大鼠背根神经节神经元H+-门控离子通道电流分型及其基因型组成

目的根据大鼠背根神经节（DRG）神经元所记录的天然H^＋-门控离子通道电流特征将其进行分型，并探讨各型天然H^＋-门控离子通道与其基因型组成的酸敏感离子通道（ASICs）亚基间的相关性。方法采用全细胞膜片钳技术记录急性分离的大鼠DRG神经元H^＋-门控离子通道电流，结合单细胞免疫组化方法检测其基因型组成的ASICs亚基。结果依据H^＋-门控离子通道电流的激活及失活动力学、电流形状特点、细胞直径大小、pH依赖性等及其它参数可将H^＋-门控离子通道电流分为T-型、S．型、B-型和O-型。测定了四种类型H^＋-门控离子通道电流的激活（10%-90％21升时间）与细胞直径大小的相关性，其中T-型、B-型和O-型三种类型的激活动力学与细胞直径有关（r=0．69，P〈0．01），而S-型电流与细胞直径无关（r=0．12，P〉0．05）。对S-型电流（pH5．0）的浓度一效应关系进行了分析，其阈值在pH6．0左右，最大浓度〉2．0；在pH4．5-2．5之间出现-外向电流，浓度-效应曲线呈钟形。提供了Hi门控离子通道电流表型与其基因型的关系：T-型为ASIC1，ASIC2a，ASIC3；S．型为ASIC2a，ASIC4；B-型为ASIC1，ASIC3；O-型为ASIC1．ASIC3和ASIC4。结论大鼠DRG神经元天然H^＋-门控离子通道随着其亚基组构的改变．其电流特征也发生改变，推测系通道内向移动离子的选择性发生改变所致：其中T-型、B-型和O-型受体的神经元分布与其胞体直径相关。     

大鼠背根神经节神经元S-型与O-型H+-门控离子通道外向电流研究

目的 在前期工作的基础上,从药理学敏感性的角度出发,初步探讨S-型与O-型H+-门控离子通道外向电流的离子成分及其药理学特性.方法 采用全细胞膜片钳技术记录急性分离的大鼠背根神经节神经元H+-门控离子通道电流,测定S-型与O-型离子通道外向电流的药理学特性,分析其成分组成.结果 高浓度的胞外K+、CsC1、BaCl2、4-氨基吡啶(4-AP)、四乙基溴化铵(TEABr)、CdCl2、阿米洛利等抑制S-型与O-型H+-门控离子通道外向电流,而Ca2+络合剂EGTA和高浓度的胞外Ca2+则增强该外向电流;胞外Na+浓度的变化对该外向电流无明显影响.结论 S-型和O-型H+-门控离子通道电流的外向电流离子成分可能为钙依赖性钾电流.     

Wnt/β-连环蛋白信号通路参与调节糖皮质激素诱导的阿尔茨海默病样病变

目的 探讨Wnt/β-连环蛋白(catenin)信号通路在糖皮质激素(glucocorticoids,GC)诱导的阿尔茨海默病样病变中的信号调节机制.方法 地塞米松(dexamethasone,DEX)分别处理转染人tau441的人胚肾293细胞(HEK293/tau)和野生型的人胚肾293细胞(HEK293/wt),采用细胞计数试剂盒( CCK-8)法检测DEX对细胞活力的影响,Western blot研究两组细胞tau蛋白磷酸化(p-T205,Tau-1)、β-catenin、p-β-catenin、B细胞淋巴瘤/白血病-2蛋白(Bcl-2)及其上游激酶糖原合成激酶-3β(GSK-3β)、ps9-GSK-3β水平的变化,并加用GSK-3β的抑制剂氯化锂(LiCI),观察其对相关蛋白相应的逆转作用.结果 CCK-8细胞活力检测结果显示,1μmol/L DEX处理细胞48h,HEK293/wt组细胞活力(存活率)下降到95.5％±3.2％,HEK293/tau组下降到77.8％±4.4％,两者差异有统计学意义(t =6.60,P＜0.05);Western blot结果显示,1μmoL/L DEX处理两组细胞48 h,使得HEK293/tau细胞ps9-GSK3β、Tau -I、β-catenin、Bcl-2水平分别下降到对照组的47.8％±10.4％、53.9％±11.7％、50.9％±7.6％、48.4％±6.5％,差异均有统计学意义(t=7.01、3.86、7.09、7.30,均P＜0.05),而p-T205、p-β-catenin相对磷酸化水平分别增加到对照组的180.5％±22.2％、201.3％±27.6％,差异均有统计学意义(t=5.51、5.27,均P＜0.05);LiCI可以相应逆转上述改变.结论 在人tau存在的前提下,GC通过抑制Wnt/β-catenin信号转导通路,促进了HEK293/tau细胞的阿尔茨海默病样病变.     

