Glucocorticoids increase osmotic water permeability (P<sub>f</sub>) of neonatal rabbit renal brush border membrane vesicles

Mulder, Jaap; Chakravarty, Sumana; Haddad, Maha; Baum, Michel; Quigley, Raymond

doi:10.1152/ajpregu.00448.2004

Cited by 12 publications

(11 citation statements)

References 36 publications

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“…Blunted synthesis in the medullary and cortical collecting tubule [352] The postnatal increase in glucocorticoids is a likely factor in mediating the above noted maturational changes in water permeability and aquaporin 1 expression. Administration of glucocorticoids to neonatal rabbits resulted in an increase in brush border membrane water permeability and aquaporin 1 expression [226]. Of interest, the developmental increase in thyroid hormone was not shown to be a factor mediating these postnatal maturational changes in water transport [227].…”

Section: Developmental Features Of Proximal Tubule Water Transportmentioning

confidence: 99%

“…Direct measurements of water permeability have demonstrated that the neonatal rabbit proximal tubule has a higher water permeability than that of the adult [222]. To determine the mechanism for the higher water permeability in neonatal rabbit tubules, studies were performed examining the water permeability of apical and basolateral membrane vesicles [223][224][225]. Despite the higher transepithelial water permeability, the water permeability of the apical and basolateral membrane was lower in the neonate than the adult and there was less aquaporin 1 expression on both the apical and basolateral membranes of the proximal tubule of the neonate [224,225].…”

Section: Developmental Features Of Proximal Tubule Water Transportmentioning

confidence: 99%

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Renal Tubular Development

Baum

2014

Pediatric Nephrology

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The nephron is faced with the enormous task of maintaining a constant composition and volume of the extracellular fluid. The amount of electrolytes and water ingested and absorbed must be eliminated, and the waste products from metabolism must also be excreted. This challenge is all the more complex as our dietary intake is quite variable from day to day. Despite this variable intake, there is virtually no change in the volume or composition of the extracellular fluid volume from day to day.There are two possible ways that our kidney could balance ingestion and excretion. The kidney could be a secretory organ where all the excess solutes and water ingested would be excreted by tubular secretion. This would be very inefficient and require an enormous amount of energy. In addition, in times of a disturbance in the extracellular fluid volume such as a high salt intake or volume loss from diarrhea, the regulatory systems necessary to maintain a constant extracellular fluid volume and composition while excreting waste products would be very complex. On the other hand, the kidney could filter an enormous quantity of extracellular fluid, which would be very efficient in removing waste products, and reclaim the desired salt, organic solutes, and water. With volume depletion, a greater fraction of salt and water could be reabsorbed, and when one has a dietary indiscretion such as the salt intake from a pepperoni pizza, there could be a reduction in sodium reabsorption leading to an increase in excretion to bring us back into balance. The mammalian kidney actually uses both mechanisms to perform its job which is necessary for our survival on land. The adult kidney filters~150 l of isotonic fluid a day and reclaims most of it, leaving the waste produces to be excreted in about 1.5 l of urine. In addition, there are secretory processes for solutes such as organic anions and cations in the proximal tubule and secretory mechanisms to excrete the excess acid generated from metabolism in the distal nephron which aid in maintaining homeostasis.To accomplish the remarkable task of reclamation of the necessary solutes and water to maintain a constant composition of the extracellular fluid volume, the mammalian kidney has evolved into a highly specialized organ with thousands of units called nephrons. Each human kidney has approximately one million nephrons. Each nephron is a tube consisting of epithelial cells and is divided into 12 specialized segments as shown in Fig. 1. The epithelial cells allow for the vectorial transport of solutes. The proximal tubule is responsible for the bulk reclamation of solutes and water and for the secretion of organic cations and anions. Approximately two-thirds of the glomerular filtrate is reabsorbed by the proximal tubule in an isotonic fashion. Virtually all of the organic solutes, as well as the majority of bicarbonate, phosphate, and chloride, are reabsorbed in this segment. The proximal tubule is divided into S 1 , S 2 , and S 3 segments based on the rates of transport of some solutes and mor...

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Section: Developmental Features Of Proximal Tubule Water Transportmentioning

confidence: 99%

Section: Developmental Features Of Proximal Tubule Water Transportmentioning

confidence: 99%

Renal Tubular Development

Baum

2014

Pediatric Nephrology

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“…In subsequent studies, we have directly measured the neonatal and adult BBMV fluidity using the fluorophore, laurdan [20,21]. These results indicate that the membrane fluidity of the neonatal renal BBMV is indeed higher than the adult BBMV.…”

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confidence: 93%

“…14 C-n-butanol and 3 H-water were placed in the perfusion solution to measure n-butanol permeability (P DNB ) and diffusional water permeability (P DW ) simultaneously. Reproduced with permission from reference [21] The last component of the transepithelial pathway to be examined was the paracellular pathway. This component is difficult to examine directly so indirect methods were employed.…”

mentioning

confidence: 99%

“…4). Reproduced with permission from reference [21] a Calculated epithelial PCT P f was determined from the apical and basolateral membrane P f measurements and surface areas b Measured epithelial PCT P f is from experimental measurement of the tubule P f and is from reference [18] c Calculated intracellular PCT P f is from the relationship: to water flow. When the intracellular compartment is placed in series with the membranes, the calculated permeability of the intracellular compartment is 2.8× 10 −4 cm 2 /s.…”

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Ontogeny of water transport in the rabbit proximal tubule

Quigley

Mulder

Baum

2003

Pediatric Nephrology

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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.

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