Figure 1.

The MOR activation inhibits an outward current in whole cell current recording. (A) Traces of whole cell total current showing inward and outward currents under control conditions and after 1 μM DAMGO perfusion, the fast inward current (mainly attributable to Na⁺) did not change, but the outward current (attributable to K⁺) decreased significantly. Inset shows the fast inward current in a time expanded scale. The dotted lines indicate zero current. (B) The current-voltage relationship for the outward current showed a significant effect of DAMGO which decreased the maximum current 32% at 20 mV. (C) Concentration response relationship for the DAMGO inhibitory effect on the outward current was fitted with a Hill equation with a CI₅₀ = 600 nM and Hille coefficient of 1.2. (D) Voltage clamp recordings of whole cell current under control condition (black trace). The perfusion with a Ca²⁺ free extracellular solution significantly decreased the outward current (gray trace), and the effect of 1 μM DAMGO was completely occluded by perfusion with a Ca²⁺ free solution (blue trace). The dotted lines indicate zero current. (E) Time course of outward current amplitude in control, after 10 μM naloxone perfusion, which exerted no effect, but completely occluded the action of 1 μM DAMGO, indicating that DAMGO effect is specifically mediated by opioid receptor activation. ^*Indicates a significant difference P < 0.05.