Differential effects of the pyrethroid tetramethrin on tetrodotoxin-sensitive and tetrodotoxin-resistant single sodium channels

The differential effects of the pyrethroid tetramethrin on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) single sodium channel currents in rat dorsal root ganglion (DRG) neurons were investigated using the outside-out configuration of patch-clamp technique. Channel conductances were 10.7 and 6.3 pS for TTX-S and TTX-R sodium channels, respectively, at a room temperature of 24–26°C. The single-channel current of TTX-S sodium channels at the test potential of −30 mV was −1.27 ± 0.25 pA, and was not changed after exposure to 10 μM tetramethrin (−1.28 ± 0.23 pA). The open time histogram of TTX-S single-channel currents could be fitted by a single exponential function with a time constant of 1.27 ms. After exposure to 10 μM tetramethrin, the open time histogram could be fitted by the sum of two exponential functions with time constants of 1.36 ms (τ_fast) and 5.73 ms (τ_low). The percentage of contribution of each component to the population was 62% for the fast component representing the normal channels and 38% for the slow component representing the tetramethrin modified channels. The amplitudc of TTX-R single-channel currents was slightly changed from −0.72 ± 0.14 to −0.83 ± 0.07 pA by 10 μM tetramethrin. The open time histogram of TTX-R single-channel currents could be fitted by a single exponential function with a time constant of 1.92 ms. In the presence of 10 μM tetramethrin, the open time histogram could be fitted by the sum of two exponential functions with time constants of 2.07 ms (τ_fast) and 9.75 ms (τ_slow). The percentage of contribution of each component was 15% for the fast, unmodified component and 85% for the slow, modified component. Differential effects of tetramethrin on the open time distribution of single sodium channel currents explains the differential sensitivity of TTX-S and TTX-R sodium channels.     

Cerebral sodium sensors in the sodium-deplete sheep

The sodium intake of sodium deplete sheep was studied during local, push-pull perfusion of different solutions within the third cerebral ventricle. Sheep were made sodium deplete by continuous loss of parotid saliva, and were allowed access to 0.6 M NaHCO₃ solution for 2 h daily. Local perfusion within the third cerebral ventricle was performed before and during the access to sodium solution. Four perfusion sites were used: anterior dorsal and ventral, and posterior dorsal and ventral. Perfusion of 200 mM Na-csf caused a decrease in sodium intake at each perfusion site. Perfusion of ouabain, 10⁻⁶M, caused a reduction in sodium intake only during perfusions within the anterior portion of the third ventricle. The results may indicate that specific neuronal elements sensitive to changes in intracellular sodium concentrations are located around the anterior portion of the third cerebral ventricle. These neurones, however, are not exclusive sites from where sodium intake of sodium deplete sheep can be influenced.     

孟鲁斯特对哮喘模型IL-5mRNA和IL-5蛋白表达的影响

目的 探讨白三烯受体拮抗剂孟鲁斯特(MK)对哮喘小鼠IL-5mRNA、IL-5蛋白表达的影响。方法 采用原位杂交、免疫组化LSAB法,检测哮喘小鼠及孟鲁斯特治疗后哮喘小鼠骨髓细胞IL-5mRNA的表达及肺、骨髓、脾IL-5蛋白的表达情况。 结果 孟鲁斯特可显著减轻哮喘小鼠肺组织炎症细胞浸润、细支气管痉挛、粘液分泌等;亦可减少骨髓IL-5mRNA阳性细胞数(P<0.02),并使骨髓、肺、脾IL-5蛋白表达下降。 结论 白三烯受体拮抗剂孟鲁斯特不仅使肺部炎症显著减轻,也抑制骨髓细胞表达IL-5mRNA、IL-5蛋白,提示白三烯可能通过调节炎症细胞、细胞因子合成来应答过敏原反应。     

Expression of Fos in rat brain in relation to sodium appetite: furosemide and cerebroventricular renin

Two experiments were performed to investigate the relationship between the expression of sodium appetite and the appearance of Fos-like immunoreactivity (Fos-IR) in the brain of rats. In the first experiment, rats were depleted of sodium by treatment with furosemide 24 h prior to sacrifice and without access to either food or sodium solution. Some rats had access to distilled water, and others had no fluids available during the 24 h. All of the furosemide-treated rats showed Fos-IR in both the subfornical organ (SFO) and around the organum vasculosum laminae terminalis (OVLT). Rats with access to distilled water during the depletion period showed no Fos-IR in the supraoptic (SON) or paraventricular hypothalamic nuclei (PVN) and, in parallel behavioral studies, comparably-treated rats consumed only 0.3 M NaCl solution at the end of the 24 h. In rats that had no fluids during the deprivation period, only about one half showed Fos-IR in SON and PVN and, in parallel behavioral studies, comparably treated rats consumed both water and 0.3 M NaCI solution at the end of 24 h. In a second experiment, cerebroventricular administration of renin stimulated short latency intake of 0.3 M NaCI and water. The relative intakes of water and NaCl were comparable at a low dose of renin, but intake of water exceeded that of NaCl after higher doses. Renin induced Fos-IR in SFO, MnPO, peri-OVLT region, SON and PVN. Both Fos-IR and fluid intake were antagonized by administration of losartan, an angiotensin 11 type 1 receptor antagonist. Thus, only the circumventricular organs of the lamina terminalis showed Fos-IR during each natriorexigenic regimen in these studies. These data support the view that Ang 11 of both central and peripheral origin activates the SFO and/or peri-OVLT region and contributes to sodium appetite.     

