心房肌复极的电整复性与阵发性心房颤动发生机制的实验研究

目的 研究在体犬左、右心房肌的电整复性即动作电位时程整复性(APDR),观察其与阵发性心房颤动(房颤)发生的潜在机制.方法 使用单相动作电位技术记录14只犬左、右心房复极达90%的动作电位时程(APD_(90)),并通过S_1S_2程序刺激,观察APDR变化,即每一个舒张间期与刺激后发生心房肌复极APD_(90)的关系,并观察房颤的诱发情况.结果 APD_(90)左心房为(157.4±43.5)ms明显小于右心房(170.9±37.9)ms,P<0.05.心房肌在S_1S_2递减程序刺激下,左心房与右心房具有不同斜率的APDR曲线,左心房的APDR曲线斜率1.3±0.4大于右心房0.9±0.3,P<0.05.进行心房快速起搏S_1S_2刺激时,14只犬中共诱发出18阵房颤,其中左心房刺激发作12阵,明显多于右心房6阵(P<0.05).结论 左、右心房间具有单相动作电位时程的异质性及APDR不均一的复极特性,是诱发折返、发生和维持房颤的基质之一.     

Functional coupling between heterologously expressed dopamine D(2) receptors and KCNQ channels

Activation of KCNQ potassium channels by stimulation of co-expressed dopamine D₂ receptors was studied electrophysiologically in Xenopus laevis oocytes and in mammalian cells. To address the specificity of the interaction between D₂-like receptors and KCNQ channels, combinations of KCNQ1–5 channels and D₂-like receptors (D_2L, D₃, and D₄) were investigated in Xenopus oocytes. Activation of either receptor with the selective D₂-like receptor agonist quinpirole (100 nM) stimulated all the KCNQ currents, independently of the subunit combination, indicating a common pathway of receptor-channel interaction. The KCNQ4 current was investigated in further detail and was increased by 19.9±1.6% (n=20) by D_2L receptor stimulation. The effect could be mimicked by injection of GTPS and prevented by injection of Bordetella pertussis toxin, indicating that channel stimulation was mediated via a G protein of the G_i/o subtype. Cells of the human neuroblastoma line SH-SY5Y were co-transfected transiently with KCNQ4 and D_2L receptors. Stimulation of D_2L receptors increased the KCNQ4 current (n=6) as determined in whole-cell patch-clamp recordings. The specificity of the dopaminergic activation of the KCNQ channels was confirmed by co-expression of other neuronal K⁺ channels (BK, K_V1.1, and K_V4.3) with the D_2L receptor in Xenopus oocytes. None of these K⁺ channels responded to stimulation of the D_2L receptor. In the mammalian brain, dopamine D₂ receptors and KCNQ channels co-localise postsynaptically in several brain regions, so modulation of neuronal excitability by dopamine release could in part be mediated via an effect on KCNQ channels.     

Functional role of low-voltage-activated dihydropyridine-sensitive Ca channels during the action potential in adult rat sensory neurones

Neuronal cell firing is crucial to nerve-nerve communication. The ability to produce consecutive action potentials is related to the activation of inward currents after each upstroke. If fast Na current is indeed responsible for the overshoot, it is still unclear which current drives membrane voltage to the Na threshold. In this study we present evidence that in adult rat sensory neurones a dihydropyridine-sensitive Ca channel exists in addition to the well characterized L-type, or high-threshold Ca channel. During stimulated action potential trains, L-type Ca channels open during the excitation wave, whereas activity of the other dihydropyridine-sensitive Ca channel was observed primarily between action potentials. This second Ca pathway shows remarkably long openings at negative potentials after a series of positive prepulses. The nerve action potential and the repetitive firing work as a physiological Ca channel facilitation mechanism. Therefore, we suggest that this novel Ca conductance provides inward current, between two consecutive action potentials, able to modulate the frequency of neuronal bursts. Received: 3 August 1995/Received after revision: 9 October 1995/Accepted: 10 October 1995     

Altered GABAA receptor subunit expression and pharmacology in human Angelman syndrome cortex

The neurodevelopmental disorder Angelman syndrome is most frequently caused by deletion of the maternally derived chromosome 15q11-q13 region, which includes not only the causative UBE3A gene, but also the β₃-α₅-γ₃ GABA_A receptor subunit gene cluster. GABAergic dysfunction has been hypothesized to contribute to the occurrence of epilepsy and cognitive and behavioral impairments in this condition. In the present study, analysis of GABA_A receptor subunit expression and pharmacology was performed in cerebral cortex from four subjects with Angelman syndrome and compared to that from control tissue. The membrane fraction of frozen postmortem neocortical tissue was isolated and subjected to quantitative Western blot analysis. The ratios of β₃/β₂ and α₅/α₁ subunit protein expression in Angelman syndrome cortex were significantly decreased when compared with controls. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage-clamp analysis of GABA_A receptor currents was then performed. Studies of GABA_A receptor pharmacology in Angelman syndrome cortex revealed increased current enhancement by the α₁-selective benzodiazepine-site agonist zolpidem and by the barbiturate phenobarbital, while sensitivity to current inhibition by zinc was decreased. GABA_A receptor affinity and modulation by neurosteroids were unchanged. This shift in GABA_A receptor subunit expression and pharmacology in Angelman syndrome is consistent with impaired extrasynaptic but intact to augmented synaptic cortical GABAergic inhibition, which could contribute to the epileptic, behavioral, and cognitive phenotypes of the disorder.     