拉莫三嗪对酸敏感离子通道1a的调控作用

目的探讨拉莫三嗪(lamotrigine, LTG)对酸敏感离子通道1a(acid-sensing ion channel 1a,ASIC1a)的调控作用。方法通过全细胞记录膜片钳技术研究LTG对CHO细胞转染酸敏感离子通道(acid-sensing ion channels,ASICs)不同亚型,尤其是酸敏感离子通道1a(acid-sensing ion channel 1a,ASIC1a)的调控作用及其调控方式;并通过免疫印迹定量检测LTG对ASIC1a蛋白表达的影响。结果在转染了不同的ASICs亚单位的CHO细胞系中,LTG对ASIC1a同聚体通道产生的内向电流与另外三种通道相比抑制作用显著增加(P0.05)。这种抑制效应与胞外氢离子浓度相关呈剂量依赖性,pH为6.0时,抑制率为40%左右,pH为6.8时抑制率为20%左右;并且必须与酸共给的情况下才能对ASIC1a发挥抑制效应。四组不同浓度LTG直接作用原代培养的神经元24 h后ASIC1a的蛋白表达无统计学差异(P0.05)。结论 LTG对ASIC1a同聚体通道产生的内向电流具有直接抑制作用,这可能是其治疗癫痫发作的作用机制之一。     

正常大鼠脑动脉平滑肌细胞电压依赖性钙通道电流特征

目的 研究正常大鼠脑动脉平滑肌细胞电压依赖性钙通道(VDCCs)电流的电生理和药理学特征,为相关的生理或疾病研究提供理论依据.方法 酶促消化法急性分离大鼠脑动脉平滑肌细胞,运用膜片钳电流钳技术研究其静息电位,膜片钳电压钳技术研究其电压依赖性钙通道电流以及二价阳离子载荷离子浓度和Nifedipine对其的影响.结果 静息电位为(50.42±0.26) mV,阶跃电压10 mV和斜坡电压(9.80±0.92) mV时最大VDCCs电流密度分别为(-5.22 ±0.51)pA/pF和(-4.89 ±0.65)pA/pF(10 mmol/L BaCl2).VDCCs峰电流完全由高电压激活(HVA-VDCCs)电流构成(P=0.17),无低电压激活(LVA)-VDCCs电流.VDCCs电流密度与细胞外液Ba2+浓度正相关(P＜0.05),Nifedipine对VDCCs电流的最大抑制作用为(86.13±0.76)％,IC50为6.02 nmol/L.结论 本研究证实脑动脉平滑肌细胞的VDCCs电流来源于HVA-VDCCs,以及脑动脉平滑肌细胞存在Nifedipine不敏感电流(NICCs),NICCs所依赖的离子通道以及在脑血管张力和脑血流自身调节中的作用需要进一步的研究.     

