Distribution of aquaporin-4 water channel expression within rat kidney

Terris, James; Ecelbarger, Carolyn A.; Marples, David; Knepper, Mark A.; Nielsen, Søren

doi:10.1152/ajprenal.1995.269.6.f775

Cited by 204 publications

(221 citation statements)

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“…5,21 Interestingly, this epithelium also expresses AQP4 on its basolateral domain, which is not under hormonal regulation. 22 AQP4 is unusual among aquaporins in that its water transporting properties are not inhibited by mercurial compounds such as HgCl 2 , 15 presumably because of the absence of a sensitive cysteine residue. We used this unique property of AQP4 to estimate its functional expression and contribution to total cholangiocyte membrane water permeability.…”

Section: Discussionmentioning

confidence: 99%

Expression of aquaporin-4 water channels in rat cholangiocytes

et al. 2000

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We recently reported that secretin induces the exocytic insertion of functional aquaporin-1 water channels (AQP1) into the apical membrane of cholangiocytes and proposed that this was a key process in ductal bile secretion. Because AQP1 is present on the basolateral cholangiocyte membrane in low amounts, we hypothesized that another AQP must be expressed at this domain to facilitate transbasolateral water movement. Thus, we investigated the expression, subcellular localization, possible regulation by secretin, and functional activity of AQP4, a mercury-insensitive water channel expressed in other fluid transporting epithelia. Using reverse transcription-polymerase chain reaction (RT-PCR) on RNA prepared from purified rat cholangiocytes, we amplified a product of 311 bp that was 100% homologous to the reported AQP4 sequence. RNase protection assay confirmed the presence of an appropriate size transcript for AQP4 in cholangiocytes. Immunoblotting detected a band of approximately 31 kd corresponding to AQP4 in basolateral but not apical membranes of cholangiocytes. Secretin did not alter the amount of plasma membrane AQP4 but, as expected, induced AQP1 redistribution from intracellular to apical plasma membranes. Functional studies showed that AQP4 accounts for about 15% of total cholangiocyte membrane water permeability. Our results indicate that: (1) cholangiocytes express AQP4 messenger RNA (mRNA) and protein and (2) in contrast to AQP1, which is targeted to the apical cholangiocyte membrane by secretin, AQP4 is constitutively expressed on the basolateral cholangiocyte membrane and is secretin unresponsive. The data suggest that AQP4 facilitates the basolateral transport of water in cholangiocytes, a process that could be relevant to ductal bile formation. (HEPATOLOGY 2000;31:1313-1317.)Cholangiocytes, or bile duct epithelial cells, account for secretin-induced ductal bile secretion. Cholangiocytes express aquaporin-1 (AQP1), a plasma membrane channel protein through which water moves passively in response to osmotic gradients. 1 We recently found that secretin induces the exocytic insertion of AQP1 specifically into the apical plasma membrane domain of cholangiocytes, a mechanism that seems to be key in ductal bile secretion 2-4 and is similar to the antidiuretic hormone (ADH)-induced insertion of AQP2 into the apical plasma membrane of the epithelial cells lining the kidney collecting duct. 5 The fact that AQP1 is present in the basolateral cholangiocyte membrane at only very low amounts 4 suggested to us that another member of the aquaporin family of proteins is expressed in the basolateral cholangiocyte domain. The basolateral expression of a water channel protein would facilitate the transbasolateral transport of water during bile secretion, fluid presumably derived from the closely apposed peribiliary vascular plexus. One candidate protein for this role is AQP4, initially called MIWC (for mercurial insensitive water channel). This water channel has been localized to the basolateral membranes of several flu...

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Section: Discussionmentioning

confidence: 99%

Expression of aquaporin-4 water channels in rat cholangiocytes

et al. 2000

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“…The antibody specific for hAQP5 was prepared as described (Terris et al, 1995). A synthetic peptide corresponding to the carboxy-terminus of hAQP5 (NH2-CEPDEDWEEQREERKKTMELTTR-COOH) (Lee et al, 1996) was cross-linked to keyhole limpet hemocyanin, and was used to immunize New Zealand white rabbits (Lofstrand Laboratories, Gaithersburg, Maryland).…”

Section: Antibodies To Haqp5mentioning

confidence: 99%

Abnormal Distribution of Aquaporin-5 Water Channel Protein in Salivary Glands from Sjögren's Syndrome Patients

Steinfeld

Cogan

King

et al. 2001

Laboratory Investigation

253

200

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“…AQP 3 permits the passage of water, glycerol and urea and is generally located to the basolateral membrane of epithelial cells (222)(223)(224)(225). AQP 4 is a mercury insensitive water channel also generally localized to the basolateral membranes of a variety of epithelial cells (226)(227)(228)(229)(230)(231). AQP 5 is localized to apical membranes, and is involved in the secretion of saliva, tears and pulmonary fluid (232,233).…”

Section: Aquaporinsmentioning

confidence: 99%