Fig. 2

Extracellular ATP increases K⁺ efflux from human microglia via THIK-1 and P2X7 receptors in a concentration-dependent manner. A Schematic illustrating the potentiation of THIK-1 K⁺ current via metabotropic coupling to high-affinity P2Y12 receptors, which transiently hyperpolarizes microglia to ~ − 60 mV. B Specimen outward THIK-1 current elicited by 100 µM ATP (left) showing rapid desensitization in the continued presence of ATP, analysed as residual current present 5 min after peak response (right). Mean current amplitude of ATP-evoked THIK-1 current was 19.25 pA ± 3.7 (n = 9). C Current profiles of a single microglia to voltage steps from − 150 mV to + 60 mV before and during application of 100 µM ATP (left) and respective voltage dependence of the net ATP-evoked THIK-1 current after subtracting (2) − (1) (right). Inset indicates the reversal potential of ~ − 85 mV, close to the predicted equilibrium potential for K⁺. D Effect of 5 µM C100814 on repeatedly evoked THIK-1 current by brief pulses of locally applied 100 µM ATP (left). Note suppression of the ATP-evoked and tonic THIK-1 current components (shaded area). Quantification of C100814-induced inhibition of ATP-evoked THIK-1 current, normalised to the mean outward current prior to drug application in the same cell (right). E Schematic showing ion channel pathways activated in microglia by exposure to high extracellular ATP concentration (> 1 mM). Additional activation of P2X7 cation channels, depolarizes microglia to ~ 0 mV, which concomitantly enhances K⁺ efflux via tonically active THIK-1 channels (dashed arrow) due to an increased driving force for K⁺. F Time course of microglial membrane current to 5 mM ATP at a holding potential of − 30 mV showing the emergence of a large sustained inward current that does not desensitize in the continued presence of ATP (left). Quantification of the ATP-evoked inward current 7 min after reaching steady state (2), normalised to current at time (1) when steady state was initially reached (right). Mean current amplitude of ATP-evoked P2X7 was − 103.42 pA ± 59.6 (n = 5). G Current profile of a single microglia to voltage steps from − 150 to + 60 mV before and during application of 5 mM ATP (left) and respective voltage-dependence of the net ATP-evoked P2X7 current after subtracting (2) − (1) (right). Inset indicates the reversal potential of ~ + 5 mV, close to the predicted equilibrium potential of a nonselective cation channel (P2X7). H Effect of 20 µM P2X7 antagonist A740003 on repeatedly evoked P2X7 current by brief pulses of locally applied 5 mM ATP at a holding potential of − 30 mV (left). Quantification of A74003-mediated inhibition of ATP-evoked P2X7 current, normalised to the mean inward current before drug application in the same cell (right). Data information: data indicate mean ± SEM. Dots on bars show number of cells. Data are from four individual patients. P-values are from paired Student’s t tests