酸敏感离子通道在PC12细胞中的表达

目的：检测酸敏感离子通道（ASICs）在PC12细胞中的表达情况。方法：采用RT-PCR、Westernblot以及单细胞膜片钳记录方法检测ASICs在培养的PC12细胞中的表达情况。结果：PC12细胞中有ASICs蛋白的表达,且ASICs的6个亚基：ASIC1a,ASIC1b,ASIC2a,ASIC2b,ASIC3,ASIC4均有表达,给予酸诱导能产生电流。结论：PC12细胞上存在ASICs电流,且能被ASICs阻断剂阿米洛利所阻断,这为研究ASICs在神经退行性疾病中的作用提供了较为理想的细胞模型。     

酸敏感离子通道1a在小鼠小脑浦肯野细胞的表达

目的 探讨小鼠小脑浦肯野细胞酸敏感离子通道1a(ASIC1a)的表达及意义.方法 选用出生后第0,7,14,21,30天和2个月的SPF级C57BL/6小鼠,乙醚麻醉后取小脑组织制成切片,通过免疫荧光技术观察小鼠小脑浦肯野细胞ASIC1a的表达.结果 出生后第0,7,14,21,30天和2个月的小鼠小脑浦肯野细胞均存在ASIC1a的表达.结论 小鼠小脑浦肯野细胞存在ASIC1a的表达,对认识ASIC1a对小脑浦肯野细胞发育的作用有重要意义.     

拉莫三嗪对酸敏感离子通道1a的调控作用北大核心CSCD

目的探讨拉莫三嗪(lamotrigine, LTG)对酸敏感离子通道1a(acid-sensing ion channel 1a,ASIC1a)的调控作用。方法通过全细胞记录膜片钳技术研究LTG对CHO细胞转染酸敏感离子通道(acid-sensing ion channels,ASICs)不同亚型,尤其是酸敏感离子通道1a(acid-sensing ion channel 1a,ASIC1a)的调控作用及其调控方式;并通过免疫印迹定量检测LTG对ASIC1a蛋白表达的影响。结果在转染了不同的ASICs亚单位的CHO细胞系中,LTG对ASIC1a同聚体通道产生的内向电流与另外三种通道相比抑制作用显著增加(P<0.05)。这种抑制效应与胞外氢离子浓度相关呈剂量依赖性,pH为6.0时,抑制率为40%左右,pH为6.8时抑制率为20%左右;并且必须与酸共给的情况下才能对ASIC1a发挥抑制效应。四组不同浓度LTG直接作用原代培养的神经元24 h后ASIC1a的蛋白表达无统计学差异(P>0.05)。结论 LTG对ASIC1a同聚体通道产生的内向电流具有直接抑制作用,这可能是其治疗癫痫发作的作用机制之一。     

托吡酯对酸敏感离子通道1a调控作用的研究

目的探讨抗癫痫药物托吡酯(topiramate,TPM)对酸敏感离子通道1a(acid-sensing ion channel 1a,ASIC1a)的调控作用。方法 CHO细胞转染酸敏感离子通道(acid-sensing ion channels,ASICs)不同亚型后,通过全细胞记录膜片钳技术研究TPM对ASICs各亚型调节作用,以及对ASIC1a的具体调节模式;通过Western blot定量分析TPM对ASIC1a蛋白表达的影响。结果 TPM仅对ASIC1a同聚体通道产生的内向电流具有增强效应;这种增强效应具有剂量依赖性,且与胞外p H值相关;TPM必须与酸共给的情况下才能对ASIC1a发挥增强效应;并且TMP不影响ASIC1a的蛋白表达。结论 TPM对ASIC1a同聚体通道产生的内向电流具有直接增强作用,这可能是其治疗癫痫发作的作用机制之一。     

