Fig. 4: CR enhances activity-dependent K⁺ release but shortens K⁺ transient.

a Astrocytic currents in response to voltage injections from −140 to 80 mV. Black—control, green—CR. b Mean curves of astrocytic current (I) in response to voltage injections (ΔV) in control (black) and in CR (green) mice. c The summary data are showing no difference in astrocyte input resistance (R_i) of control (black) and CR (green) mice. d A scheme illustrating the main mechanisms of the synaptically induced current in astrocyte. Presynaptically released glutamate triggers a current mediated by astrocytic transporters (I_GluT) and activates postsynaptic AMPA and NMDA receptors. K⁺ efflux through these receptors is responsible for most of I_K in the astrocyte (a small amount of I_K is released during action-potential propagation). e The protocol to estimate activity-dependent changes in I_K. Left, the astrocytic current induced by a single stimulus. Fast I_GluT is followed by slow I_K. Middle, the astrocytic current induced by five stimuli (black trace, 5 × 50 Hz) superimposed over the astrocytic current induced by four stimuli (orange trace, 4 × 50 Hz). Right, the current to fifth stimulus isolated by subtraction of the current to four stimuli from the current to five stimuli. f Representative currents to a single stimulus (dark traces) and the fifth stimulus (light traces) in control (gray) and CR (green) mice. g The summary plot is showing an increase in the I_K(5)/I_K(1) ratio in CR mice. Gray diamonds—control, green diamonds—CR mice. h The summary plot is showing a decrease in the τ_decay I_K(5)/τ_decay I_K(1) ratio in CR mice. Gray diamonds—control, green diamonds—CR mice. The data are presented as mean ± SEM; *p < 0.05; ***p < 0.001; two-sample t-test.