The Journal of biological chemistry
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The M(3) muscarinic acetylcholine receptor (mAChR) expressed in HEK-293 cells couples to G(q) and G(12) proteins and stimulates phospholipase C (PLC) and phospholipase D (PLD) in a pertussis toxin-insensitive manner. To determine the type of G protein mediating M(3) mAChR-PLD coupling in comparison to M(3) mAChR-PLC coupling, we expressed various Galpha proteins and regulators of the G protein signaling (RGS), which act as GTPase-activating proteins for G(q)- or G(12)-type G proteins. ⋯ On the other hand, overexpression of RGS4, which acts on Galpha(q)- but not Galpha(12)-type G proteins, suppressed the M(3) mAChR-induced PLC stimulation without altering PLD stimulation. We conclude that the M(3) mAChR in HEK-293 cells apparently signals to PLD via G(12)- but not G(q)-type G proteins and that G protein subtype-selective RGS proteins can be used as powerful tools to dissect the pertussis toxin-resistant G proteins and their role in receptor-effector coupling.
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Hereditary non-X-linked nephrogenic diabetes insipidus (NDI) is caused by mutations in the aquaporin-2 (AQP2) water channel. In transfected cells, the human disease-causing mutant AQP2-T126M is retained at the endoplasmic reticulum (ER) where it is functional and targetable to the plasma membrane with chemical chaperones. A mouse knock-in model of NDI was generated by targeted gene replacement using a Cre-loxP strategy. ⋯ Kidneys from mutant mice showed collecting duct dilatation, papillary atrophy, and unexpectedly, some plasma membrane AQP2 staining. The severe phenotype of the AQP2 mutant mice compared with that of mice lacking kidney water channels AQP1, AQP3, and AQP4 indicates a critical role for AQP2 in neonatal renal function in mice. Our results establish a mouse model of human autosomal NDI and provide the first in vivo biochemical data on a disease-causing AQP2 mutant.
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Transthyretin (TTR) acts physiologically in the transport of retinol in the circulation. We previously reported the generation and partial characterization of TTR-deficient (TTR(-)) mice. TTR(-) mice have very low circulating levels of retinol and its specific transport protein, retinol-binding protein (RBP). ⋯ However, human retinol-RBP injected intravenously was more rapidly cleared from the circulation (t(12) = 0.5 h for TTR(-) versus t(12) >6 h for WT) and accumulated faster in the kidneys of TTR(-) compared with WT mice. The rate of infiltration of the retinol-RBP complex from the circulation to tissue interstitial fluids was identical in both strains. Taken together, these data indicate that low circulating retinol-RBP levels in TTR(-) mice arise from increased renal filtration of the retinol-RBP complex.
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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 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.