构建M23-AQP4稳定表达的HEK293细胞应用于血清抗AQP4抗体检测的研究

目的构建M23-AQP4稳定表达HEK293细胞(HEK293-M23-AQP4)并用于抗AQP4抗体检测,以探索临床可行的抗AQP4抗体检测方法。方法用磷酸钙转染试剂将pEGFP-N1-M23-AQP4质粒转入HEK293细胞,通过G418筛选HEK293-M23-AQP4,以细胞间接免疫荧光法(CBA)检测M23-AQP4表达及分布。以HEK293-M23-AQP4为底物的CBA法检测视神经脊髓炎(NMO)6例、多发性硬化(MS)16例、其他脱髓鞘疾病(视神经炎、脊髓炎、吉兰-巴雷综合征、急性播散性脑脊髓炎)30例、非脱髓鞘性疾病患者10例血清抗AQP4抗体及其滴度,并比较4组抗体阳性率,计算抗AQP4抗体诊断NMO的敏感性,分别以非NMO的脱髓鞘疾病和非脱髓鞘疾病作对照计算抗AQP4抗体诊断NMO的特异性。将HEK293-M23-AQP4细胞于室温、4℃、-20℃保存4周,分别作为底物检测经首次检测所得抗AQP4抗体阳性标本并随机选取5例抗体阴性标本的抗AQP4抗体及滴度,比较其阳性率及滴度变化;将上述首次检测所得抗AQP4抗体阳性标本及5例抗体阴性标本反复冻融3次后分别于室温、4℃、-20℃保存1周后,检测其抗AQP4抗体及滴度,比较阳性率和滴度变化。结果 HEK293-M23-AQP4构建成功,M23-AQP4主要表达在细胞膜上。NMO患者抗AQP4抗体阳性率达83.3%(5/6),显著高于MS患者〔6.3%(1/16)〕、其他脱髓鞘疾病〔3.3%(1/30)〕和非脱髓鞘性疾病〔0.0%(0/10)〕(均P0.01);抗AQP4抗体诊断NMO的敏感性为83.3%(5/6),以非NMO的脱髓鞘疾病作对照时,其诊断NMO特异性为95.6%(44/46),以非脱髓鞘疾病作对照时,其诊断NMO特异性为100%(10/10)。HEK293-M23-AQP4于不同温度保存后所检测抗AQP4抗体阳性率和滴度与首次检测比较均无统计学意义(均P=1.0)。血清标本4℃及-20℃保存1周后所检测抗AQP4抗体阳性率和滴度与首次检测比较差异均无统计学意义(均P=1.0);室温保存1周后抗体滴度(1∶400、1∶400、1∶3200、1∶6400、1∶6400、1∶12800、1∶51200)与首次检测(1∶800、1∶1600、1∶12800、1∶25600、1∶25600、1∶51200、1∶120400)比较均显著下降(均P0.01),但阳性率差异无统计学意义(P=1.0)。结论成功构建HEK293-M23-AQP4细胞。以此细胞为底物的CBA法检测血清抗AQP4抗体对诊断NMO的敏感性和特异性较高,且对标本存储条件要求较低。     

Extracellular trypsin increases ASIC1a selectivity for monovalent versus divalent cations

Sustained proton activation of native ASIC channels in primary sensory neurons or HEK293 cells leads to a reduction in the peak amplitude of transient inward currents and the progressive development of a persistent component, which hinders titration experiments in pharmacological studies. Here we report that extracellular trypsin applied for 5 min at 10-45 microg/ml and/or a short exposure to high Ca2+ (75 mM for less than 1 min) alleviate the persistent component, improving reproducibility of acid-elicited transients. Selectivity measurements performed in current clamp mode, in essentially bi-ionic conditions, prove that these two treatments decrease hASIC1a permeability for divalent but not for monovalent cations, producing a significant change in P(Na)/P(Ca) from 8.2+/-2.1 (mean+/-S.D.) to 26.0+/-7.8 (trypsin) or 24.5+/-11.1 (high Ca2+). The slope conductance of the unit inward Ca2+ transient was also lowered from 5.7 to 2.7 pS after trypsin.     

Otilonium bromide inhibits calcium entry through L-type calcium channels in human intestinal smooth muscle