背根神经节Nav1.8磷酸化在大鼠糖尿病痛性周围神经病变中的作用

目的 本研究采用射频热凝毁损腰交感神经节,探讨背根神经节（DRG）Nav1．8磷酸化在大鼠糖尿病痛性周围神经病变中的作用。方法 采用腹腔注射链尿佐菌素诱导糖尿病痛性周围神经病变大鼠模型,取造模成功的大鼠20只,随机分为糖尿病对照组（D组）及交感神经节射频热凝组（R组）,每组10只,另取10只同月龄大鼠为正常对照组（C组）。R组大鼠在X光机介导下行右侧L3,4椎旁腰交感神经节射频热凝毁损。分别于射频热凝前、射频热凝后1、2周时,采用von Frey纤维丝测定大鼠右侧后爪对机械性刺激缩足反应的阈值（PWT）;射频热凝后2周,采用Western-blotting方法测定DRG细胞Nav1．8蛋白和苏氨酸磷酸化Nav1．8蛋白表达,并采用透射电镜观察大鼠腓肠神经超微病理结构。结果 与C组比较,射频热凝前D组和R组PWT降低（P＜0．01）。射频热凝后1～2周,R组较D组PWT升高,但仍较C组降低（P＜0．05）。C组髓鞘排列均匀,轴突内可见形态正常的线粒体;D组脱髓鞘明显,髓鞘板层排列紊乱、断裂、肿胀;R组脱髓鞘程度明显减轻,髓鞘板层局部排列紊乱、空泡形成。与C组比较,D组和R组Nav1．8蛋白表达降低（P＜0．05）,而苏氨酸磷酸化Nav1．8蛋白表达增高（P＜0．01）;R组苏氨酸磷酸化Nav1．8蛋白表达低于D组（P＜0．05）。结论 DRG细胞Nav1．8的磷酸化可能是糖尿病痛性周围神经病变大鼠痛觉过敏形成的机制之一。     

硬膜外腔注射生理盐水对剖宫产术患者腰麻效果的影响

目的探讨硬膜外腔注射生理盐水对剖宫产术患者腰麻效果的影响。方法择期行子宫下段剖宫产术患者60例,年龄24～30岁,体重59～73 kg,随机分为2组,每组30例,A组蛛网膜下腔注射规定剂量的0.75%布比卡因后硬膜外腔注射生理盐水5 ml;B组蛛网膜下腔注射0.75%布比卡因。按序贯法进行试验,设定布比卡因的起始剂量为9 mg,剂量梯度为1.5 mg,若上一例有效,则下一例递减一个剂量梯度,若无效则下一例递增一个剂量梯度,蛛网膜下腔阻滞有效的标准为注射布比卡因后20 min内阻滞上平面达T5。采用概率单位法计算ED50。结果A组布比卡因的ED50（5.8 mg）低于B组（8.1 mg）,两组比值为0.72,95%置信区间为0.27～0.98,区间范围不包括1,差异有统计学意义（P〈0.05）。结论硬膜外腔注射生理盐水可增强剖宫产术患者腰麻的效果。     

Ion channel expression by white matter glia: I. Type 2 astrocytes and oligodendrocytes

White matter is a compact structure consisting primarily of neuronal axons and glial cells. As in other parts of the nervous system, the function of glial cells in white matter is poorly understood. We have explored the electrophysiological properties of two types of glial cells found predominantly in white matter: type 2 astrocytes and oligodendrocytes. Whole-cells and single-channel patch-clamp techniques were used to study these cell types in postnatal rat optic nerve cultures prepared according to the procedures of Raff et al. (Nature, 303:390-396, 1983b). Type 2 astrocytes in culture exhibit a "neuronal" channel phenotype, expressing at least six distinct ion channel types. With whole-cell recording we observed three inward currents: a voltage-sensitive sodium current qualitatively similar to that found in neurons and both transient and sustained calcium currents. In addition, type 2 astrocytes had two components of outward current: a delayed potassium current which activated at 0 mV and an inactivating calcium-dependent potassium current which activated at -30 mV. Type 2 astrocytes in culture could be induced to fire single regenerative potentials in response to injections of depolarizing current. Single-channel recording demonstrated the presence of an outwardly rectifying chloride channel in both type 2 astrocytes and oligodendrocytes, but this channel could only be observed in excised patches. Oligodendrocytes expressed only one other current: an inwardly rectifying potassium current that is mediated by 30- and 120-pS channels. Because these channels preferentially conduct potassium from outside to inside the cell, and because they are open at the resting potential of the cell, they would be appropriate for removing potassium from the extracellular space; thus it is proposed that oligodendrocytes, besides myelinating axons, play an important role in potassium regulation in white matter. The conductances present in oligodendrocytes suggest a "modulated Boyle and Conway mechanism" of potassium accumulation.     

