Figure 6: BK channels provoke an ionic imbalance through the activation of store-operated Ca²⁺ entry.

(a) Ten superimposed traces of the calcium fluorescence response of MG6 after 24 h of morphine (10 μM) stimulation. Closed and open bars indicate the application of 1 mM Ca²⁺ solution and Ca²⁺-free solution, respectively. Grey bars indicate the application of paxilline or LaCl₃, respectively. (b) The ratio of the 2nd/1st peak ΔF/F₀ responses (n=50/122/33 cells). (c) The measurement of the BDNF in the supernatant of MG6 following stimulation with morphine (10 μM) for 24 h. Naloxone (Nal, 10 μM), paxilline (Pax, 2 μM) or LaCl₃ (La³⁺, 50 μM) was added 1 h prior to morphine treatment (n=4 independent experiments). (d,f) Typical traces of the mEPSCs and root-evoked EPSCs recorded from the lamina I spinal neurons after 5 days of morphine administration in mice. TrkB-Fc (10 ng) and TrkB-Fc-h (heat-inactivated TrkB-Fc,10 ng) were intrathecally injected 1 h prior to morphine treatment. (e) The averaged frequency and amplitude of the mEPSCs (n=12 for TrkB-Fc, n=10 for TrkB-Fc-h, from three mice each). (g) The ratio of 2nd/1st peak currents (n=13 for TrkB-Fc, n=11 for TrkB-Fc-h, from three mice each). Orange and grey traces and columns indicate Morphine+TrkB-Fc (5d) and Morphine+TrkB-Fc-h (5d), respectively (d–g). The data represent the means±s.e.m. ***P=0.0001, 0.0001 (each column), F_{2, 201}=94.3, a one-way ANOVA followed by the Tukey’s post hoc test (b). **P=0.0016, 0.0073, 0.0035 (each column), ***P=0.0006, F_{4, 15}=9.351, a one-way ANOVA followed by the Tukey’s post hoc test (c). ***P=0.0005, t(20)=4.169 (e, left), P=0.0715, t(20)=1.904 (e, right), an unpaired t-test (e). **P=0.0013, t(22)=3.684, an unpaired t-test (g).