Otilonium bromide (OB) is used as an intestinal antispasmodic. The mechanism of action of OB is not completely understood. As Ca(2+) entry into intestinal smooth muscle is required to trigger contractile activity, our hypothesis was that OB blocked Ca(2+) entry through L-type Ca(2+) channels. Our aim was to determine the effects of OB on Ca(2+), Na(+) and K(+) ion channels in human jejunal circular smooth muscle cells and on L-type Ca(2+) channels expressed heterologously in HEK293 cells. Whole cell currents were recorded using standard patch clamp techniques. Otilonium bromide (0.09-9 micromol L(-1)) was used as this reproduced clinical intracellular concentrations. In human circular smooth muscle cells, OB inhibited L-type Ca(2+) current by 25% at 0.9 micromol L(-1) and 90% at 9 micromol L(-1). Otilonium bromide had no effect on Na(+) or K(+) currents. In HEK293 cells, 1 micromol L(-1) OB significantly inhibited the expressed L-type Ca(2+) channels. Truncation of the alpha(1C) subunit C and N termini did not block the inhibitory effects of OB. Otilonium bromide inhibited Ca(2+) entry through L-type Ca(2+) at concentrations similar to intestinal tissue levels. This effect may underlie the observed muscle relaxant effects of the drug.     

Molecular cloning,distribution and functional analysis of the NA(V)1.6. Voltage-gated sodium channel from human brain

We have cloned and expressed the full-length human Na(V)1.6 sodium channel cDNA. Northern analysis showed that the hNa(V)1.6 gene, like its rodent orthologues, is abundantly expressed in adult brain but not other tissues including heart and skeletal muscle. Within the adult brain, hNa(V)1.6 mRNA is widely expressed with particularly high levels in the cerebellum, occipital pole and frontal lobe. When stably expressed in human embryonic kidney cells (HEK293), the hNa(V)1.6 channel was found to be very similar in its biophysical properties to human Na(V)1.2 and Na(V)1.3 channels [Eur. J. Neurosci. 12 (2000) 4281-4289; Pflügers Arch. 441 (2001) 425-433]. Only relatively subtle differences were observed, for example, in the voltage dependence of gating. Like hNa(V)1.3 channels, hNa(V)1.6 produced sodium currents with a prominent persistent component when expressed in HEK293 cells. These persistent currents were similar to those reported for the rat Na(V)1.2 channel [Neuron 19 (1997) 443-452], although they were not dependent on over-expression of G protein betagamma subunits. These data are consistent with the proposal that Na(V)1.6 channels may generate the persistent currents observed in cerebellar Purkinje neurons [J. Neurosci. 17 (1997) 4157-4536]. However, in our hNa(V)1.6 cell line we have been unable to detect the resurgent currents that have also been described in Purkinje cells. Although Na(V)1.6 channels have been implicated in producing these resurgent currents [Neuron 19 (1997) 881-891], our data suggest that this may require modification of the Na(V)1.6 alpha subunit by additional factors found in Purkinje neurons but not in HEK293 cells.     

Distinct detergent-resistant membrane microdomains (lipid rafts) respectively harvest K(+) and water transport systems in brain astroglia

The detergent-resistant microdomains (DRM) of cell membranes scaffold different molecules and regulate cell functions by orchestrating various signaling pathways including G-proteins and tyrosine kinase. Here we report a novel role for DRM in astroglial cells. K(+)-buffering inwardly rectifying Kir4.1 channels and the water channel AQP4 are expressed in astrocytes and they may be functionally coupled to maintain ionic and osmotic homeostasis in the brain. Kir4.1 and AQP4 channel proteins were abundant in noncaveloar DRM in the brain and also in HEK293T cells when exogenously expressed. In HEK293T cells, depletion of membrane cholesterol by methyl-beta-cyclodextrin (MbetaCD) resulted in loss of Kir4.1 association with DRM and its channel activity but did not affect either the distribution or the function of AQP4. Immunolabeling showed that Kir4.1 and AQP4 were occasionally distributed in close proximity but in distinct compartments of the astroglial cell membrane. Astroglial noncaveolar DRM may therefore be made up of at least two distinct compartments, MbetaCD-sensitive and MbetaCD-resistant microdomains, which control localization and function of, respectively, Kir and AQP4 channels on the cell membrane.     

