hCG/ATP-induced Leydig cell calcium channel reaction at different extracellular calcium ion concentration

Objective: To study the calcium channel reaction of human Leydig cells induced by hCG/ATP at different extracellular calcium ion concentrations. Methods: The Leydig cell calcium ion concentration was examined with laser confocal microscope, when the cells were stimulated with hCG/ATP at different extracellular calcium contrations. Results: With calcium-containing extracellular fluid, the Leydig cells were sensitive to hCG stimulation and when the extracellular fluid was calcium-free, the Leydig cells did not respond to the stimulation. However, the Leydig cells did respond to ATP stimulation no matter the extracellular fluid contained calcium or not. Conclusion: In human Leydig cells, there are calcium channels sensitive to hCG and ATP. The extracellular calcium ion concentration plays an important role in the regulation of Leydig cell metabolism by hCG/ATP.     

Modulation of vertebrate neuronal calcium channels by transmitters

A large number of neurotransmitters have now been shown to reduce the amplitude and slow the activation kinetics of whole cell HVA I_Ca in a great diversity of neurons. These transmitters include l-glutamate (AMPA/kainate, metabotropic and NMDA receptors), G AB A (via GABA_B receptors, NA (via α₂ receptors), 5-HT, N A (via α₂ receptors), DA and several peptides. Both whole-cell and single-channel studies have demonstrated that the N-channel is the most common channel type to be blocked by transmitters, although an inhibition of the L-type channel has also occasionally been reported. The suppression of the N-type Ca current was commonly shown to be voltage-dependent, with a relief at large positive voltages. Strong evidence has been put forward showing that the transmitter action is mediated by a G-protein, with GDP-β-S blocking transmitter action, and GTP-γ-S directly inhibiting the Ca channel. Moreover, pertussis toxin blocked the transmitter action in most neurons, and following such block, injection of the G-protein G₀ restored transmitter action. A direct link between the G-protein and the Ca channel has been widely theorized to mediate the action of transmitters on certain neurons. There is also some evidence that certain transmitters in specific neurons mediate calcium channel inhibition through a 2nd messenger, perhaps protein kinase C.Transmitters have also been found, although uncommonly, to inhibit HVA L-type and LVA T-type channels. In addition, an enhancement of both HVA and LVA, Ca currents by transmitters has been demonstrated, and substantial evidence exists for mediation of this action by cAMP.     

Cobalt-dependent potentiation of net inward current density in Helix aspersa neurons.

A low concentration of transition metal ions Co2+ and Ni2+ increases the inward current density in neurons from the land snail Helix aspersa. The currents were measured using a single electrode voltage-clamp/internal perfusion method under conditions in which the external Na+ was replaced by Tris+, the predominant external current carrying cation was Ca2+, and the internal perfusate contained 120 mM Cs+/0 K+; 30 mM tetraethylammonium (TEA) was added externally to block K+ current. In the presence of Co2+ (3 mM) or Ni2+ (0.5 mM) inward Ca2+ currents were stimulated normally by voltage-dependent activation of Ca2+ channels. There was a 5-10% decrease in the rate of rise of the inward current. The principal effect of Co2+ and Ni2+ in increasing the current density seems to be a decrease in the rate at which the inward currents decline during a depolarizing voltage pulse. The results may be due to a decrease in a voltage-dependent or Ca(2+)-dependent outward current and/or an inhibition of Ca2+ channel inactivation. Outward current under these conditions (zero internal K+) was significant and most likely due to Cs+ efflux through the voltage-activated or Ca(2+)-activated nonspecific cation channels. Co2+ is an extremely effective blocker of this outward current. These results are not an artifact of internal perfusion or the special ionic conditions. Intracellular recording of unperfused neurons in normal Helix Ringer's solution showed that the Ca(2+)-dependent action potential duration was increased significantly by low concentrations of Co2+. This result is consistant with the Co(2+)-dependent increase in inward (depolarizing) current seen in voltage-clamp experiments.     

