PT - JOURNAL ARTICLE AU - S Saadoun AU - M C Papadopoulos AU - S Krishna TI - Water transport becomes uncoupled from K<sup>+</sup> siphoning in brain contusion, bacterial meningitis, and brain tumours: immunohistochemical case review AID - 10.1136/jcp.56.12.972 DP - 2003 Dec 01 TA - Journal of Clinical Pathology PG - 972--975 VI - 56 IP - 12 4099 - http://jcp.bmj.com/content/56/12/972.short 4100 - http://jcp.bmj.com/content/56/12/972.full SO - J Clin Pathol2003 Dec 01; 56 AB - 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+.