Etodolac activates and desensitizes transient receptor potential ankyrin 1

The transient receptor potential ankyrin 1 (TRPA1) channel is well known as a sensor to environmental irritant compounds, cold, and endogenous proalgesic agents. TRPA1 is expressed on sensory neurons and is involved in pain modulation. Etodolac is a cyclooxygenase (COX)‐2 inhibitor that belongs to the class of nonsteroidal anti‐inflammatory drugs (NSAIDs). A recent study indicates that etodolac inhibits allyl isothiocyanate (AITC)‐induced calcium influx in heterologous HEK293 cells and sensory neurons. To examine whether and how etodolac modulates the TRPA1 channels, we applied etodolac to TRPA1‐transfected HEK293 cells or rat dorsal root ganglion (DRG) neurons and recorded the currents using the whole‐cell patch clamp technique. We found that etodolac at higher doses could activate and then desensitize TRPA1 channels in heterologous expressing HEK293 cells as well as in DRG neurons. The etodolac‐induced currents were significantly attenuated in cysteine residues mutated human TRPA1‐transfected HEK293 cells. Interestingly, application of etodolac at drug plasma levels in clinical usage did not induce significant TRPA1 currents but reduced the subsequent AITC‐induced currents to 25% in HEK293 cells expressing TRPA1. Moreover, no modulatory effect of etodolac on TRPA1 was detected in the cysteine mutant cells. These data indicate a novel mechanism of the anti‐inflammatory and analgesic clinical effects of etodolac, which may be involved with its direct activation and the subsequent desensitization of TRPA1 through the covalent modification of cysteine residues. © 2013 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.     

Rasmussen encephalitis associated with SCN 1 A mutation

Mutations in the SCN 1 A gene, encoding the neuronal voltage-gated sodium channel alpha1 subunit, cause SMEI, GEFS+, and related epileptic syndromes. We herein report the R1575C-SCN 1 A mutation identified in a patient with Rasmussen encephalitis. R1575C were constructed in a recombinant human SCN 1 A and then heterologously expressed in HEK293 cells along with the human beta1 and beta2 sodium channel accessory subunits. Whole-cell patch-clamp recording was used to define biophysical properties. The R1575C channels exhibited increased channel availability and an increased persistent sodium current in comparison to the wild-type. These defects of electrophysiological properties can result in neuronal hyperexitability. The seizure susceptibility allele may influence the pathogenesis of Rasmussen encephalitis in this case.     

Acidic regulation of junction channels between glomus cells in the rat carotid body. Possible role of [Ca(2+)](i)

The purpose of this work was to characterize the gap junctions between cultured glomus cells of the rat carotid body and to assess the effects of acidity and accompanying changes in [Ca(2+)](i) on electric coupling. Dual voltage clamping of coupled glomus cells showed a mean macrojunctional conductance (G(j)) of 1.16 nS+/-0.6 (S.E.), range 0.15-4.86 nS. At normal pH(o) (7.43), a steady transjunctional voltage (DeltaV(j)=100.1+/-10.9 mV) showed multiple junction channel activity with a mean microconductance (g(j)) of 93.98+/-0.6 pS, range 0.3-324.5 pS. Single-channel conductances, calculated as variance/mean g(j), gave a mean value of 16.7+/-0.2 pS, range 5.13-39.38 pS. Manual measurements of single-channel activity showed a mean g(j) of 22.03+/-0.2 pS, range 1.3-160 pS. Computer analysis of the noise spectral density distribution gave a channel mean open time of 12.7+/-1.5 ms, range 6.37-23.42 ms. The number of junction channels, estimated in each experiment from G(j)/single-channel g(j), showed a range of 7 to 258 channels (mean, 107.2). Optical measurements of [Ca(2+)](i) gave a mean value of 80.2+/-4.27 nM at pH(o) of 7.43. Acidification of the medium with lactic acid (1 mM, pH 6.3) induced: 1) Variable changes in G(j) (decreases and increases); 2) A significant decrease in mean g(j) (to 80.36+/-0.34 pS) and in single-channel conductance (g(j)=12.8+/-0.2 pS in computer analyses and 17.23+/-0.2 pS when measured by hand); 3) Variable changes in open times, resulting in a similar mean (12.8+/-1.5 ms) and 4) No change in the number of junction channels. When pH(o) was lowered to 6.3 [Ca(2+)](i) did not change significantly (there were increases and decreases). However, when pH(o) was lowered to 4.4, [Ca(2+)](i) increased significantly to 157.1+/-8.1 nM. It is concluded that saline acidification to pH 6.3 depresses the conductance of junction channels and this effect may be either a direct effect on channel proteins or synergistically enhanced by increases in [Ca(2+)](i). However, there are no studies correlating changes of [Ca(2+)](i) and intercellular coupling in glomus cells. Stronger acidification (pH(o) 4.4), producing much larger changes in [Ca(2+)](i), may enhance this synergism. But, again, there are no studies correlating these effects.     

