Erythrocyte Water Permeability and Renal Function in Double Knockout Mice Lacking Aquaporin-1 and Aquaporin-3

Baoxue Yang,Tonghui Ma,A.S Verkman

doi:10.1074/jbc.m008664200

Baoxue Yang, Tonghui Ma + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m008664200

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Abstract

Aquaporin (AQP) water channel AQP3 has been proposed to be the major glycerol and non-AQP1 water transporter in erythrocytes. AQP1 and AQP3 are also expressed in the kidney where their deletion in mice produces distinct forms of nephrogenic diabetes insipidus. Here AQP1/AQP3 double knockout mice were generated and analyzed to investigate the functional role of AQP3 in erythrocytes and kidneys. 53 double knockout mice were born out of 756 pups from breeding double heterozygous mice. The double knockout mice had reduced survival and impaired growth compared with the single knockout mice. Erythrocyte water permeability was 7-fold reduced by AQP1 deletion but not further reduced in AQP1/AQP3 null mice. AQP3 deletion did not affect erythrocyte glycerol permeability or its inhibition by phloretin. Daily urine output in AQP1/AQP3 double knockout mice (15 ml) was 9-fold greater than in wild-type mice, and urine osmolality (194 mosm) was 8.4-fold reduced. The mice remained polyuric after DDAVP administration or water deprivation. The renal medulla in most AQP1/AQP3 null mice by age 4 weeks was atrophic and fluid-filled due to the severe polyuria and hydronephrosis. Our data provide direct evidence that AQP3 is not functionally important in erythrocyte water or glycerol permeability. The renal function studies indicate independent roles of AQP1 and AQP3 in countercurrent exchange and collecting duct osmotic equilibration, respectively.

Highlights

The route for water movement across the erythrocyte plasma membrane has been a subject of longstanding interest
Ͼ90% of living AQP1 and AQP3 null mice that were genotyped at 5 days remained alive at 8 weeks, only 50% of the double knockout mice were alive at 8 weeks
Erythrocyte glycerol permeability was not affected by AQP3 deletion nor was the inhibition of glycerol permeability affected by phloretin

Summary

Introduction

The route for water movement across the erythrocyte plasma membrane has been a subject of longstanding interest. The principal goal of this study was to determine the functional role of AQP3 in erythrocyte water and glycerol permeability. Mice lacking AQP1 are polyuric and have urine osmolalities of 500 –700 mosM that do not increase after water deprivation or DDAVP administration [3]. AQP3 null mice are remarkably polyuric with base-line urine osmolalities of Ͻ280 mosM but are able to concentrate their urine to 1000 –1400 mosM after water deprivation or DDAVP administration. A comparison of water and glycerol permeabilities of erythrocytes from the single and double knockout mice permitted a direct assay of the functional role of AQP3. A comparison of urinary-concentrating ability in the single and double knockout mice tested whether the different patterns of nephrogenic diabetes insipidus result from distinct defects in countercurrent exchange and collecting duct function

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