pH-dependent inhibition of native GABA(A) receptors by HEPES.

BACKGROUND AND PURPOSE: Artificial buffers such as HEPES are extensively used to control extracellular pH (pH(e) ) to investigate the effect of H(+) ions on GABA(A) receptor function. EXPERIMENTAL APPROACH: In neurones cultured from spinal cord dorsal horn (DH), dorsal root ganglia (DRG) and cerebellar granule cells (GC) of neonatal rats, we studied the effect of pH(e) on currents induced by GABA(A) receptor agonists, controlling pH(e) with HCO(3) (-) or different concentrations of HEPES. KEY RESULTS: Changing HEPES concentration from 1 to 20 mM at constant pH(e) strongly inhibited the currents induced by submaximal GABA applications, but not those induced by glycine or glutamate, on DH, DRG or GC neurones, increasing twofold the EC(50) for GABA in DH neurones and GC. Submaximal GABA(A) receptor-mediated currents were also inhibited by piperazine-N,N'-bis(2-ethanesulfonic acid) (PIPES), 3-(N-morpholino)propanesulfonic acid, tris(hydroxymethyl)aminomethane or imidazole. PIPES and HEPES, both piperazine derivatives, similarly inhibited GABA(A) receptors, whereas the other buffers had weaker effects and 2-(N-morpholino)ethanesulfonic acid had no effect. HEPES-induced inhibition of submaximal GABA(A) receptor-mediated currents was unaffected by diethylpyrocarbonate, a histidine-modifying reagent. HEPES-induced inhibition of GABA(A) receptors was independent of membrane potential, HCO(3) (-) and intracellular Cl(-) concentration and was not modified by flumazenil, which blocks the benzodiazepine binding site. However, it strongly depended on pH(e) . CONCLUSIONS AND IMPLICATIONS: Inhibition of GABA(A) receptors by HEPES depended on pH(e) , leading to an apparent H(+) -induced inhibition of DH GABA(A) receptors, unrelated to the pH sensitivity of these receptors in both low and physiological buffering conditions, suggesting that protonated HEPES caused this inhibition.

Stimulation of serotonin2C receptors elicits abnormal oral movements by acting on pathways other than the sensorimotor one in the rat basal ganglia.

Serotonin2C (5-HT(2C)) receptors act in the basal ganglia, a group of sub-cortical structures involved in motor behavior, where they are thought to modulate oral activity and participate in iatrogenic motor side-effects in Parkinson's disease and Schizophrenia. Whether abnormal movements initiated by 5-HT(2C) receptors are directly consequent to dysfunctions of the motor circuit is uncertain. In the present study, we combined behavioral, immunohistochemical and extracellular single-cell recordings approaches in rats to investigate the effect of the 5-HT(2C) agonist Ro-60-0175 respectively on orofacial dyskinesia, the expression of the marker of neuronal activity c-Fos in basal ganglia and the electrophysiological activity of substantia nigra pars reticulata (SNr) neuron connected to the orofacial motor cortex (OfMC) or the medial prefrontal cortex (mPFC). The results show that Ro-60-0175 (1 mg/kg) caused bouts of orofacial movements that were suppressed by the 5-HT(2C) antagonist SB-243213 (1 mg/kg). Ro-60-0175 (0.3, 1, 3 mg/kg) dose-dependently enhanced Fos expression in the striatum and the nucleus accumbens. At the highest dose, it enhanced Fos expression in the subthalamic nucleus, the SNr and the entopeduncular nucleus but not in the external globus pallidus. However, the effect of Ro-60-0175 was mainly associated with associative/limbic regions of basal ganglia whereas subregions of basal ganglia corresponding to sensorimotor territories were devoid of Fos labeling. Ro-60-0175 (1-3 mg/kg) did not affect the electrophysiological activity of SNr neurons connected to the OfMC nor their excitatory-inhibitory-excitatory responses to the OfMC electrical stimulation. Conversely, Ro-60-0175 (1 mg/kg) enhanced the late excitatory response of SNr neurons evoked by the mPFC electrical stimulation. These results suggest that oral dyskinesia induced by 5-HT(2C) agonists are not restricted to aberrant signalling in the orofacial motor circuit and demonstrate discrete modifications in associative territories.

[Apolipoprotein E and angiotensin-converting enzyme gene polymorphisms as risk factors of coronary disease]. / Implication du polymorphisme génétique de l'apolipoprotéine E et de l'enzyme de converstion de l'angiotensine dans l'athérosclérose coronarienne.

