Evidence that hindbrain astrocytes in the rat detect low glucose with a glucose transporter 2-phospholipase C-calcium release mechanism

Abstract

Astrocytes generate robust cytoplasmic calcium signals in response to reductions in extracellular glucose. This calcium signal, in turn, drives purinergic gliotransmission, which controls the activity of catecholaminergic (CA) neurons in the hindbrain. These CA neurons are critical to triggering glucose counter-regulatory responses (CRRs) that, ultimately, restore glucose homeostasis via endocrine and behavioral means. Although the astrocyte low-glucose sensor involvement in CRR has been accepted, it is not clear how astrocytes produce an increase in intracellular calcium in response to a decrease in glucose. Our ex vivo calcium imaging studies of hindbrain astrocytes show that the glucose type 2 transporter (GLUT2) is an essential feature of the astrocyte glucosensor mechanism. Coimmunoprecipitation assays reveal that the recombinant GLUT2 binds directly with the recombinant Gq protein subunit that activates phospholipase C (PLC). Additional calcium imaging studies suggest that GLUT2 may be connected to a PLC-endoplasmic reticular-calcium release mechanism, which is amplified by calcium-induced calcium release (CICR). Collectively, these data help outline a potential mechanism used by astrocytes to convert information regarding low-glucose levels into intracellular changes that ultimately regulate the CRR.