Korean J Physiol Pharmacol.  1997 Oct;1(5):495-504.

Regulation of AQP-4 water channel expression in the brain during development and by ischemia

• Jung JS
• Kim HG
• Bae HR
• Suh DJ
• Tae PH
• Lee SH

Abstract

Water transport is mediated by two distinct pathways, diffusional and channel-mediated water transport. The first molecular water channel was identified from human erythrocytes in 1992. Genetically-related proteins from other mammalian tissues have subsequently been identified to transport water, and the group is referred to as the "Aquaporins". Aquaporin-4 (AQP4) is most abundant in the brain, which may be involved in CSF reabsorption and osmoregulation. However, ontogeny and regulatory mechanisms of AQP4 channels have not been reported. Northern blot analysis showed that AQP4 mRNA began to be expressed in the brain just before birth and that its expression gradually increased by PN7 and then decreased at adult level. AQP4 was expressed predominantly in the ependymal cells of ventricles in newborn rats. And then its expression decreased in ependymal cells and increased gradually in other regions including supraoptic and paraventricular nuclei. AQP4 is also expressed in the subfornical organ, in which the expression level is not changed after birth. Cryogenic brain injury did not affect expression of AQP4 mRNA, while ischemic brain injury decreased it. Osmotic water permeability of AQP4 channel expressed in Xenopus oocytes was inhibited by the pretreatment of BAPTA/AM and calmidazolium, a Ca2+/ Calmodulin kinase inhibitor, in a dose-dependent manner. These
results
indicate that the expression and the function of AQP4 channel are regulated by developmental processes and various pathophysiological conditions. These results will contribute to the understanding of fluid balance in the central nervous system and the osrmoregulatory mechanisms of the body.

Keyword

Aquaporin-4; Regulation; Brain; Ischemia

MeSH Terms

Adult
Animals
Blotting, Northern
Brain Injuries
Brain*
Calcium-Calmodulin-Dependent Protein Kinases
Central Nervous System
Diffusion
Erythrocytes
Humans
Infant, Newborn
Ischemia*
Oocytes
Osmoregulation
Parturition
Permeability
Rats
RNA, Messenger
Subfornical Organ
Water*
Water-Electrolyte Balance
Xenopus
Calcium-Calmodulin-Dependent Protein Kinases
RNA, Messenger
Water