School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.
School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
Am J Physiol Endocrinol Metab. 2014 Jul 15;307(2):E161-75. doi: 10.1152/ajpendo.00446.2013. Epub 2014 May 27.
The plasma membrane potential (Vm) is key to many physiological processes; however, its ionic etiology in white fat adipocytes is poorly characterized. To address this question, we employed the perforated patch current clamp and cell-attached patch clamp methods in isolated primary white fat adipocytes and their cellular model 3T3-L1. The resting Vm of primary and 3T3-L1 adipocytes were -32.1 ± 1.2 mV (n = 95) and -28.8 ± 1.2 mV (n = 87), respectively. Vm was independent of cell size and fat content. Elevation of extracellular K(+) to 50 mM by equimolar substitution of bath Na(+) did not affect Vm, whereas substitution of bath Na(+) with the membrane-impermeant cation N-methyl-D-glucamine(+)-hyperpolarized Vm by 16 mV, data indicative of a nonselective cation permeability. Substitution of 133 mM extracellular Cl(-) with gluconate-depolarized Vm by 25 mV, whereas Cl(-) substitution with I(-) caused a -9 mV hyperpolarization. Isoprenaline (10 μM), but not insulin (100 nM), significantly depolarized Vm. Single-channel ion activity was voltage independent; currents were indicative for Cl(-) with an inward slope conductance of 16 ± 1.3 pS (n = 11) and a reversal potential close to the Cl(-) equilibrium potential, -29 ± 1.6 mV. Although the reduction of extracellular Cl(-) elevated the intracellular Ca(2+) of adipocytes, this was not as large as that produced by elevation of extracellular K(+). In conclusion, the Vm of white fat adipocytes is well described by the Goldman-Hodgkin-Katz equation with a predominant permeability to Cl(-), where its biophysical and single-channel properties suggest a volume-sensitive anion channel identity. Consequently, changes in serum Cl(-) homeostasis or the adipocyte's permeability to this anion via drugs will affect its Vm, intracellular Ca(2+), and ultimately its function and its role in metabolic control.
细胞膜电位 (Vm) 对许多生理过程至关重要；然而，其在白色脂肪细胞中的离子病因仍知之甚少。为了解决这个问题，我们在分离的原代白色脂肪细胞及其细胞模型 3T3-L1 中采用了穿孔片电流钳和细胞贴附片钳方法。原代和 3T3-L1 脂肪细胞的静息 Vm 分别为 -32.1 ± 1.2 mV（n = 95）和 -28.8 ± 1.2 mV（n = 87）。Vm 与细胞大小和脂肪含量无关。用 bath Na(+) 的等摩尔取代将细胞外液 K(+) 升高至 50 mM 不会影响 Vm，而用不透膜的阳离子 N-甲基-D-葡萄糖胺 (+) 取代 bath Na(+) 会使 Vm 超极化 16 mV，表明存在非选择性阳离子通透性。用葡糖酸盐取代 133 mM 细胞外 Cl(-) 会使 Vm 去极化 25 mV，而用 I(-) 取代 Cl(-) 会使 Vm 超极化 -9 mV。异丙肾上腺素（10 μM），而不是胰岛素（100 nM），显著去极化 Vm。单通道离子活性与电压无关；电流表明 Cl(-) 具有内向斜率电导为 16 ± 1.3 pS（n = 11），反转电位接近 Cl(-) 平衡电位，-29 ± 1.6 mV。虽然降低细胞外 Cl(-) 会增加脂肪细胞内的 Ca(2+)，但这不如升高细胞外 K(+) 产生的 Ca(2+)多。总之，白色脂肪细胞的 Vm 可以用 Goldman-Hodgkin-Katz 方程很好地描述，其主要通透性为 Cl(-)，其生物物理和单通道特性表明其为体积敏感的阴离子通道。因此，血清 Cl(-) 动态平衡的变化或药物对这种阴离子的通透性会影响其 Vm、细胞内 Ca(2+)，最终影响其功能及其在代谢控制中的作用。
