Evidence for a dose-dependent effect of pulsed magnetic fields on pain processing

Functional magnetic resonance imaging (fMRI) was used to investigate the dose–response relationship (sham, 100, 200, 1000 μT) between a pulsed extremely low frequency magnetic field (ELFMF) and acute thermal pain on the dominant right hand. Forty-seven participants were recruited, and pulsed ELFMF was applied through the MRI gradient system using a novel technique. Regions of interest (ROIs) matching those of previous studies were examined for a potential dose response. Significant correlations between applied field strength and change in BOLD activity were found in the anterior cingulate and the ipsilateral insula, indicating that there might be either a dose response or a threshold effect of the ELFMF.     

Ca2+-dependent modulation of single human cardiac L-type calcium channels by the calcineurin inhibitor cyclosporine

OBJECTIVE: Activity of single L-type calcium channels (LTCC) is enhanced in human failing myocardium (Circulation 98 (1998) 969.), most likely due to impaired dephosphorylation. Protein phosphatase 2B (calcineurin) has recently been shown to be involved in heart failure pathophysiology. We now focus on the regulation of single LTCC by calcineurin that were prevented by Ca(2+)-free experimental conditions in our previous study. METHODS: Single LTCC currents were recorded in myocytes from human atrium and ventricle. Charge carriers were 70 mM Ba(2+), or a mixture of 30 mM Ca(2+) and 60 mM Ba(2+) to facilitate Ca(2+) permeation through recorded channels. The calcineurin inhibitor cyclosporine (10 microM) was used to reveal a putative role for calcineurin in regulation of LTCC. RESULTS: A mixture of Ca(2+) and Ba(2+) as charge carriers allowed for Ca(2+) permeation through recombinant human embryonic kidney cells and native (atrial and ventricular) human cardiac LTCC. With only Ba(2+) as the charge carrier, activities of both ventricular and atrial LTCC were strongly decreased by cyclosporine. In contrast, channel activity remained constant when Ca(2+) permeation was provided. In the presence of thapsigargin and (S)-BayK 8644, cyclosporine here even increased channel activity. CONCLUSIONS: We propose a dual cyclosporine effect on human cardiac LTCC. A non-specific inhibitory effect prevails with Ba(2+) permeation but can be compensated or overcome by a specific Ca(2+)-dependent stimulation with Ca(2+) permeation. More complete restoration of physiological Ca(2+) movements (e.g., Ca(2+) release from sarcoplasmic reticulum) will help to define even more precisely the involvement of calcineurin in regulation of human cardiac LTCC.     

J波与J波综合征

J波是指心电图上QRS波与ST段之间的圆顶状或驼峰状电位变化。新近临床研究表明，在早期复极综合征、Brugada综合征和特发性心室颤动等心电图中，均存在J波形态、时限和幅度的显著改变，上述与J波密切相关的一系列临床综合征统称为J波综合征。本文详尽阐述了J波的细胞电生理和离子流机制，分析了早期复极综合征、Brugada综合征、心电图下壁导联高大J波相关的心脏性猝死的临床特点及内在机制。     

犬右房不同部位Kv4.3、KchIP2、Cav1.2 mRNA的表达

目的研究犬右房不同部位短暂外向钾电流、L型钙电流亚单位mRNA的表达情况,探讨其在致房性心律失常中的意义。方法应用逆转录-聚合酶链反应半定量分析犬界嵴、梳状肌、右心耳的短暂外向钾电流α亚单位(Kv4.3)、β亚单位(KchIP2)及L型钙电流的α亚单位(Cav1.2)mRNA的表达量(以β-actin为内参照)。结果界嵴和梳状肌Kv4.3、KchIP2 mRNA高于右心耳(P<0.05或0.01);界嵴Cav1.2 mRNA高于梳状肌和右心耳(P均<0.05),而梳状肌和右心耳之间没有差异。结论Kv4.3、KchIP2、Cav1.2 mRNA在右房空间表达上的差异与其相应离子流在右房空间上的差异一致,可能是其离子流差异的分子基础。     

Enhanced activation of an amino-terminally truncated isoform of the voltage-gated proton channel HVCN1 enriched in malignant B cells

