices during reoxygenation (ROX). The amplitude of population spikes (PoS) evoked trans-synaptically by electrical stimulation of Schäffer collaterals and recorded in CA1 neurons was the parameter of ST. Pretreatment of slices with stobadine dissolved in slice superfusion media (1 to 100 microM) improved ST recovery after 20-min tissue ROX. Stobadine decreased the number of irreversibly damaged slices and increased the average amplitude of PoS during tissue ROX. The concentration-response relationship of protective activity was bell-shaped, with maximum at 3-30 microM. Moreover, the half-time of PoS decay (t1/2) during HYP was significantly delayed in stobadine treated groups (10 to 100 microM). The neurohormone melatonin (30 to 100 microM) and 21-aminosteroid U-74389G (10 microM) revealed similar protective activity on ST recovery and on t1/2 during HYP. Trolox (200 microM) improved the PoS recovery, yet it had no effect on t1/2. The iron chelator deferoxamine (250 and 500 microM) had no protective effects at all. alpha-Tocopherol administered to animals orally (200 mg/kg for 10 days) only marginally improved the PoS recovery. Comparing the protective effect of compounds tested on PoS recovery, we assume the following rank order of potency: U-74389G > stobadine > melatonin >> trolox. Our findings suggest that stobadine as well as trolox, U-74389G and melatonin, antioxidants with remarkably different chemical structures, exerted neuroprotective activity, probably determined by antioxidative properties of these compounds. Moreover, stobadine, U-74389G, and melatonin were able to delay the early ST decay during HYP, which might indicate improved energetic state of neurons in the treated tissue. The study supports the notion about the neuroprotective activity of certain antioxidants.

Extracellular dopamine and catabolites in rat striatum during lactic acid perfusion as determined by in vivo microdialysis

Many experimental studies concerning hypoxia or ischemia have reported a decrease in intra/extracellular pH and massive dopamine (DA) release in the striatum. The present work investigated whether the increase in striatal extracellular DA is related to acidification or to lactate production. Striatal perfusion of lactic acid (pH 5.5) by microdialysis in conscious freely-moving rats induced an increase in extracellular concentrations of DA and catabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), as a probable result of acidification. Perfusion with sodium lactate (pH 7.4) failed to modify DA and catabolite release, whereas orthophosphoric acid produced the same effect as lactic acid. As lactic acidosis is known to induce a displacement of iron from its uptake sites, the possible role of this metal in response to acidosis was studied by perfusing ferrozine, an iron complexing agent, at the same time as lactic acid. The results showed that ferrous ions are involved in the process and suggested that oxygen free radicals play a role in the extracellular release of DA. Thus, lactic acid perfusion in rat striatum would appear to be a useful model for in vivo studies of the mechanisms responsible for increases in extracellular DA during hypoxia and ischemia.

Extracellular acidosis delays cell death against glucose-oxygen deprivation in neuroblastoma x glioma hybrid cells

OBJECTIVE

To determine whether extracellular acidosis delays cell death against glucose-oxygen deprivation and, if so, whether this result is due to inhibition of calcium (Ca2+) influx or preservation of cellular energy state.

DESIGN

Randomized, controlled, prospective study.

SETTING

University research laboratory.

SUBJECTS

Differentiated neuroblastoma x glioma NG108-15 cells.

INTERVENTIONS

Experiment 1: cells were incubated for 8 hrs in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid-buffered medium under glucose-oxygen deprivation at pH 7.4, 6.8, 6.5, 6.2, 5.6, or 5.0. Experiment 2: cells were incubated for 8 hrs under glucose-oxygen deprivation after excluding extracellular calcium from culture medium at pH 7.4 or 6.2. Experiment 3: cells were incubated for 2, 4, 6, or 8 hrs in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid-buffered medium under glucose-oxygen deprivation at pH 7.4 or 6.2 and assayed for high-energy phosphates.

MEASUREMENTS AND MAIN RESULTS

Cell viability was measured with flow cytometry after the cells were stained with fluorescein diacetate and propidium iodide. Cellular adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate were analyzed with high-performance liquid chromatography. Cell viability was significantly greater at pH 6.2 than at pH 7.4 in experiment 1. By excluding extracellular calcium, a significant difference in viability between pH 7.4 and 6.2 persisted in experiment 2. Energy charge and the concentration of adenosine triphosphate were significantly greater at pH 6.2 than at pH 7.4 in the intervals preceding manifestation of a differential effect of acidosis on cell viability in experiment 3.

CONCLUSIONS

Extracellular acidosis at pH 6.2 delayed cell death against glucose-oxygen deprivation. This protective effect by extracellular acidosis may be due to preservation of the cellular energy state in NG108-15 cells, although this study does not exclude the possibility that in other cell types, inhibition of calcium influx may have an effect.

Mechanism of cellular swelling induced by extracellular lactic acidosis in neuroblastoma-glioma hybrid (NG108-15) cells

The mechanism of cellular swelling induced by extra-cellular lactic acidosis and the effect of diuretics were studied using neuroblastoma-glioma hybrid (NG108-15) cells. The cells were incubated in one of three lactate concentrations (0, 15, or 30 mM), each of which was randomized to one of three pH groups (7.4, 6.2, or 5.0). Analysis of the swelling was measured using a Coulter counter technique. Cellular swelling was most prominent at pH 6.2 at all lactate levels. Cellular swelling was noted to be pH dependent but not lactate dependent. The addition of 1 mM amiloride completely blocked cellular swelling, suggesting that the main mechanism of neuronal cellular swelling induced by extracellular lactic acidosis was the activation of Na+/H+ exchange. Second, three dissimilar diuretic drugs were used for cellular swelling: amiloride (Na+/H+ exchange inhibitor), mannitol (osmotic diuretic), and bumetanide (loop diuretic). Amiloride and mannitol were found effective in reducing the lactic acidosis-induced cellular swelling. Furthermore, the combination of these drugs had additive effects. However, bumetanide was not effective. The results indicate that the direct inhibition of Na+/H+ exchange and/or removal of water from the cell by mannitol was effective against cellular swelling induced by the activation of Na+/H+ exchange in NG108-15 cells.