Intracellular K+ is modulated by glutamate application.

(A) Application of 200 µM glutamate induced a rapid and reversible [K+]i decrease with a amplitude of 2.3±0.1 mM (B) The [K+]i response to glutamate application in the range 0.1 µM to 10 mM followed a Michaelis and Menten kinetics with an apparent EC50 of 11.1±1.4 µM. (C) Simultaneous Na+ and K+ monitoring using SBFI and APG-1, respectively. SBFI was sequentially excited at 340 and 380 nm, and its fluorescence excitation ratio computed, and APG-1 was excited at 490 nm. Glutamate application (200 µM) is indicated in the graph. Exemplar single cell trace out of three experiments. (D) The fluorescent dye Fura-2 co-loaded with APG-1 was excited at 360 nm, its Ca2+-insensitive wavelength, whereas APG-1 was excited at 490 nm. Whereas 200 µM glutamate application caused a decline of the APG-1 fluorescence response, that of Fura-2 at 360 nm remained unperturbed (Exemplar trace out of two experiments).