HVCN1 (Hydrogen voltage-gated channel 1) is the only mammalian voltage-gated proton channel. In human B lymphocytes, HVCN1 associates with the B-cell receptor (BCR) and is required for optimal BCR signaling and redox control. HVCN1 is expressed in malignant B cells that rely on BCR signaling, such as chronic lymphocytic leukemia (CLL) cells. However, little is known about its regulation in these cells. We found that HVCN1 was expressed in B cells as two protein isoforms. The shorter isoform (HVCN1_S) was enriched in B cells from a cohort of 76 CLL patients. When overexpressed in a B-cell lymphoma line, HVCN1_S responded more profoundly to protein kinase C-dependent phosphorylation. This more potent enhanced gating response was mediated by increased phosphorylation of the same residue responsible for enhanced gating in HVCN1_L, Thr²⁹. Furthermore, the association of HVCN1_S with the BCR was weaker, which resulted in its diminished internalization upon BCR stimulation. Finally, HVCN1_S conferred a proliferative and migratory advantage as well as enhanced BCR-dependent signaling. Overall, our data show for the first time, to our knowledge, the existence of a shorter isoform of HVCN1 with enhanced gating that is specifically enriched in malignant B cells. The properties of HVCN1_S suggest that it may contribute to the pathogenesis of BCR-dependent B-cell malignancies.The voltage-gated proton channel HVCN1 (or H_V1 or VSOP) is a small protein that conducts protons across membranes selectively (1, 2) and in a regulated manner. Previously, we described its function in B lymphocytes, where proton channels sustain B-cell receptor (BCR) signaling via regulation of reactive oxygen species production by the NADPH oxidase enzyme complex (3). In addition, we found HVCN1 to be directly associated with the BCR. Upon receptor stimulation, the BCR and HVCN1 were cointernalized to late endosomal/lysosomal organelles called “MIICs,” or MHC class II-containing compartments, where antigens bound to the BCR are digested into small peptides and loaded onto MHC class II molecules for presentation to T cells (3).HVCN1 is expressed not only by normal but also by malignant B cells, such as those in chronic lymphocytic leukemia (CLL) (3). CLL cells are characterized by their reliance on BCR signaling for survival and growth (4), so it is possible that they maintain or upregulate HVCN1 expression to sustain their growth. Other tumor cells, such as those in breast (5) and colorectal cancer (6), have been found to rely on HVCN1 for survival. In these tumor cells, proton channels prevent excessive acidification of the cytoplasm and allow increased cell migration. In malignant B cells, HVCN1 may regulate intracellular pH and at the same time sustain BCR signaling. However, its precise roles remain to be elucidated.We show here that CLL cells and other B-cell lines specifically express higher levels of a shorter isoform of HVCN1, HVCN1_S. We identified the existence of two distinct isoforms of relatively similar size when immunoblotting B-cell lysates with an HVCN1-specific antibody (3). HVCN1_S is only weakly expressed in normal B cells, and in light of its apparent upregulation in tumor cells, we set out to characterize its function. We show that HVCN1_S responds more strongly to phosphorylation by protein kinase C (PKC) and identify the phosphorylation site. We provide evidence that HVCN1_S in B cells is preferentially expressed at the plasma membrane, even upon BCR stimulation and subsequent internalization, due to a weaker association with the BCR. Finally, we show that HVCN1_S expression results in stronger BCR signaling, increased proliferation, and augmented chemokine-dependent migration. Overall, our data indicate that HVCN1_S is an alternative protein isoform that mediates stronger currents upon PKC phosphorylation, is more highly expressed at the plasma membrane, and can confer a growth advantage to malignant B cells.     

UDP‐glucose enhances outward K+ currents necessary for cell differentiation and stimulates cell migration by activating the GPR17 receptor in oligodendrocyte precursors

In the developing and mature central nervous system, NG2 expressing cells comprise a population of cycling oligodendrocyte progenitor cells (OPCs) that differentiate into mature, myelinating oligodendrocytes (OLGs). OPCs are also characterized by high motility and respond to injury by migrating into the lesioned area to support remyelination. K⁺ currents in OPCs are developmentally regulated during differentiation. However, the mechanisms regulating these currents at different stages of oligodendrocyte lineage are poorly understood. Here we show that, in cultured primary OPCs, the purinergic G‐protein coupled receptor GPR17, that has recently emerged as a key player in oligodendrogliogenesis, crucially regulates K⁺ currents. Specifically, receptor stimulation by its agonist UDP‐glucose enhances delayed rectifier K⁺ currents without affecting transient K⁺ conductances. This effect was observed in a subpopulation of OPCs and immature pre‐OLGs whereas it was absent in mature OLGs, in line with GPR17 expression, that peaks at intermediate phases of oligodendrocyte differentiation and is thereafter downregulated to allow terminal maturation. The effect of UDP‐glucose on K⁺ currents is concentration‐dependent, blocked by the GPR17 antagonists MRS2179 and cangrelor, and sensitive to the K⁺ channel blocker tetraethyl‐ammonium, which also inhibits oligodendrocyte maturation. We propose that stimulation of K⁺ currents is responsible for GPR17‐induced oligodendrocyte differentiation. Moreover, we demonstrate, for the first time, that GPR17 activation stimulates OPC migration, suggesting an important role for this receptor after brain injury. Our data indicate that modulation of GPR17 may represent a strategy to potentiate the post‐traumatic response of OPCs under demyelinating conditions, such as multiple sclerosis, stroke, and brain trauma.     

和厚朴酚对小鼠背根神经节河豚毒素敏感型钠电流的影响

采用全细胞膜片钳技术,观察和厚朴酚(honokiol,Hnk)对急性分离的小鼠背根神经节上河豚毒素敏感型(TTX-S)钠电流及其通道动力学的影响,探讨Hnk可能的镇痛机制及作用靶点。结果显示:和厚朴酚浓度依赖性地抑制TTX-S钠电流,30 μmol/L和厚朴酚可以使稳态激活曲线向较正电压方向偏移达10.2 mV,通道失活后恢复时间明显延长,但对稳态失活动力学特征无明显的影响。