The Impact of Astrocytic Gap Junctional Coupling on Potassium Buffering in the Hippocampus

Recovery of stimulation-induced increase of [K⁺]_o in stratum pyramidale is slower in dko mice. A, Decline of representative, matched [K⁺]_o transients after stimulus trains (20 Hz) evoked with high (wt, 100%; dko, 75%) and low (wt and dko, 50%) stimulus intensity. For the wt traces, t_1/e (the time after which [K⁺]_o amplitude has decayed to 1/e of its initial value) is indicated. Note that decay is faster for larger rises in [K⁺]_o (dotted line, t_1/e = 1.93 s; dashed line, t_1/e = 2.35 s). B, t_1/e values of [K⁺]_o recovery after a stimulus train (20 Hz; 25, 50, 75, and 100% stimulation intensities) plotted against [K⁺]_o at the end of the stimulus (wt, open diamonds; dko, filled squares). The inverse relationships between [K⁺]_o and t_1/e were best described by a power function (thin line for wt, y = 5.272x exp(−0.417); thick line for dko mice, y = 6.068x exp(−0.412). y-axis intercepts differed significantly (asterisk; see Results). C, Semilogarithmic plots of the decline of representative, matched [K⁺]_o transients (from 90% to the trough of the undershoot; gray dots) after 100% stimulus trains (20 Hz). Top, wt; bottom, dko. Two exponential components contribute to this decline and are plotted individually (straight black lines; wt, τ_fast = 1.46 s, τ_slow = 11.3 s; dko, τ_fast = 1.15 s, τ_slow = 10.5 s). Their sum provides an excellent fit of the data (black curves). Note that the relative amplitude of τ_fast (τ_fast amplitude fraction) is larger in the wt (84%) compared with the dko [K⁺]_o decay (70%). D, τ_fast amplitude fractions plotted against [K⁺]_o at the end of the stimulus (wt, open diamonds; dko, filled squares). The linear relationship was significantly (asterisk) shifted toward smaller τ_fast amplitude fractions in dko mice (thin line, wt, linear equation: y = 0.0445x + 0.39; thick line, dko, y = 0.0346x + 0.38).