Lowering glucose level elevates [Ca²⁺]_i in hypothalamic arcuate nucleus NPY neurons through P/Q-type Ca²⁺ channel activation and GSK3β inhibition

Aim: To identify the mechanisms underlying the elevation of intracellular Ca²⁺ level ([Ca²⁺]_i) induced by lowering extracellular glucose in rat hypothalamic arcuate nucleus NPY neurons.
Methods: Primary cultures of hypothalamic arcuate nucleus (ARC) neurons were prepared from Sprague-Dawley rats. NPY neurons were identified with immunocytochemical method. [Ca²⁺]_i was measured using fura-2 AM. Ca²⁺ current was recorded using whole-cell patch clamp recording. AMPK and GSK3β levels were measured using Western blot assay.
Results: Lowering glucose level in the medium (from 10 to 1 mmol/L) induced a transient elevation of [Ca²⁺]_i in ARC neurons, but not in hippocampal and cortical neurons. The low-glucose induced elevation of [Ca²⁺]_i in ARC neurons depended on extracellular Ca²⁺, and was blocked by P/Q-type Ca²⁺ channel blocker ω-agatoxin TK (100 nmol/L), but not by L-type Ca²⁺ channel blocker nifedipine (10 μmol/L) or N-type Ca²⁺ channel blocker ω-conotoxin GVIA (300 nmol/L). Lowering glucose level increased the peak amplitude of high voltage-activated Ca²⁺ current in ARC neurons. The low-glucose induced elevation of [Ca²⁺]_i in ARC neurons was blocked by the AMPK inhibitor compound C (20 μmol/L), and enhanced by the GSK3β inhibitor LiCl (10 mmol/L). Moreover, lowering glucose level induced the phosphorylation of AMPK and GSK3β, which was inhibited by compound C (20 μmol/L).
Conclusion: Lowering glucose level enhances the activity of P/Q type Ca²⁺ channels and elevates [Ca²⁺]_i level in hypothalamic arcuate nucleus neurons via inhibition of GSK3β.