Fig. 2.

Selective and dose-dependent action of DPDPE on whole-cell Ba²⁺ currents in GLC8 cells.A, In A1, Ba²⁺ currents at +30 mV were recorded before (C), during (DPDPE), and after application of 0.3 μm DPDPE in 50 mm Ba²⁺. In A2and A3, the action of the μ-opioid-selective agonist DAMGO (1 μm) and the κ-opioid-selective agonist U50488 (1 μm) on Ba²⁺currents is compared with that of DPDPE (0.1 μm) on the same cell in 50 mm Ba²⁺. The sequential recordings were control (C), DPDPE, and the second agonist. In A4, the action of DPDPE (0.1 μm) was fully prevented by subsequent addition of the nonselective opioid antagonist naloxone (1 μm). Test depolarizations were to +30 mV from V_h −90 mV in all four panels. B, Effects of increasing doses of DPDPE (0.1, 0.3, 1, and 10 nm) on the Ba²⁺ currents of the same cell bathed in 10 mm Ba²⁺. Test depolarizations to +20 mV from V_h −90 mV.C, Percentage of Ba²⁺ current inhibition as a function of log [DPDPE] expressed in molar concentrations. Data points were collected from 20 GLC8 cells and plotted as mean ± SEM for n values as indicated. Thesolid line is a curve fit using equation:I_Ba inhibition (%) = 72/(1 + IC₅₀/[DPDPE]), with IC₅₀ = 0.64 nm.