Ontogeny of water transport in the rabbit proximal tubule

Abstract

Water transport across cell membranes is a fundamental biological problem. In the kidney, many nephron segments have mechanisms for transporting large quantities of water with minimal energy input. The proximal tubule reabsorbs two-thirds of the glomerular filtrate with a small transepithelial osmotic gradient as the driving force. In the adult proximal tubule, this is accomplished by the expression of aquaporin 1 (AQP1), the water channel located on the apical and basolateral membranes of the proximal tubule. The neonatal tubule has a much lower expression of AQP1, yet can still transport water with a small osmotic gradient. Thus, tubule properties other than AQP1 expression must allow for this to occur. There are two primary differences that account for this unexpectedly high osmotic water permeability of the neonatal proximal tubule. First, the lipid membrane of the neonatal tubule is more fluid than the adult tubule and therefore a larger fraction of the water can pass through the lipid bilayer. The second property is the fact that the neonatal tubule cells have a smaller cell volume, and thus, the intracellular compartment provides less resistance for the movement of water. This review will discuss postnatal maturation of proximal tubule water transport.

Aquaporins in avian kidneys: function and perspectives

“…At birth, water is rapidly absorbed from the lungs in preparation for alveolar gas exchange in which AQP1 may have a role (52). In the juxtamedullary proximal convoluted tubules (PCT) from neonatal rabbits, expression of AQP1 is lower than in the adult PCT, whereas osmotic permeability of the PCT is approximately the same as in adults (96). This may suggest that tubule properties other than AQP1 expression may be important for neonatal PCT (96).…”

Anatomy, Physiology, and Behavior

“…This text will refer heavily to the previous work done by Cruise and Brewer as stated above. The epithelium of the proximal tubule is made up of a single layer of cells supported by a basement membrane (Quigley et al, 2003). Transitions between segments are gradual compared to other mammals such as the dog and rat (Kaissling and Kriz, 1979).…”

Glucocorticoids increase osmotic water permeability (Pf) of neonatal rabbit renal brush border membrane vesicles

“…This occurs in a nearly isoosmotic manner due to the high water permeability of this nephron segment provided by the abundance of aquaporin-1 (AQP1), the water channel in the kidney proximal tubule (1,18,26). The functional aspects of water transport in the proximal tubule during development have recently been studied and reviewed (21)(22)(23)(24)(25). In vitro microperfusion revealed that the osmotic water permeability coefficient (P f ) of the proximal tubule is higher in the neonatal rabbit than that in the adult (21).…”