Appearance of Water Channels in <i>Xenopus</i> Oocytes Expressing Red Cell CHIP28 Protein

TLDR

Water traverses red blood cells and renal tubules through specialized, water‑selective channels whose molecular structure remains unknown, and the abundant integral membrane protein CHIP28—present in mammalian RBCs and renal proximal tubules—belongs to a family of proteins with uncharacterized functions. Microinjected Xenopus oocytes expressing CHIP28 RNA showed increased osmotic water permeability that was reversibly blocked by mercuric chloride, indicating that CHIP28 functions as a membrane water channel.

Abstract

Water rapidly crosses the plasma membrane of red blood cells (RBCs) and renal tubules through specialized channels. Although selective for water, the molecular structure of these channels is unknown. The CHIP28 protein is an abundant integral membrane protein in mammalian RBCs and renal proximal tubules and belongs to a family of membrane proteins with unknown functions. Oocytes from Xenopus laevis microinjected with in vitro-transcribed CHIP28 RNA exhibited increased osmotic water permeability; this was reversibly inhibited by mercuric chloride, a known inhibitor of water channels. Therefore it is likely that CHIP28 is a functional unit of membrane water channels.