Ion channels and the regulatory mechanisms in different phenotypic mast cells derived from bone marrow hematopoietic stem cells

肥大呼叫起源于多电位造血干细胞，并在周围组织中分化为不同的表型，粘膜和结缔组织类型。最近的研究指出，腹膜肥大细胞（结缔组织型）和粘膜型肥大细胞的肿瘤类似物（RBL-2H3）中的离子通道有很大的不同。骨髓源性肥大细胞（BMMC）是通过小鼠骨髓细胞在肥大细胞生长因子存在下的体外培养获得的，在适当的微环境下，BMMC具有分化成不同表型的潜能。为了了解离子通道表达在肥大细胞增殖或分化中的意义，我们在全细胞钳形结构下记录了小鼠BMMC膜电流（Balb/c）。BMMC具有异质性的电生理特征，并根据20-24ºC的电流活动初步分为四个亚群：无电流活动的细胞（1型），向内整流K^+ (IR_K)电流（2型），向外整流Cl^- (OR_<Cl>)电流（3型）和向内加向外电流（4型）（Kuno等，in press）。在2型细胞中，膜电位在细胞间存在差异，并随着外部钾离子浓度的升高而趋于去极化。在3型细胞中，静息电位超极化与电导增加有关。因此，IR_K和OR_<Cl>通道都可能参与了膜电位的调节。我们还在1型细胞中观察到温度依赖的外向电流（初步观察），这意味着细胞内代谢变化可能调节BMMC通道的激活。我们认为，细胞周期、分化阶段和细胞内代谢的差异可能是BMMC离子通道活性异质性的基础。对单个离子通道调控机制的研究正在进行中。

Mast calls originate from multipotential hematopoietic stem cells and differentiate into different phenotypes, the mucosal and connective tissue types, in the peripheral tissues.Recent studies noted that ion channels in peritoneal mast cells (the connective tissue type) and a tumor analog of the mucosal type mast cells (RBL-2H3), were quite different.Bone marrow-derived mast cells (BMMC) obtained by an in vitro culture of mouse bone marrow cells in the presence of mast cell growth factors have a potency to differentiate into the different phenotypes in appropriate microenvironments.In order to understand significance of ion channel expression in either proliferation or differentiation of mast cells, membrane currents of mouse (Balb/c) BMMC were recorded under the whole cell clamp configuration.BMMC had a heterogeneous electrophysiological profile and were tentatively classified into four subpopulations according to the current activities at 20-24ﾟC : Cells with no current activity (type 1), inwardly rectifying K^+ (IR_K) currents (type 2), outwardly rectifying Cl^- (OR_<Cl>) currents (type 3) and inward plus outward currents (type 4) (Kuno, et al., in press).In the type 2 cells, the membrane potential varied among cells and tended to depolarize by elevating the external K^+ concentration.In the type 3 cells, the resting potential was hyperpolarized in association with an increase in the conductance.Thus both the IR_K and OR_<Cl> channels are likely to contribute to the regulation of the membrane potential.We also observed temperature-dependent outward currents even in the type 1 cells (preliminary observations), which implicates that intracellular metabolic changes may regulate activation of channels in BMMC.We suggest that differences in cell cycles, stages of differentiation and intracellular metabolisms may underlie the heterogeneity in ion channel activities in BMMC.Studies on regulatory mechanisms of individual ion channels are going on.