Summary: Effects of severe lactacidosis were analyzed in vitro by employment of C6 glioma cells and astrocytes from primary culture. The cells were suspended in a physiological medium, which was rendered acidotic by addition of lactic acid in rising concentrations. A pH range of 7.4-4.2 was studied under maintenance of isoto nicity and a normal electrolyte concentration of the me dium. Cell swelling was quantified by flow cytometry us ing an advanced Coulter system with hydrodynamic fo cusing. The method was also utilized for assessment of cell viability by exclusion of the fluorescent dye propid ium iodide. The volume of C6 glioma cells was found to increase if the pH was titrated to pH 6.8 or below. From this level downward, the extent of cell swelling depended on the degree of acidosis and the duration of exposure. For example, lactacidosis of pH 6.2 for 60 min led to an increase in cell size to 124.5% of normal, while pH 5.0 or 4.2 led to a cell size of 151.1 or 190.9%, respectively. A comparative analysis of the acidosis-induced cell swelling was made by using sulfuric acid. Swelling of C6 glioma at a given pH was only half of what was found when using lactic acid. This indicates specific swelling-inducing prop erties of lactic acid, while cell viability was not differently affected by both acids. Of the C6 glioma cells, 89.1 % were viable under control conditions at pH 7.4. The via bility remained unchanged down to pH 6.2. At pH 5.6, viability remained normal for 30 min, but it decreased to 73.4% after 60 min. Further lowering of pH to 5.0 or 4.6 respectively, decreased the number of viable cells to 47.8 Cerebral ischemia, seizures, and severe head in jury are associated with an enhancement of anaer obic metabolism resulting in intra-and extracellular lactacidosis (Siesj6, 198 1, 1988). Lactacidosis may be involved in the formation of cytotoxic brain edema and irreversible damage of nerve and glial

Xe blocks not only NMDA receptors, but also AMPA and kainate receptors in cortical neurones as well as GluR6-type receptors expressed in SH-SY5Y cells. Thus, Xe seems to be rather non-specific as a channel blocker and this may contribute to the analgesic and anaesthetic potency of Xe.

Unlike hydrocarbon-based gaseous anesthetics, Xe does not significantly alter any measured electrical, mechanical, or metabolic factors, or the nitric oxide-dependent flow response in isolated hearts, at least partly because Xe does not alter the major cation currents as shown here for cardiac myocytes. The authors' results indicate that Xe, at approximately 1 MAC for humans, has no physiologically important effects on the guinea pig heart.

Background and purpose:There is increasing evidence that not only the monoaminergic but also the glutamatergic system is involved in the pathophysiology of attention-deficit hyperactivity disorder (ADHD). Hyperactivity of glutamate metabolism might be causally related to a hypoactive state in the dopaminergic system. Atomoxetine, a selective noradrenaline reuptake inhibitor, is the first non-stimulant approved for the treatment of this disorder. Here we have evaluated the effects of atomoxetine on glutamate receptors in vitro. Experimental approach: The whole-cell configuration of the patch-clamp technique was used to analyse the effect of atomoxetine on N-methyl-D-aspartate (NMDA) receptors in cultured rodent cortical and hippocampal neurons as well as on NMDA receptors heterologously expressed in human TsA cells. Key results: Atomoxetine blocked NMDA-induced membrane currents. Half-maximal inhibition emerged at about 3 mM which is in the range of clinically relevant concentrations found in plasma of patients treated with this drug. The inhibition was voltage-dependent, indicating an open-channel blocking mechanism. Furthermore, the inhibitory potency of atomoxetine did not vary when measured on NMDA receptors from different brain regions or with different subunit compositions. Conclusions and implications:The effective NMDA receptor antagonism by atomoxetine at low micromolar concentrations may be relevant to its clinical effects in the treatment of ADHD. Our data provide further evidence that altered glutamatergic transmission might play a role in ADHD pathophysiology.

Glutamate is the main excitatory neurotransmitter in the vertebrate central nervous system. Removal of this transmitter from the synaptic cleft by glial and neuronal transporter systems plays an important role in terminating glutamatergic neurotransmission. The effects of different activators and blockers of PKA and PKC on glutamate uptake were studied in primary glial cells cultivated from the rat cortex using the patch-clamp recording technique and immunocytochemical methods. GF 109203X enhances glutamate-induced membrane currents in a concentration- and time-dependent manner. After pre-application for 40 s the maximal transport capacity was increased by 30-80%. The estimated Km-value of the transport system did not change after drug application and the enhanced glutamate uptake was reversible within a few minutes upon washout. Activators and blockers of the PKC pathway did not affect glutamate uptake, whereas H89, a selective blocker of PKA, mimicked the effects of GF 109203X, indicating involvement of the protein kinase A pathway. The GF 109203X-induced increase in transport capacity is likely to be mediated by GLAST since the GLT-1 selective blocker dihydrokainate was unable to block basal or stimulated glutamate uptake. Furthermore, the increase in transport activity may well be based on an increase in cell surface expression of the transporter protein since preincubation with cytochalasin-B, a protein that blocks actin polymerization, almost completely abolished the effect of GF 109203X and H89. These results indicate that GF 109203X and H89 enhance glial glutamate uptake via blockade of the PKA. The described effect may affect glutamatergic neurotransmission by reducing the glutamate concentration in the synaptic cleft.