Enhancement of blood-brain barrier permeability to sodium fluorescein by stimulation of µ opioid receptors in mice

Summary The effects of opioids on the permeability of the blood-brain barrier (BBB) were examined in mice with sodium fluorescein as an indicator of the permeability. The brain was perfused with saline 30 min after injection of sodium fluorescein (40 mg/kg, i. v.) and examined by fluorometry. Morphine hydrochloride (0.3–10 mg/kg, s. c.) markedly increased the brain level of sodium fluorescein dose-dependently without influencing the plasma level, when administered 20 min before sodium fluorescein injection. Intracerebroventricularly (i. c. v.) injected morphine hydrochloride (0.5 and 1.0 Erg) increased the brain sodium fluorescein level. Buprenorphine (0.1 and 0.5 mg/kg, s. c.) was also effective. However, pentazocine, ethylketazocine, U-50488H and SKF-10047 had no significant influence. The i.c.v. administration of [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin (0.1 g) and [D-Ala², D-Leu⁵]enkephalin (0.5 g) but not of [D-Thr², Leu⁵]enkephalin-Thr increased the brain level of sodium fluorescein significantly. A small dose of naloxone (i. p.) significantly inhibited the effects of morphine, buprenorphine, [D-Ala², McPhe⁴, Gly(ol)⁵]enkephalin and [D-Ala³, D-Leu⁵]enkephalin. ICI-174864 co-administered i. c. v. with [D-Ala², D-Leu⁵]enkephalin was ineffective in antagonizing the effect of the latter. These findings suggest that the stimulation of µ opioid receptors results in an increase in BBB permeability to sodium fluorescein. Send offprint requests to K. Saeki     

The effect of harmaline on intestinal sodium transport and on sodium-dependentd-glucose transport in brush-border membrane vesicles from rabbit jejunum

Harmaline inhibition of sodium uptake and of sodium-dependentd-glucose transport was investigated using brush-border membrane vesicles from frozen rabbit jejunum. Under sodium-gradient conditions, initiald-glucose uptake (20 s) was inhibited by harmaline at concentrations above 0.5 mM, but at lower harmaline concentrationsd-glucose uptake was stimulated by 10–15%. When a similar potassium gradient was used, harmaline had no effect. At concentrations upt to 2 mM, harmaline did not alter the equilibrium uptake ofd-glucose ord-mannitol. After pre-equlibration with sodium (25 mM),d-glucose uptake was inhibited at harmaline concentrations ranging from 0.1 to 2 mM. Sodium (10 mM) uptake was also inhibited by harmaline. Increasing the sodium concentration reduced the inhibitory effect of harmaline on tracer sodium uptake as well as on sodium-dependentd-glucose uptake. Similar to phlorizin, harmaline (1 mM) was able to prevent glucose-induced sodium influx across the brush-border membrane.Sodium uptake into brush-border membrane vesicles seems to be inhibited at lower harmaline concentrations than sodium-dependentd-glucose uptake. At high (2 mM) inhibitor concentrations, however, sodium-dependent glucose uptake is more strongly inhibited than sodium uptake. These results suggest that harmaline inhibits both sodium and sodium-dependent transport across intestinal brush-border membranes by interacting with specific sodium-binding sites.     

Control of feeding during saline consumption and fluid deprivation in hamsters

Cellular dehydration induced by water deprivation or hypertonic saline injection reduces feeding in a variety of species. Normal feeding in rats is maintained during isotonic saline consumption by increasing the intake of saline compared to the usual intake of water. Hamsters do not show the spontaneous preference for isotonic saline noted in rats, even after adrenalectomy. In the present investigation, feeding by hamsters was depressed during both isotonic and hypertonic saline consumption compared to the usual feeding with water. Saline intakes did not exceed water intakes under similar conditions. When fluid intakes were elevated by prior fluid deprivation, feeding rates increased at all concentrations of saline after a delay proportional to the osmolality of the solution. Positive 24-hr sodium balances were always associated with saline consumption. Water and hypertonic saline injections reduced feeding, and the fluid loads were excreted very slowly. When hamsters were fluid deprived prior to injections, saline totally suppressed feeding, while water increased feeding compared to sham injected controls. It is concluded that cellular dehydration produces a reduction of feeding in hamsters drinking isotonic or hypertonic saline. Reduced feeding with isotonic saline consumption results from the failure of hamsters to increase their ad lib intake of that solution. The prolonged retention of both sodium and fluid after saline consumption or injection suggests that further saline intake may be inhibited by an expansion of the extracellular space.