Inward rectifying potassium channels in human malignant glioma cells

Human glioma cells obtained from established cell lines (Tp-276MG, Tp-301MG, Tp-378MG, Tp-483MG and U-251MG) were analyzed for the presence of ion channels with the tight-seal voltage clamp technique. The current-voltage relation revealed a marked inward rectification at hyperpolarizing voltages, due to the presence of inward rectifying K-channels in cells from all studied cell lines. These channels were conducting when the membrane potential was more negative than the K-equilibrium potential. The slope conductance for the inward K-currents (g_Ki) was affected both by [K⁺]_i and [K⁺]₀. g_Ki was proportional to [K⁺]₀ raised to 0.35 or 0.50, of which the larger value was measured in the presence of low [K⁺]_i (25mM). The rectification was not significantly different in cells perfused with Mg-free EDTA-buffered internal solution. Tl⁺ was 3.5 times more permaant than K⁺. g_ki was blocked by Cs⁺ (1 mM) in a voltage-dependent way (more effective in the hyperpolarized membrane), and by Na⁺ (154 mM) depending on voltage and time. From measurements of unitary current events in membrane patches (outside out or cell attached) the conductance of the single inward rectifying channel was estimated to be 27 ± 7 pS. This type of ion channel may be important for K-uptake by glial cells and hence for the K-homeostasis in the brain.     

甲基黄酮醇胺盐酸盐对异丙肾上腺素正性频率作用的影响

本文比较了甲基黄酮醇胺盐酸盐(MFOA)、普萘洛尔(Pro)、维拉帕米(Ver)对异丙肾上腺素(Iso)所致兔离体右心房正性频率作用的影响。Pro使Iso累积浓度反应曲线平行右移,不抑制最大反应,属于典型的竞争性抑制剂,其pA2=8.43;MFOA和Ver使Iso量效曲线向下右移,抑制最大反应,为非竞争性拮抗。MFOA(2×10~(-5)M)和Ver(2×10~(-7)M)分别使最大反应下降19.28％和48.57％,其pD'2值分别为4.07±0.14、6.68±0.15。结果表明MFOA的作用不同于Pro,和Ver相似。     

Phosphorylation of brain (Na+,K+)-ATPase alpha catalytic subunits in normal and epileptic cerebral cortex: I. The audiogenic mice and the cat with a freeze lesion.

Partially purified (Na+,K+)-ATPase (E.C. 3.6.1.3.) was investigated in the epileptic cortex of audiogenic DBA/2 mice and in the primary and secondary foci of cats with acute or chronic freeze lesions. No differences in specific activities measured at 3 mM K+ were observed between epileptic and control cortex, except an increase of enzymic activities in the primary focus of acutely lesioned cats. The (Na+,K+)-ATPase catalytic subunits were resolved by SDS-gel electrophoresis and their phosphorylation levels were measured in presence of K+ ions and phenytoin. K+ was more effective in inducing maximal dephosphorylation of (Na+,K+)-ATPase in C57/BL, with identical affinity in the two strains. Phenytoin decreased the net phosphorylation level of (Na+,K+)-ATPase by about 50% in C57/BL mice, but only by 20% in DBA/2 mice. Both K+ and phenytoin dephosphorylating influences were decreased in primary and secondary foci of acutely lesioned cats. Those changes were limited to the alpha(-) subunit. In chronic cats, the dephosphorylating step of the (Na+,K+)-ATPase catalytic subunit recovered a normal affinity to K+, but its sensitivity to phenytoin remained decreased. Those differences in K+ and phenytoin influences on brain (Na+,K+)-ATPases between control and epileptic cortex might be responsible for the ictal transformation and seizure spread. In cats, the alteration of the alpha(-) isoform could mainly affect the glial cells.     

