Resumo

HERNANDEZ, CS et al. Canales de Agua (Aquaporinas) y Riñón. AVFT [online]. 2002, vol.21, n.1, pp.8-15. ISSN 0798-0264.

This is a short overview of some aspects of water movements across kidney cells. It begins with the biophysical methods that lead to the conclusion that there are indeed water channels piercing the kidney proximal tubule cell membranes. These methods allow to calculate (a) the diameter of the selectivity filter of an "equivalent water channel" of ~ 4.5 Å, and (b) its "equivalent length" of ~ 10 - 20 Å. (c) As water molecules have a diameter of 3 Å, water molecules must line up within the selectivity filter as an Indian file 4 to 6 molecules long. Molecular biology studies have uncovered the aminoacid sequence of the 28 kDprotein molecules that form the water channels. They are called Aquaporins (AQPs). Some 10 are known. AQP-1 is present in the kidney proximal tubule. The tri-dimensional AQP-1 structure is reviewed, and the relation between diabetes insipidus and genetic structural failures of AQP-2 which lead to malfunction of the urinary concentrating mechanisms. Finally we review the molecular structure of a newly found AQP called RP-mip, which is present in Rhodnius prolixus malpighian tubules. A philogenetic tree indicates it to be one of the oldest AQPs. Mammalian AQPs are more recent in the biological scale.

Palavras-chave : Aquaporins; Water channels; Water pores; Water transport; Kidney water transport; Diabetes insipidus.