Fig. 1.
BK Ca2+-activated K+ current expression and currents in suprachiasmatic nucleus (SCN) neurons. A: BK current as a function of voltage. Values are the peak paxilline-sensitive current at each voltage normalized to cell capacitance (means ± SE). BK currents are larger at night in SCN neurons. *Day vs. night across voltages: P = 10−7, factorial ANOVA, n = 6 [day, zeitgeber time (ZT)4–7] and 10 (night, ZT17–20); Bonferroni post hoc, P < 0.05 at +10, 30, and 50 mV. B: nighttime-phased K+ current was revealed by application of 0.5 mM 4-aminopyridine (4-AP). Values are mean peak currents at +30 mV ± SE. Nighttime K+ currents were 23% larger than daytime. After subtraction of the BK current with 10 μM paxilline (+Pax), the day-night difference in the residual current was reduced to 16%, although the difference was not significant (interaction, P = 0.52, two-way ANOVA). C: BK is expressed throughout the SCN and colocalizes with the major SCN neurotransmitters. Coronal sections from WT SCN at ZT6–8 incubated with α-BK (red, middle) and α-vasoactive intestinal peptide (VIP; i), α-green fluorescent protein (GFP) marking GAD67-expressing (GABA-ergic) cells (ii), and α-arginine vasopressin (AVP; iii) in green.