17β-Estradiol depolarization of hypothalamic neurons is mediated by cyclic AMP

The process by which 17β-estradiol rapidly modulates the excitability of neurons in the ventromedial hypothalamus, a facilitation center of female sexual behavior and satiety center of feeding behavior, through mediation by cyclic nucleotides, was investigated by intracellular recording from the guinea pig brain slice preparations. Two types of short-term responses were produced by depolarization with decreased K⁺ conductance and hyperpolarization with increased K⁺ conductance. These two responses were enhanced by the phosphodiesterase inhibitor, isobutylmethylxanthine. However, the specific adenylate cyclase activator, forskolin, enhanced only the depolarization. The analogue of cyclic adenosine 3′,5′-monophosphate (cAMP), 8-bromo-cAMP, induced only depolarization, the ionic mechanism of which was similar to that of 17β-estradiol. In addition, the possibility of non-specific effects of cyclic nucleotides was precluded by an experiment using an analogue of cyclic guanosine 3′,5′-monophosphate (cGMP), 8-bromo-cGMP, which hyperpolarized neurons. Thus, the present study strongly suggests that the production of depolarizing responses of neurons in the hypothalamus produced by estradiol is specifically mediated through cAMP.     

咪唑安定对大鼠海马锥体细胞延迟整流K+通道的作用

目的探讨咪唑安定对大鼠海马锥体细胞上延迟整流K+通道(IK)的作用,及在其麻醉作用中的机制.方法急性分离大鼠海马锥体细胞,采用全细胞模式测定延迟外向整流K+电流,钳制电压由-50mV去极化至+30mV,加用不同浓度咪唑安定后测量电流的幅度变化.结果咪唑安定呈剂量性相关抑制延迟外向整流K+通道,EG50(8.31±2.78)×10-8 mol/L,Hill系数0.90±0.16.结论咪唑安定对延迟外向整流K+通道有抑制作用.     

Blockade of bepridil on IA and IK in acutely isolated hippocampal CA1 neurons

The effects of bepridil, an antianginal agent with antiarrhythmic action, on voltage-dependent K⁺ currents in the CA1 pyramidal neurons acutely isolated from rat hippocampus were studied by means of whole-cell patch clamp techniques. Current recordings were made in the presence of TTX to block Na⁺ current. Depolarizing test pulses activated two components of outward K⁺ currents: a rapidly activating and inactivating component, I_A; and a delayed component, I_K. Results showed that bepridil reduced the amplitude of I_A and I_K, and exerted its inhibitory action in time- and dose-dependent manner. Half-blocking concentrations (IC₅₀) of bepridil on I_A and I_K were 17.8 μM and 1.7 μM, respectively. 10 μM bepridil suppressed I_A and I_K by 46.7% and 77.1% at +30 mV of depolarization, respectively. When I_K was activated nearly uncontaminated with I_A by holding at −50 mV, 10 μM bepridil inhibited I_K by 71.6% at +30 mV of depolarization; 10 μM bepridil positively shifted the voltage-dependent of activation curves of I_A and I_K 12.1 mV and 28.7 mV, respectively. These results suggested that blockade on K⁺ currents by bepridil is preferential for I_K, and contributes to the protection brain against ischemic damage.     

Electrocardiographic monitoring in children with chronic renal failure

Continuous electrocardiographic (ECG) monitoring was performed over 24 h in 44 children at various stages of chronic renal failure in order to determine the incidence and nature of cardiac dysrhythmias. In addition the ECG was followed during haemodialysis sessions and during dialysate exchanges in continuous ambulatory peritoneal dialysis (CAPD) patients. In contrast to adult patients on haemodialysis life-threatening dysrhythmias were not observed. The proportion of children with premature ventricular complexes (41%) was at the upper limit of that in healthy children. A relatively high heart rate was found in children on CAPD, which varied during the exchange procedure. In 57% of all patients a transient marked prolongation of the QT interval up to 40% greater than normal was observed without obvious changes in the serum electrolyte levels. Continuous ECG monitoring is a useful tool for detecting alterations of cardiac rhythm and conduction in at-risk children with renal failure.     

Glutamate and kainate increase intracellular sodium activity in leech neuropile glial cells

Na+-selective, double-barrelled microelectrodes were used to measure intracellular Na+ activity (aiNa) and membrane potential (Em) in neuropile glial cells of isolated segmental ganglia in the leech Hirudo medicinalis. Bath application of glutamate (10(-3) M) resulted in membrane depolarizations of about 5 mV and a concomitant increase of aiNa by between 2 and 10 mM. Kainate (10(-4) M) elicited depolarizations of up to 40 mV amplitude followed by a prominent after hyperpolarization. During kainate, aiNa increased by 7 to 25 mM. In contrast to glutamate, an initial decrease of aiNa was detected during the action of kainate. N-methyl-D-aspartate (NMDA, 10(-5)-10(-3) M) had no effect of Em and aiNa. The results indicate that leech glial cells have a kainate-preferring non-NMDA glutamate receptor.     

