Abstract

Tanycytes are specialized glial cells that interact with hypothalamic peri-ventricular neurons of the arcuate nucleus; they express glucosesensing proteins, including glucose transporter 2, glucokinase (GK) and ATP-sensitive K+ (KATP) channels, indicating their involvement in hypothalamic glucosensing. Moreover intracellular GK localization is modulated by GK regulatory protein in tanycytes (GKRP). Here, we examined whether extracellular glucose modulates the intracellular free Ca2+ concentration (Ca2+signal) in cultured tanycytes. Measurements of intracellular Ca2+ signal (Fura-2: ratio 340/380) and hemichannel activity (ethidium uptake: time-lapse fluorescence intensity measurements) revealed that glucose increased the Ca2+ signal in a concentration-dependent manner and increased connexin 43 (Cx43) hemichannel activity. Glucose metabolism through GK limited this process since alloxan-induced GK inhibition significantly decreased the Ca2+ signal. In addition, the adenovirus-mediated GKRP overexpression decreased hemichannel activity promoted by glucose to agreater extent than by alloxan. On the other hand, extracellular glucose increased both GK and GKRP nuclear compartmentalization in primary cultures of tanycytes. These results suggest that in tanycytes activation of GK leads to the sequential and quick activation of Cx43 hemichannels, a process modulated by GKRP, followed by a rise in Ca2+ signal and cellular redistribution of glucose sensing proteins