PBFI, Tetraammonium Salt, cell impermeant

Selectivity Considerations and Cell Loading Strategies

The K_d 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). In buffers in which the Na⁺ is replaced by tetramethylammonium chloride, the K_d of PBFI for K⁺ is 11 mM; choline chloride and N-methylglucamine are two other possible replacements for Na⁺ in the medium. Although PBFI is only 1.5-fold more selective for K⁺ than for Na⁺, this selectivity is often sufficient because intracellular K⁺ concentrations are normally about 10 times higher than Na⁺ concentrations.

PBFI is available as both cell-impermeant acid salt (P1265MP) and as cell-permeant acetoxymethyl (AM) esters (P1267MP). The anionic acid forms can be loaded into cells using our Influx™ pinocytic cell-loading reagent (I14402, Chelators, Calibration Buffers, Ionophores and Cell-Loading Reagents—Section 19.8), or by microinjection, patch-pipette infusion or electroporation. For AM ester loading (Loading and Calibration of Intracellular Ion Indicators—Note 19.1), addition of the Pluronic™ F-127 (P3000MP, P6866, P6867) or PowerLoad™ (P10020) dispersing agents as well as relatively long incubation times—up to four hours—are typically necessary.

Find Fluorescent Indicators for Na⁺ and K⁺

We offer a number of fluorescent indicators for measuring Na⁺ and K⁺. Review Fluorescent Na+ and K+ Indicators—Section 21.1 in the Molecular Probes™ Handbook for more information on these products.

For Research Use. Not for human or animal therapeutic or diagnostic use.