用于分子生物学中DNA快速提取技术的研究

本文建立了应用碘化钾快速提取DNA的方法，提取55份外周血及14份骨髓标本，用紫外分光光度计检测其纯度和浓度，并用于一系列分子试验加以验证获得满意效果。     

Anoxia reduces depolarization induced calcium uptake in the rat hippocampal slice

Veratridine-induced depolarization caused a large increase in Ca uptake in the rat hippocampal slice (30.2 vs. 9.0 nM/mg dry weight). This uptake was reduced to 18.4 nM/mg when veratridine was combined with anoxia. When compared with veratridine exposure alone, the combination of anoxia and veratridine increased intracellular Na(460 vs. 380 μM/g), decreased intracellular K (30 vs. 40 μM/g) and decreased ATP levels (0.1 vs. 0.8 nM/mg). The changes in Na, K, and ATP should enhance net Ca uptake, yet Ca uptake was reduced. This suggests an effect of anoxia to block Ca channels. In summary anoxia attenuates depolarization-induced Ca uptake. This may represent a mechanism by which neurons are partially protected against anoxic damage which could be more severe if depolarization-induced Ca uptake was not limited.     

复方乳酸钠注射液的重铬酸钾法测定

用重铬酸钾法测定复方乳酸钠注射液中的乳酸钠，方法简便、快速，准确。回收率为１００．０％（ＲＳＤ＝０．４５％）。     

Dopamine neuron membrane physiology: Characterization of the transient outward current (IA) and demonstration of a common signal transduction pathway for IA and IK

Dopamine neurons derived from the mesencephalon of embryonic rats were maintained in primary culture, identified and studied with whole-cell patch recording techniques. These neurons demonstrated a rapidly activating and inactivating voltage-dependent outward current which required the presence of K⁺ ions. This current was termed I_A because of its transient nature. It was elicited by step depolarizations from holding potentials more negative than -50 mV and exhibited steady-state inactivation at a membrane potential more positive than -40 mV and half-maximal inactivation observed at -65 mV. This current rapidly achieved peak activation in less than 8 msec and decayed with a time constant (τ) of 58±5 msec. This current was observed in the presence of tetraethylammonium but was readily blocked by 4-aminopyridine (2-4 mM). This current was also observed to be modulated by stimulation of D₂ dopamine receptors (DA autoreceptors) located on the dopamine neurons. Thus, both DA and the D₂ receptor agonist quinpirole enhanced the peak I_A observed, while the partial D₁ receptor agonist SKF 38393 was without effect. The enhancement of I_A was confirmed to be due to the activation of D2 receptors as the effects of either DA or quinpirole were blocked by the D₂ receptor antagonists eticlopride and sulpiride, but not by the D₁ receptor antagonist SCH 23390. Since we have previously demonstrated that the I_K present: in these cells is also enhanced by D₂ receptor stimulation, we investigated the signal transduction pathways involved in coupling DA autoreceptors to both I_A and I_K. The response of both these potassium currents to DA autoreceptor stimulation was completely abolished by the preincubation of cultures with pertussis toxin, indicating the possible involvement of the G proteins G_i and G_O. In an attempt to further characterize which G protein may be involved, additional experiments were performed. The ability of DA autoreceptor stimulation to augment both currents was also blocked completely when G protein activation was prevented by the intracellular application of GDPßS (100 μM). In contrast, irreversible activation of G proteins by intracellular application of the nonhydrolyzable GTP analog GTPγS (100 μM) mimicked the effects of DA autoreceptor stimulation on both I_A and I_K. In addition, the intracellular application of a polyclonal antibody that was selective for the β-subunit of G_O completely abolished the DA autoreceptor modulation of both currents while preimmune serum was without effect. Taken together, these data demonstrate that the enhancement of I_A and I_K in response to stimulation of DA autoreceptors is dependent upon the activation of G_O and appears to involve a G_Oα subunit. © 1994 Wiley-Liss, Inc.     

Two components of Ca-dependent potassium current in identified neurones ofAplysia californica

Outward tail currents measured inAplysia neurones after termination of depolarizing voltage-clamp pulses consist of rapidly decaying voltage-dependent K currents and slow tail currents of much slower time course. The rapidly decaying voltage-dependent tail currents were blocked with aminopyridines, and measurements of the slow tail currents were made following decay of any residual rapid tail currents. The slow tail current exhibited two components of differing sensitivity to externally applied tetraethylammonium (TEA) ions. In some neurones of the abdominal ganglion (L-2, L-4), virtually all of the slow tail current was resistant to blockage by TEA, while in others (L-3, L-6) 80% or more of the slow tail current was blocked by low TEA concentrations (K _D<1 mM), the remaining slow tail current being resistant to TEA. This TEA-resistant slow tail current was identified as a K current because it reversed near the K equilibrium potential (E _K), the reversal potential was shifted by changes in the external K concentration, and it could be blocked by injection of Cs⁺. It was abolished by replacement of external Ca²⁺ by Co²⁺ or Ba²⁺, by addition of Cd²⁺, or by injection of EGTA, and thus determined to be a Ca-dependent current. Intracellular injection of TEA or external application of aminopyridine or apamine had little or no effect on the TEA-resistant slow tail current. Quinidine reduced the TEA-sensitive, but not the TEA-resistant current. Both the TEA-sensitive and the TEA-resistant components of the slow tail current exhibited similar time courses of decay. Thus, neurones ofAplysia appear to contain different proportions of two classes of Ca-dependent K channels that differ in their sensitivity to certain channel blocking agents.