Fig. 5: BBR inhibits voltage-dependent potassium (Kv) currents, prolongs action potential durations (APDs), and promotes insulin exocytosis in mouse pancreatic islet β-cells.
From: Berberine is an insulin secretagogue targeting the KCNH6 potassium channel
a–e Total Kv currents in WT and Kcnh6 KO mouse pancreatic islet β-cells treated with 10 μM BBR or vehicle plus washout. a The total Kv currents of pancreatic islet β-cells expressing endogenous KCNH6 Kv channels and other endogenous Kv channels were measured in voltage-clamp mode. b Representative Kv currents were recorded from the indicated WT and KO β-cells. c–e Summary of the steady-state current-voltage (I–V) curves for Kv currents (upper panels) and the mean Kv current densities at +70 mV (lower panels) (WT, n = 8; WT + BBR, n = 8; WT + BBR + wash, n = 6; KO, n = 7; KO + BBR, n = 7; KO + BBR + wash, n = 4). P = 0.029 in (c), P = 0.023 in (d). f–i Action potentials in WT and KO pancreatic islet β-cells treated with 10 μM BBR or vehicle plus washout. f Representative action potentials were recorded from the indicated WT and KO β-cells in current-clamp mode. g–i Summary of the mean APDs (WT, n = 11; WT + BBR, n = 11; WT + BBR + wash, n = 7; KO, n = 14; KO + BBR, n = 13; KO + BBR + wash, n = 5). P = 0.005 in g, P = 0.008 in h. j–l Total internal reflection fluorescence (TIRF) microscopy analysis of pancreatic β-cells from WT mice. Islet β-cells expressing insulin-EGFP were incubated with 25 mM glucose for 30 min followed by the application of 10 μM BBR or control (DMSO). j TIRF images show live β-cells treated with the control or BBR. Red dots indicate the positions of exocytotic events occurring over 4 min after the application of BBR or the control. The white lines represent the outline of cells. Scale bars, 5 μm. A representative image from three different experiments is shown. k, l The average numbers of fusion events in control (n = 11 cells) and BBR-treated cells (n = 15 cells) at 1 min intervals are shown in k and are summed in l. P = 0.004 for 0–1 min, P = 0.004 for 1–2 min in k, P = 0.0005 in l. The values are presented as means ± s.e.m. *P < 0.05, **P < 0.01, and ***P < 0.001. Statistical significance was assessed using the Mann–Whitney U-test (two-sided).