The objective of this study was to test the hypothesis that apo E (RFLP, HhaI) and/or angiotensin-converting enzyme (ACE) (ins16del) are associated with higher risk for coronary heart disease. We investigated 250 patients who underwent complete cardiac examination comprising coronary angioplasty and biological analysis (CT, HDLc, LDLc, TG, apo A and apo B). Prevalence of the alleles of apo E and ACE was assessed by molecular analysis. Patients without stenosis or with non-significant stenosis (> 50% of the vascular lumen) were used as reference group (141 patients). Those presenting a significant stenosis of the coronary artery (. 50% of the vascular lumen) were considered as cases (109 patients). The relative frequency of the e 4 allele was significantly higher in cases than in reference group (p > 0.02). A strong association have been found between coronary heart disease and apo E polymorphism (2 = 8.91; p > 0.05). The presence of the e 4 allele increase the risk of atherosclerosis (RR = 2.71; IC95%: 1.25-5.90; p > 0.02) compared to e 3 allele. Also, subjects with D allele were more frequent in cases than in reference group (p > 0.001). A significant association was noted between ACE polymorphism and coronary heart disease (2 = 42.15; p > 0.001). This relationship was positive (rho de Spearman = 0.39; p > 0.01). With D/D homozygotes patients, the RR for coronary heart disease was 19.10 (p > 0.001), while The RR with I/D heterozygotes was 6.91 (p > 0.001) compared to I/I homozygotes. A significant interaction have been shown up between D/D genotype and arterial hypertension (HTA) (2 de Wald = 16.10; p > 0.001). The multivariate analysis showed that the chronic smoking, diabetes, hypoapolipoproteinemia A, interactive effects between D/D and HTA, I/D and obesity, and between D/D and hypertriglyceridemia were the major significant factors to take into consideration in our population. We also note that subjects with both D and e 4 alleles were presenting a high risk to coronary heart disease (RR = 5.93; IC95%: 2.00-17.55; p > 0.01). Thus, those two alleles (4 and D) appears to be important cardiovascular risk factors in the moroccan population.

[Homocysteine, lipoprotein (a): risk factors for coronary heart disease]. / Homocystéine, lipoprotéine (a): acteurs de risque de l'athérosclérose coronarienne.

Our data suggest that the hyperhomocysteinemia and/or increased plasma level of lipoprotein Lp(a) are risk factors for coronary heart disease. We investigated 178 patients who underwent complete cardiac examination comprising coronary angiography and biological analysis (CT, HDL-c, LDL-c, TG, and apoAI, apoB, homocysteine and Lp(a)). Patients presenting a significant stenosis of the coronary artery ( 50% of the vascular lumen) were considered as cases (113 patients). Those without stenosis or with non-significant stenosis (< 50% of the vascular lumen) were used as controls (65 subjects). Homocysteinemia was significantly higher in cases than in control subjects (8.26 mol/L (2.34 versus 17.85 (2.34, p < 0.001). A strong association between coronary heart disease and homocystein has been found (Eta(2) = 0.76). The OR were 0.16 when homocystein level was lower than 15 mol/L, and 27.78 when homocysteine level was upper than or equal to 15 mol/L. The RR was 5.16 (95% IC = 3.66-6.66, p < 0.001). Even though there was a significant correlation between tabagic impregnation and homocysteinemia (Spermann's rho = 0.37, p < 0.05), there was no interactive effect between these two factors and coronary disease (Wald khi2 = 0.086, p > 0.05). Therefore, no association was found between homocyteinemia and other coronary heart disease risk factors. The Lp(a) levels were significantly higher in cases than in controls subjects (188 (84 mg/L in control subjects versus 590 (199 in cases, p < 0.001). A stronger relationship was noted between coronary heart disease and Lp(a) (Eta (2) = 0.66). The OR were 0.09 when lipoprotein (a) levels were lower than 350 mg/L, and 5,88 when Lp(a) levels were higher than or equal to 350 mg/L. The estimate RR was 6.47 (95% IC = 4.39-8.55, p < 0.001). The level of Lp(a) was positively correlated with the severity of coronary heart disease (Spermann's rho = 0.95, p < 0.001). A weak correlation between Lp(a) and LDL-c was observed (Spermann's rho = 0.12, p = 0.048). But the multivariate analysis didn't show interactive effect between these two factors and coronary disease (khi2 de Wald = 0.264, p > 0.05). No association was noted between Lp(a) and the others risk factors. Moreover, a positive correlation between the levels of homocysteine and those of Lp(a) was found (Spermann's rho = 0.54, p < 0.001). In contrast their effect on coronary heart disease seems to be independant (Wald khi2 = 2.957, p > 0.05). Thus, these two parameters appear as independant risk factors for coronary heart disease.