Long-latency auditory evoked potentials with verbal and nonverbal stimuli

IntroductionLong-latency auditory evoked potentials represent the cortical activity related to attention, memory, and auditory discrimination skills. Acoustic signal processing occurs differently between verbal and nonverbal stimuli, influencing the latency and amplitude patterns.ObjectiveTo describe the latencies of the cortical potentials P1, N1, P2, N2, and P3, as well as P3 amplitude, with different speech stimuli and tone bursts, and to classify them in the presence and absence of these data.MethodsA total of 30 subjects with normal hearing were assessed, aged 18–32 years old, matched by gender. Nonverbal stimuli were used (tone burst; 1000 Hz – frequent and 4000 Hz – rare); and verbal (/ba/ – frequent; /ga/, /da/, and /di/ – rare).ResultsConsidering the component N2 for tone burst, the lowest latency found was 217.45 ms for the BA/DI stimulus; the highest latency found was 256.5 ms. For the P3 component, the shortest latency with tone burst stimuli was 298.7 with BA/GA stimuli, the highest, was 340 ms. For the P3 amplitude, there was no statistically significant difference among the different stimuli. For latencies of components P1, N1, P2, N2, P3, there were no statistical differences among them, regardless of the stimuli used.ConclusionThere was a difference in the latency of potentials N2 and P3 among the stimuli employed but no difference was observed for the P3 amplitude.     

ATP敏感性钾通道P266T突变对离子通道特性的影响

目的： 通过通道蛋白特定位点(P266T)突变,观察对ATP敏感性钾通道电生理特性的影响。 方法: 将Kir6.2及其突变子P266T的cDNA导入人胚肾细胞，表达ATP敏感性钾通道，用膜片钳方法研究K_ATP电生理特性。 结果: K_ATP(P266T)开放能力是野生型的2倍; K_ATP(P266T)密度仅是野生型20%; K_ATP(P266T)对ATP敏感性降低;对pH敏感性增高。 结论: K_ATP特定位点(P266T)突变可改变K_ATP电生理特性。     

川芎嗪对休克血浆所致乳头肌电生理效应的影响

目的探讨川芎嗪（Lig）对休克血浆（SP）所致豚鼠心室乳头肌电生理特性改变的干预作用。方法利用常规玻璃微电极细胞内记录技术，观察SP对豚鼠心室乳头肌动作电位的影响及不同剂量Lig的干预作用。结果（1）用含有SP的灌流液灌流标本时，豚鼠心室乳头肌细胞动作电位的幅值（APA）、超射值（OS）均显著升高（P〈0．05），复极50％、90％时间（APD50、APD90）及动作电位时程（APD）均明显延长（P〈0．05）；（2）Lig可剂量依赖性地降低SP引起的APA、OS升高，延长APD50、APD90及APD，此种干预作用以5．12mmol／L Lig最为明显。结论SP可导致正常豚鼠心室乳头肌电生理特性的改变，而Lig可剂量依赖性地干预此种效应。     

Erythropoietin and its antagonist regulate hypoxic fictive breathing in newborn mice

Clinical use of erythropoietin in adult and newborn patients has revealed its involvement in neuroprotection, neurogenesis, and angiogenesis. More recently, we showed in adult mouse, that brain erythropoietin interacts with the major brainstem centers associated with respiration to enhance the ventilatory response to acute and chronic conditions of physiological hypoxia (e.g., as occurring at high altitude). However, whether brain erythropoietin is involved in breathing regulation in newborns remains unknown. In this study, en bloc brainstem-spinal cord preparations were obtained from mice at postnatal day 4. After various periods (30, 60, or 90 min) of incubation with 0, 25, or 250 U of erythropoietin, preparations were superfused with artificial cerebrospinal fluid bubbled with normoxic or hypoxic gas mixtures. The electrophysiological fictive breathing produced by axons at the C4 ventral root was next recorded. Our results show that erythropoietin attenuates the hypoxia-mediated decrease of the central respiratory activity and improves post-hypoxic recovery. Additional analysis revealed that the soluble erythropoietin receptor (the endogenous erythropoietin antagonist) dramatically decreases neural hypoxic respiratory activity, confirming the specific erythropoietin effect on respiratory drive. These results imply that erythropoietin exerts main modulation and maintenance of respiratory motor output during hypoxic and post-hypoxic challenges in 4-days old mice.     

融合影像导航和电生理监测显微手术治疗运动区肿瘤

目的:探讨血氧水平依赖性功能磁共振成像(BOLD-fMRI)及弥散张量-纤维示踪成像(DTI-FT)融合神经导航,结合术中电生理监测在手术治疗颅内运动区肿瘤的临床应用价值.方法:对15例运动区肿瘤患者,术前行导航薄层扫描、BOLD-fMRI及DTI-FT,并在导航仪上进行三者影像融合,了解肿瘤、运动区及锥体束相对关系.术中在导航引导下定位肿瘤、运动区及锥体束,结合术中电生理实时定位肿瘤周围脑功能边界,在显微镜内导航引导下切除肿瘤.结果:导航精确成像,BOLD-fMRI与术中电生理提示基本一致,DTI-FT指导切除肿瘤中保护纤维束.15例肿瘤中全切除12例,次全切除2例,大部切除1 例.术后随访3 ～10个月,术后4 例出现一过性肌力减退加重,随访末期其肢体肌力均基本恢复至术前,其余11例肌力水平与术前比较均有好转或不变.结论:MRI、BOLD-fMRI及DTI-FT融合导航,结合术中电生理监测,可实现镜内导航下最大程度切除运动区肿瘤的同时尽量避免运动区和锥体束的损伤,有效保护神经功能,提高病人术后的生活质量.