TY - JOUR T1 - Water transport becomes uncoupled from K<sup>+</sup> siphoning in brain contusion, bacterial meningitis, and brain tumours: immunohistochemical case review JF - Journal of Clinical Pathology JO - J Clin Pathol SP - 972 LP - 975 DO - 10.1136/jcp.56.12.972 VL - 56 IS - 12 AU - S Saadoun AU - M C Papadopoulos AU - S Krishna Y1 - 2003/12/01 UR - http://jcp.bmj.com/content/56/12/972.abstract N2 - Specimens of normal human brain, contused brain, brain with bacterial meningitis, and brain tumours were immunolabelled for aquaporin 4 (AQP4) and Kir4.1. In normal brain tissue, AQP4 and Kir4.1 were detected around the microvessels. In pathological brain tissue, AQP4 was upregulated in astrocytes in oedematous regions and Kir4.1 was upregulated in astrocytes in damaged brain. Changes in α syntrophin expression paralleled those of AQP4 and Kir4.1. The following hypothesis is proposed: in astrocytes, under normal conditions, AQP4 couples water transport with Kir4.1 mediated K+ siphoning, but in pathological states, AQP4 facilitates the flow of brain oedema fluid, and Kir4.1 buffers increased extracellular K+. ER -