Na+ / K+ 指示薬とイオノフォア

Find the best indicator and ionophore for imaging Na+ and K+


ナトリウム・チャネルおよびカリウム・チャネルは、イオン選択的なポア(細孔)を有する膜貫通型タンパク質で、そのポアの開閉によって細胞内へのイオン流出入と細胞の膜電位の維持・変化を調節しています。

代表的なポアの開閉の制御様式としては、以下の 2 種類があります。

  1. 電位依存性チャネル: 細胞膜の電位変化にしたがってポアが開閉
  2. リガンド依存性チャネル/イオン活性型チャネル: チャネル自体が受容体となり、リガンドまたはイオンが結合することによりポアが開閉

これらイオンチャンネルによる調節は、神経細胞同士、あるいは神経細胞と筋肉など他の組織との情報伝達に深く関与しており、イオンチャネルの働き、細胞内イオン濃度の変化を知ることは、細胞情報伝達を調べる上で役立ちます。アブカムはこのような試薬を各種取り揃えています。

Na+ indicators at a glance

IndicatorExcitation (nm)Emission (nm)Kd (mM)
Asante NaTRIUM Green488-51754020
SBFI340/3805054

Asante NaTRIUM Green

Asante NaTRIUM Green is a visible wavelength fluorescent indicator with a useful dynamic range for measuring cytosolic Na+ concentrations. Unlike SBFI, it loads readily into cells and is excited by visible light. Although Asante NaTRIUM Green excites maximally at 517 nm, its exceptional brightness enables excitation at the standard 488 nm settings used for the Fluo calcium indicators. Moreover, it works well for 2-photon excitation with near-infrared light. Asante NaTRIUM Green is also remarkable in its resistance to photobleaching and leakage.

SBFI

SBFI is an ultraviolet (340 and 380 nm) excitation ratiometric Na+ indicator used to estimate Na+ gradients in isolated mitochondria, to measure intracellular Na+ levels and Na+ efflux in cells, and, in combination with other fluorescent indicators used to correlate changes in intracellular Na+ with Ca2+ and Mg2+ concentrations. Although the selectivity of SBFI for Na+ is less than that of calcium indicators such as Fura-2, it is sufficient for the detection of physiological concentrations of Na+ in the presence of other monovalent cations. The spectral response of SBFI upon ion binding permit excitation ratio measurements, and this indicator can be used with the same optical filters and equipment used for Fura-2.


K+ indicators at a glance

IndicatorExcitation (nm)Emission (nm)Kd (mM)
Asante Potassium Green48854018
PBFI340/3905005

Asante Potassium Green

Asante Potassium Green is a fluorescent indicator with a useful Kd for measuring cytosolic K+ concentration. It loads readily and is excited by visible light. Although non-ratiometric, its large fluorescence dynamic range allows sensing of even small changes in K+ concentration. Optimal excitation occurs at 517 nm, but the indicator can also be excited at the conventional wavelength of 488 nm. Asante Potassium Green works well with 2-photon excitation at near-infrared wavelengths and although not fully resistant to photobleaching it is more robust than other dyes. Like its Na+ counterpart, it is useful for confocal microscopy, flow cytometry, and screening.

PBFI

PBFI is the K+ analog of the Na+ indicator SBFI. The Kd of PBFI for K+ is strongly dependent on whether Na+ is present, with a value of 5.1 mM in the absence of Na+ and 44 mM in solutions with a combined Na+ and K+ concentration of 135 mM (which approximates physiological ionic strength). Although the selectivity of PBFI for K+ is less than that of Ca2+ indicators such as Fura-2, it is sufficient for the detection of physiological concentrations of K+ in the presence of other monovalent cations. The spectral response of PBFI upon ion binding permit excitation ratio measurements, and this indicator can be used with the same optical filters and equipment used for Fura-2.

Na+ ionophores

Monensin sodium salt - Na+-selective carboxylic ionophore

SQI-Et (Na) - Effective at concentrations of ~ 40 µM

SQI-Pr (Na) - Effective at concentrations of 800-900 nM

SQI-Et and SQI-Pr have an intrinsic fluorescence that is excitable by UV light. Therefore, they are not well-suited for use with SBFI.

K+ ionophores

Valinomycin

Valinomycin is a natural, lipid-soluble molecule that binds potassium ions (K+) and facilitates their transfer across lipid bilayers. It exhibits a 10,000-fold selectivity for K+ over Na+. Valinomycin is a potent antibiotic. It is commonly used as an agent to induce apoptosis and can also be used to calibrate potentiometric responses in membrane experiments involving potential-sensitive dyes.

Nigericin

Nigericin is selective for both K+ and hydrogen ions (H+). Therefore it is commonly used in the fluorescence calibration of cytosolic pH indicators.

Nonactin

Monovalent cation ionophore that displays selectivity for K+ and NH4+ (K+ = NH4+ > Na+ > Mg2+ > Li+>> Ca2+). Induces cation transport across artificial membranes.

登録