Osmotic And Diffusive Water Permeabilities And Sieving Properties Of Aquaporin Water Channels (Wch) In Kidney Proximal (Pst) And Insect Upper Malpighian Tubules (Umt).

The functional existence of proteinic WChs can be inferred in a membrane when the following criteria hold: (a) if the ratio of the osmotic-to-diffusive water membrane permeabilities [PosRd] is >> 1; (b) if the control (non treated) Energies of Activation [E-act] of P-os and P-d are similar to 3-4 kcal/mole (as in free water movement); (c) if P., and Pd are curtailed by sulfhydryl reagents (Hg-containing agents like pCMBS or HgCl2) and (d) reverted by DTT towards their original values; (c) if under Hg-treatment [P-os/P-d] approaches 1; (f) and if the Hg-treated P-os and P-d E-act changed to >> 4 kcal/mole. Expression of WChs in cells that do not possess it (Xenopus loevis oocytes) was a gigantic step forward that led to the detailed WChs molecular characterization [1]. WChs, now called Aquaporins (AQPs), are recognized to form a family (AQP-1, -2, -3,..etc), with their amino acid sequences and three dimensional structures identified. Some of the AQPs are glycerol-permeable; others are not.Our experiments in rabbit PST, required design of original methods because of their very high P-os and P-d cell membrane values (P-os similar to 2553 mu m/sec). Following the criteria (a) to (f), our experiments demonstrated WCh function, and PST membrane sieving properties indicate they are glycerol impermeable. This WCh is now called AQP-1. [P-os/P-d] ratios led to conclude that water molecules single file within the PST AQP-1 molecules. Our experiments in the UNIT of the blood sucking insect Rhodnius prolixus also lead to conclude that they possess WChs. Molecular biology experiments demonstrate they are formed by a new molecule which we denote as Rp-MIP.