Gene cloning and expression of an aquaporin (AQP-h3BL) in the basolateral membrane of water-permeable epithelial cells in osmoregulatory organs of the tree frog

Abstract

Akabane G, Ogushi Y, Hasegawa T, Suzuki M, Tanaka S. Gene cloning and expression of an aquaporin (AQP-h3BL) in the basolateral membrane of water-permeable epithelial cells in osmoregulatory organs of the tree frog. Am J Physiol Regul Integr Comp Physiol 292: R2340-R2351, 2007. First published March 1, 2007; doi:10.1152/ajpregu.00905.2006.-An aquaporin (Hyla AQP-h3BL), consisting of 292 amino acid residues, has been cloned from the urinary bladder of Hyla japonica. In a swelling assay using Xenopus oocytes, AQP-h3BL cRNA-injected oocytes developed a sevenfold and 2.8-fold higher permeability to water and glycerol, respectively, than the water-injected oocytes. This permeability was inhibited by HgCl 2. Immunofluorescence revealed that AQP-h3BL is localized in the basolateral plasma membrane of both granular cells in the ventral pelvic and dorsal skins and the secretory cells in the mucous glands. Immunopositive cells were also observed in the basolateral membrane of principal cells in the collecting ducts and in a portion of the late distal tubules in the kidneys, as well as in the principal cells of the urinary bladder. Sequence homology suggests that AQP-h3BL is a homolog to mammalian AQP3. This conclusion is supported by the observed localization of AQP-h3BL to the basolateral membrane in water-and glycerol-permeable epithelial cells. In ventral pelvic skins and urinary bladders, water enters into the cytoplasm through the apical plasma membrane at sites where AQP-h2, sometimes in association with AQP-h3, responds to stimulation by vasotocin; the water exits throughout AQP-h3BL to extracellular spaces. In the mucous glands, on the other hand, water enters throughout this AQP-h3BL and exits through AQP-x5, which is in the apical membrane of secretory cells. Thus, water homeostasis in the frog body is regulated by AQP-h3BL expressed in the basolateral membrane in concert with arginine vasotocin (AVT)-dependent or AVT-independent AQP. skin; urinary bladder; kidney; mucous gland; arginine vasotocin; immunocytochemistry; anuran amphibian PRESENT-DAY AMPHIBIANS ARE representative of the first vertebrates that made the transition from aquatic habitats to terrestrial environments. To adapt to these drier environments, many adult anurans have evolved specialized osmoregulatory organs that consist of a ventral pelvic skin capable of absorbing water from the external environment and a urinary bladder that stores water and reabsorbs it in times of need. The neurohypophyseal hormone arginine vasotocin (AVT), the nonmammalian vertebrate counterpart of vasopressin, stimulates these organs, thereby facilitating water absorption in many anuran species (2). The classic concept of this process was diffusion of water through the lipid bilayer of plasma membrane. However, biophysical and physiological studies predicted that water movement occurs through membrane channel proteins (3), and during the early 1990s, such water channel proteins were indeed discovered. These were given the name aquaporins (AQPs) (1), and they have been...

Correlation between aquaporin and water permeability in response to vasotocin, hydrin and β-adrenergic effectors in the ventral pelvic skin of the tree frogHyla japonica

“…However, there was no significant difference among the AVT-, hydrin 1-and hydrin 2-treated groups. In each of the histological sections from the control group, labels for AQP-h2 and AQP-h3 were observed near or in the basolateral membrane in the FRC layer whereas the label for AQP-h3BL, which is expressed constitutively in the basolateral plasma membrane (Akabane et al, 2007), was visible at the same sites (Fig.5A-C). In the AVT-, hydrin 1-and hydrin 2-treated groups, however, labels for AQP-h2 and AQP-h3 were intensely visible in the apical plasma membrane of the principal cells in the FRC layer (Fig. 5D,E,G,H,J,K).…”

“…In brief, for the doubleimmunofluorescence labeling of AQP-h2 and AQP-h3, sections were incubated with a mixture of guinea pig anti-AQP-h2 [ST-140; 1:5,000 (Hasegawa et al, 2003)] and rabbit anti-AQP-h3 [ST-141; 1:10,000 (Tanii et al, 2002)], and then reacted with a mixture of indocarbocyanine (Cy3)-labeled donkey anti-guinea pig IgG (1:400; Jackson Immunoresearch, West Grove, PA, USA), Alexa 488-labeled donkey anti-rabbit IgG (1:200; Molecular probes, Eugene, OR, USA) and DAPI. Rabbit anti-Hyla AQP-h3BL serum (ST-184) was also used for labeling the basolateral membrane of the principal cells (Akabane et al, 2007). Specimens were examined with an Olympus BX61 microscope equipped with a BX-epifluorescence attachment (Olympus Optical Co., Tokyo, Japan).…”

Tubular localization and expressional dynamics of aquaporins in the kidney of seawater-challenged Atlantic salmon

“…A signal for Aqp3a was also seen in the sub-apical space, suggesting a role in volume regulation of intracellular vesicles, which are plentiful in the proximal tubules of rainbow trout (Anderson and Loewen 1975), in addition to trans-cellular water exchange (secretion). In amphibians, reptiles, birds and mammals, AQP3 is found in basolateral membranes of late distal and collecting ducts as well as the urinary bladder of the tree frog (Nielsen et al 2002;Akabane et al 2007;Babonis et al 2011;Nishimura and Yang 2013). This apparent shift in cellular/sub-cellular localization from teleosts to terrestrial vertebrates may be due to the increased need for water reabsorption in the latter as well as the more specialized architecture of the metanephric kidneys of birds and mammals.…”

The water-absorption region of ventral skin of several semiterrestrial and aquatic anuran amphibians identified by aquaporins

“…This tissue distribution of AQP-h2 and AQP-h3 isoforms is provided in Table 1. A subfamily of AQPs, termed aquaglyceroporins occurs in the basolateral membranes of water-transporting epithelia (1,17) and is permeated by glycerol and urea in addition to water. In amphibians, these include AQP-h3BL, homologue of mammalian AQP3, in H. japonica (2), and AQP HC-3 in H. chrysoscelis (37). Such channels facilitate the movement of water out of the cells into the vasculature, but the rate-limiting step is apical entry that is regulated by AVT and possibly other factors.…”