Aquaporin-1 is expressed by vascular smooth muscle cells and mediates rapid water transport across vascular cell membranes

The aquaporins are a rapidly expanding family of highly conserved proteins which function as transmembrane water channels. We have previously shown that the gene for aquaporin-1 (AQP-1) is expressed in rat, aortic vascular smooth muscle cells (VSMCs) implying a specific role for AQP-1 in vascular function. In this study we set out to document the expression of AQP-1 in human arteries and found mRNA and protein in normal endothelial and VSMCs of human arteries and capillaries and in a subset of VSMCs in human atherosclerotic plaques. Secondly, we examined the regulation of AQP-1 gene expression during vascular development and following vascular injury. Studies in the rat demonstrated that AQP-1 mRNA is induced in the neonatal aorta at week 2 of postnatal development and that the protein is present in neointimal VSMCs following balloon injury. Finally, by measuring the rate of change in cell size induced by changes in external osmolarity and demonstrating that water transport can be inhibited with mercuric chloride, we show that AQP-1 is responsible for water transport across human VSMC membranes. Thus, this study provides evidence for a hitherto unrecognised role for aquaporins in mediating rapid water transport across human VSMC membranes. By analogy with other tissues, these data argue for an important role for AQP-1 in regulating transcellular fluid flow and tissue hydration.