ABSTRACT
Astrocyte swelling is observed in different types of brain injury including hepatic encephalopathy (HE). This study investigates the role of astrocyte swelling on Zn2+ homeostasis in hypoosmotically treated astrocytes by using the Zn2+ indicators Newport-Green, Zinquin, and RhodZin-3. Hypoosmolarity (205 mosmol/L) led to a persistent increase of the intracellular "free" Zn2+ concentration [Zn2+](i) within 15 min, which was reversible after reinstitution of normoosmolarity (305 mosmol/L). The hypoosmotic [Zn2+](i) increase was abolished in the presence of the Zn2+ chelator TPEN, the NMDA receptor antagonists MK-801 and AP5, the antioxidant epigallocatechin gallate, and the nitric oxide synthase inhibitors L-NMMA and TRIM. Hypoosmolarity triggered nuclear accumulation of the metal response element-binding transcription factor MTF-1 and the specificity protein Sp1 and expression of the mRNAs encoding metallothionein and the Sp1-regulated peripheral-type benzodiazepine receptor (PBR). These effects were abolished by the Zn2+ chelator TPEN. The data suggest that astrocyte swelling affects gene expression by modulation of [Zn2+](i). Whereas Zn2+-dependent upregulation of metallothionein may help to counteract excessive astrocyte swelling and production of reactive oxygen and nitrogen oxide species, stimulation of PBR expression may augment HE development.
