Figure 3: Ghrelin inhibits KCNQ current in nigral dopaminergic neurons.
From: Peptide hormone ghrelin enhances neuronal excitability by inhibition of Kv7/KCNQ channels
(a) Characterizations of KCNQ currents in SNc neurons by nystatin-perforated patch clamp recording using the standard deactivation protocol. KCNQ current showed characteristic inward relaxation when recorded from the holding potential of −20 to −30 mV and the time-dependent activation when stepped back to −20 mV. Dashed line indicates the current measured at −20 mV before the application of XE991. XE991 (30 μM) diminished the inward relaxation current caused by deactivation and elicited obvious baseline drops at −20 mV, reflecting the closure of KCNQ channels. (b) The enlarged subtracted trace of XE991-sensitive current calculated from a. (c) Left panel: the amplitude of KCNQ currents (IKCNQ) quantified from all SNc neurons held at −20 to −40 mV in the presence or absence of XE991. Right panel: IKCNQ was inhibited by 30 μM XE991 (n=5. Each bar represents the mean±s.e.m. *P<0.05, XE991 versus Control, t=2.186, Paired t-test.). (d) KCNQ currents recorded before, during and after application of ghrelin (100 nM, n=12). Ghrelin inhibited the KCNQ current in a reversible manner. (e) The enlarged subtracted trace of ghrelin-sensitive current (calculated from d) possesses the deactivation relaxation and activation kinetics of KCNQ current. (f) Left panel: IKCNQ quantified from all neurons recorded from a holding potential of −20 to −40 mV in the presence or absence of ghrelin. Right panel shows the statistical analysis of data from the left panel. IKCNQ was inhibited in the presence of 100 nM ghrelin (n=8. Each bar represents the mean±s.e.m. **P<0.01, Ghrelin versus Control, t=5.206, Paired t-test.). (g) XE991 abolished the excitatory effect of ghrelin. Both ghrelin and XE991 increased the firing rate. However, ghrelin (10 nM) failed to further increase firing rate in the presence of XE991 (1 μM). (h) A summary of statistical analysis for g. n=8. Each bar represents the mean±s.e.m. *P<0.05, Ghrelin versus Control; *P<0.05, XE991 versus Control; n.s., no significant difference, XE991 versus (XE991 + Ghrelin); F=3.452, ANOVA followed by S-N-K test.
