In vitro increase in intracellular calcium concentrations induced by low or high extracellular glucose levels in ependymocytes and serotonergic neurons of the rat lower brainstem.

Pancreatic glucokinase (GK)-like immunoreactivities are located in ependymocytes and serotonergic neurons of the rat brain. The present study investigated in vitro changes in intracellular calcium concentrations ([Ca(2+)](i)) in response to low (2 mm) or high (20 mm) extracellular glucose concentrations in isolated cells from the wall of the central canal (CC), raphe obscurus nucleus (ROb), ventromedial hypothalamus (VMH), and lateral hypothalamic area (LHA) in male rats. An increase in [Ca(2+)](i) was found in cells from the CC (21.1% or 9.8% of ependymocytes), ROb (10.9% or 14.5% of serotonergic neurons), VMH (7.8% and 25.2% of neurons), and LHA (20% or 15.7% of neurons), when extracellular glucose levels were changed from 10 to either 2 or 20 mm, respectively. Most of the ependymocytes and serotonergic neurons responding to the glucose changes were immunoreactive to the anti-GK in the CC (96.8% for low glucose and 100% for high glucose) and ROb (100% for low and high glucose). The [Ca(2+)](i) increase was blocked with calcium-free medium or L-type calcium channel blocker. Cells with an increase in [Ca(2+)](i) in response to low glucose did not respond to high glucose and vice versa. Inhibition of GK activity with acute alloxan treatment blocked low or high glucose-induced [Ca(2+)](i) increases in most GK-immunoreactive cells from the CC or ROb. The glucose-sensitive [Ca(2+)](i) increase in neurons of the VMH and LHA was also alloxan-sensitive, but no cells taken from the VMH and LHA were immunoreactive to the antibody used. The present study further indicates that ependymocytes of the CC and serotonergic neurons in the ROb are also sensitive to the changes in extracellular glucose in a GK-dependent manner, but that the subtype of GK in these cells could be different from that in the VMH and LHA.