The metabotropic purinergic receptor agonist, UTP, elevates Ca²⁺ elevation and selectively activates a KCa3.1 current.

<p><b>A.</b> A representative Fura-2 recording from an MLS-9 cell (rat microglia cell line), in which 100 µM UTP was bath applied during the period marked by the horizontal bar. The inset shows how the Ca²⁺ signal was calibrated by adding ionomycin and MnCl₂, and as described in the Methods. <b>B.</b> The time course of the calibrated UTP-evoked Ca²⁺ rise (in µM) is shown for the cell in panel A. <b>C.</b> In whole-cell patch-clamp recordings, UTP evoked a large, transient current. From a holding potential of −70 mV, a voltage step to +50 mV was followed by a ramp from −100 to +80 mV applied every 5 sec. The two traces show the baseline control current (standard bath solution) and at the peak after adding 100 µM UTP. The reversal potential is indicated by the arrow. <b>D.</b> The time course of the current measured at +80 mV (same cell as panel C) is plotted on the same time scale as the Ca²⁺ signal in panel B. Vertical dashed lines indicate the time at which UTP was added. <b>E.</b> Comparison of the mean time to peak response after adding UTP for the Ca²⁺ signal and current activation. <b>F.</b> Comparison of the time course (half time) of the decay phase of the Ca²⁺ signal and current. <b>G.</b> UTP selectively activates a KCa3.1 current. The UTP-dependent current was quantified after subtracting the baseline from the maximal current (both at +80 mV) in the absence (control) or presence of the P₂Y₂ and P₂Y₆ receptor antagonist, 100 µM suramin. UTP-evoked currents were recorded in separate cells with the selective KCa3.1 blocker (1 µM TRAM-34) or the SK1–SK3 blocker (100 nM apamin) in the bath. The number of cells is indicated on each bar. ***<i>p</i><0.001