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Expression and characterization of three aquaporins from a frog that accumulates glycerol in the cold.
Author(s) -
Goldstein David L.,
Krane Carissa M,
Frisbie James,
Zimmerman Sarah
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1395-a
Subject(s) - glycerol , aquaporin , chemistry , urea , xenopus , biochemistry , dehydration , acclimatization , biophysics , biology , botany , gene
During cold acclimation and freezing, gray treefrogs, Hyla chrysoscelis , accumulate and redistribute glycerol and water. We identified three aquaporins, HC‐1, 2, and 3, that may be involved in those processes. We expressed them in Xenopus oocytes and measured osmotic permeability (P f , as hypotonic swelling) and glycerol permeability (P g , from uptake of radiolabeled glycerol). HC‐1, 2, and 3 conferred P f of 121, 80, and 25 × 10 −4 cm/sec, respectively, and enhanced glycerol uptake 1.5, 1.5, and 2.5 times. Thus, relative enhancement of water:glycerol permeability was 87 times for HC‐1, 53 times for HC‐2, and 12 times for HC‐3. Along with analysis of critical amino acid residues, we identify HC‐1 and 2 as aquaporins‐proper (AQP), and HC‐3 as a glyceroporin (GLP). Cold (5°C vs 20°C) reduced P f most strongly for HC‐3 (50% reduction, vs. 10–20% for HC‐1 and 2), whereas P g was reduced in the cold for HC‐1 and 2 but not for HC‐3. qPCR indicated that mRNA for each aquaporin was expressed in tissue‐ and acclimation‐specific patterns that suggest roles in cold acclimation. Notably, HC‐3 was up‐regulated in the cold in liver (release of synthesized glycerol), muscle (uptake of circulating glycerol), and urinary bladder (conservation of urinary glycerol). Preliminary studies also indicate that HC‐3 facilitates urea transport; gray treefrogs accumulate some urea in response to dehydration but not cold. Supported by NSF IOB‐0517301.