以杯[4]芳烃衍生物为载体的钾离子选择电极的研究

目的：研制新的以杯[4]芳烃衍生物为载体的PVC膜钾离子选择电极。方法：以3种杯[4]芳烃衍生物为载体，癸二酸二辛酯或邻苯二甲酸二辛酯为增塑剂，四（4－氯）苯硼钾为离子定域体制得了PVC膜钾离子选择电极，测试了该类电极对钾离子的响应性能和对7种阳离子的选择性系数。结果：以5，11，17，23－四叔丁基－25，26，27，28－四[2-(乙氧基羰基）苄氧基]杯[4]芳烃为载体所制得的电极（电极Ⅰ）对钾离子有良好的能斯特响应，该电极的选择性系数优于电极Ⅱ和Ⅲ。分别用电极Ⅰ，Ⅱ，Ⅲ对青霉素V钾中的钾含量进行了测定，其结果均与原子吸收法基本一致。结论：所制得的上述电极是一类新的钾离子选择电极，有实用价值。     

大豆总皂甙对培养心肌细胞自发性搏动与动作电位的影响

培养Wistar大鼠乳鼠的心室肌细胞,向培养基中分别加入浓度为1.56μg/ml至50μg/ml的大豆皂甙,可使心肌细胞群落的自发性搏动呈剂量依赖性抑制。洗脱大豆皂甙或向培养基中再加入10μg/ml肾上腺素均能使自发性搏动恢复。向培养基中加入大豆皂甙5μg/ml使心肌细胞动作电位的波幅、波宽、超射、最大舒张电位、阈电位、最大除极速度等各电参数立即减小。Ca~(2+)80μg/ml能使动作电位的抑制逆转。上述结果表明大豆皂甙对培养的鼠心肌细胞具有钙通道阻滞用。     

Voltage-Gated calcium channels and nonvoltage-gated calcium uptake pathways in the rat incisor odontoblast plasma membrane

Odontoblasts participate actively in the transport and accumulation of Ca²⁺ ions to the mineralization front during dentinogenesis. These cells are known to carry membrane-bound ATP-driven pumps and Na⁺/Ca²⁺ antiports for Ca²⁺ extrusion, but little is known about Ca²⁺ influx mechanisms into these cells. It has been shown that the administration of Ca²⁺ channel blockers in vivo strongly impairs Ca²⁺ uptake in the mineral phase during dentinogenesis in the rat; the present in vitro study is aimed at further elucidating odontoblast Ca²⁺ uptake mechanisms. Dissected rat incisor odontoblasts exhibited a pronounced fluorescence when incubated with a fluorescently-labeled (STBodipy) dihydropyridine, which is specific for voltage-gated Ca²⁺ channels of the L-type, and this binding was competitively abolished by nifedipine. As assayed by fluorescence spectrometry, odontoblast Ca²⁺ uptake was enhanced by the agonistic dihydropyridine BAYK-8644 (5 μM) as well as by plasma membrane depolarization in a high K⁺ (120 mM) medium. The Ca²⁺ uptake after depolarization was impaired by nifedipine (5 μM). When treated with the Ca²⁺-ATPase inhibitor cyclopiazonic acid (CPA; 10 μM), a nonvoltage-gated uptake of ⁴⁵Ca²⁺ was identified. This uptake was not influenced by nifedipine (20 μM) but was impaired by lanthanum ions (200 μM). A nonvoltage-gated uptake of Mn²⁺ into CPA-treated cells could be traced using the fura-2 quenching technique. This CPA-induced Ca²⁺ flux was not caused by an alteration of the plasma membrane potential, as assayed with di-8-ANEPPS. The results demonstrate that Ca²⁺ flux into dentinogenically active odontoblasts occurs through voltage-gated Ca²⁺ channels of the L-type and by nonvoltage-gated, agonist-sensitive Ca²⁺ uptake pathways. Received: 6 November 1995 / Accepted: 21 February 1996