Intracellular K+ is modulated by [K+]o level changes.

(A) Representative single-cell [K+]i trace during bath application of solutions with different K+ concentrations in the range 3 to 10 mM, as are found during physiological and pathological conditions. (B) Relationship between steady-state [K+]i (measured on plateau levels) and externally applied [K+]o (n = 120 cells from 12 exp). The graph indicates a steady increase in [K+]i in the [K+]o range 3–10 mM (plain circles), which yielded a slope of 1.04±0.06 (r = 0.82). A higher [K+]o of 15 mM (open circle) failed to further increase [K+]i. (C) Intracellular K+ is influenced by localized K+-gluconate puff applications. Representative [K+]i traces (average values of 7 cells each) during puff application (black arrows) of K+ gluconate in close proximity to the pipette (upper trace) and at>90 µm distance (lower trace). Insets: magnification of the trace after single extracellular applications of K+. Average amplitude (D) and duration of [K+]i rise (E) induced by K+ puffs (black bar) compared with responses observed in the presence of 200 µM Ba2+ (white bar) or 20 µM carbenoxolone (CBX, grey bar) (n = 62 cells, 5 exp). No significant changes in amplitudes were found, whereas the response duration was significantly prolonged by CBX and reduced by Ba2+.