Histamine H1 and H3 receptor activation increases the expression of Glucose Transporter 1 (GLUT-1) in rat cerebro-cortical astrocytes in primary culture

Abstract

Astrocytes take up glucose via the 45 kDa isoform of the Glucose Transporter 1 (GLUT-1), and in this work we have investigated whether histamine regulates GLUT-1 expression in rat cerebro-cortical astrocytes in primary culture. Cultured astrocytes expressed histamine H₁ and H₃ receptors (H₁Rs and H₃Rs) as evaluated by radioligand binding. Receptor functionality was confirmed by the increase in the intracellular concentration of Ca²⁺ (H₁R) and the inhibition of forskolin-induced cAMP accumulation (H₃R). Quantitative RT-PCR showed that histamine and selective H₁R and H₃R agonists (1 h incubation) significantly increased GLUT-1 mRNA to 153 ± 7, 163 ± 2 and 168 ± 13% of control values, respectively. In immunoblot assays, incubation (3 h) with histamine or H₁R and H₃R agonists increased GLUT-1 protein levels to 224 ± 12, 305 ± 11 and 193 ± 13% of control values, respectively, an action confirmed by inmunocytochemistry. The effects of H₁R and H₃R agonists were blocked by the selective antagonists mepyramine (H₁R) and clobenpropit (H₃R). The pharmacological inhibition of protein kinase C (PKC) prevented the increase in GLUT-1 protein induced by either H₁R or H₃R activation. Furthermore, histamine increased ERK-1/2 phosphorylation, and the effect of H₁R and H₃R activation on GLUT-1 protein levels was reduced or prevented, respectively, by MEK-1/2 inhibition. These results indicate that by activating H₁Rs and H₃Rs histamine regulates the expression of GLUT-1 by astrocytes. The effect appears to involve the phospholipase C (PLC) → diacylglycerol (DAG)/Ca²⁺→ PKC and PLC → DAG/Ca²⁺ → PKC → MAPK pathways.

Keywords: Astrocytes; GLUT-1; Glucose transport; Histamine; Histamine H(1) receptor; Histamine H(3) receptor.