Characteristics of IA currents in adult rabbit cerebellar Purkinje cells

Classical conditioning the rabbit nictitating membrane involves changes in synaptic and intrinsic membrane properties of cerebellar Purkinje cell dendrites, and a 4-aminopyridine (4-AP)-sensitive potassium channel underlies these membrane properties. We characterized I(A) currents in adult, rabbit Purkinje cells to determine whether I(A) is the target channel involved in learning. Whole-cell recordings of Purkinje cell somas and dendrites revealed a fast activating and inactivating current with half maximal activation at -27.08 +/- 3.48 mV and -25.51 +/- 1.15 mV in somas and dendrites, respectively; half maximal inactivation at -58.91 +/- 2.34 mV and -49.90 +/- 2.58 mV; and a recovery time constant of 22.81 +/- 1.92 ms and 16.60 +/- 4.26 ms. Outside-out patch recordings from cerebellar Purkinje cell somas confirmed these 4-AP-sensitive currents with half maximal activation at -13.85 +/- 1.17 mV and half maximal inactivation at -55.07 +/- 5.54 mV. More importantly, there was an overlap of activation and incomplete inactivation at potentials from -60 to -40 mV, suggesting a "window" current that was responsible for subthreshold variations of membrane potential and might underlie conditioning-specific increases in Purkinje cell excitability. The potassium current was inhibited by 4-AP and by Heteropodatoxin, a specific blocker of Kv4.2 and Kv4.3 channels, but not by Stromatoxin, a blocker of Kv4.2 channels. Mouse monoclonal antibody labeling identified both Kv4.3 and Kv4.2 subunits in the granule cell layer but only Kv4.3 subunits in the molecular layer. This is the first demonstration of A-type currents in adult, rabbit Purkinje cells that may play a role in regulating membrane potential and firing frequency and comprise the target channel mediating conditioning-specific changes of excitability in rabbit Purkinje cell dendrites.     

Purification and mass spectrometric analysis of the delta opioid receptor

A mouse delta opioid receptor was engineered to contain a FLAG epitope at the amino-terminus and a hexahistidine tag at the carboxyl terminus to facilitate purification. Selection of transfected human embryonic kidney (HEK) 293 cells yielded a cell line that expressed the receptor with a B(max) of 10.5 pmol/mg protein. [3H]Bremazocine exhibited high affinity binding to the epitope-tagged delta opioid receptor with a K(D) of 1.4 nM. The agonists DADL, morphine, and DAMGO competitively inhibited bremazocine binding to the tagged delta receptor with K(I)'s of 0.9, 370, and 620 nM, respectively. Chronic treatment of cells expressing the epitope-tagged delta receptor with DADL resulted in downregulation of the receptor, indicating that the tagged receptor retained the capacity to mediate signal transduction. The delta receptor was solubilized from HEK 293 cell membranes with n-dodecyl-beta-d-maltoside in an active form that maintained high affinity bremazocine binding. Sequential use of Sephacryl S300 gel filtration chromatography, wheat germ agglutinin (WGA)-agarose chromatography, immobilized metal affinity chromatography, immunoaffinity chromatography, and SDS/PAGE permitted purification of the receptor. The purified delta opioid receptor was a glycoprotein that migrated on SDS/PAGE with an apparent molecular mass of 65 kDa. MALDI-TOF mass spectrometry was used to identify and characterize peptides derived from the delta opioid receptor following in-gel digestion with trypsin, and precursor-derived ms/ms confirmed the identity of peptides derived from enzymatic digestion of the delta opioid receptor.