Focus on "rapid entry of bitter and sweet tastants into liposomes and taste cells: implications for signal transduction"

A highly-occupied, single-cell trapping microarray for determination of cell membrane permeability

Semi- and selective permeability is a fundamentally important characteristic of the cell membrane. Membrane permeability can be determined by monitoring the volumetric change of cells following exposure to a non-isotonic environment. For this purpose, several microfluidic perfusion chambers have been developed recently. However, these devices only allow the observation of one single cell or a group of cells that may interact with one another in an uncontrolled way. Some of these devices have integrated on-chip temperature control to investigate the temperature-dependence of membrane permeability, but they inevitably require sophisticated fabrication and assembly, and delicate temperature and pressure calibration. Therefore, it is highly desirable to design a simple single-cell trapping device that allows parallel monitoring of multiple separate, individual cells subjected to non-isotonic exposure at various temperatures. In this study, we developed a pumpless, single-layer microarray with high trap occupancy of single cells. The benchmark performance of the device was conducted by targeting spherical particles of 18.8 μm in diameter as a model, yielding trap occupancy of up to 86.8% with a row-to-row shift of 10-30 μm. It was also revealed that in each array the particles larger than a corresponding critical size would be excluded by the traps in a deterministic lateral displacement mode. Demonstrating the utility of this approach, we used the single-cell trapping device to determine the membrane permeability of rat hepatocytes and patient-derived circulating tumor cells (Brx-142) at 4, 22 and 37 °C. The membrane of rat hepatocytes was found to be highly permeable to water and small molecules such as DMSO and glycerol, via both lipid- and aquaporin-mediated pathways. Brx-142 cells, however, displayed lower membrane permeability than rat hepatocytes, which was associated with strong coupling of water and DMSO transport but less interaction between water and glycerol. The membrane permeability data reported here provide new insights into the biophysics of membrane transport such as aquaporin expression and coupling transport of water and solutes, as well as providing essential data for the ultimate goal of biobanking rare cells and precious tissues.

Membrane water permeability of maize root cells under two levels of oxidative stress

Changes in the total water permeability of two cell membranes (plasmalemma and tonoplast), estimated by the effective diffusion coefficient of water (D ef), were controlled using the NMR method. The time dynamics of D ef in maize (Zea mays L.) root cells was studied in response to (i) root excision from seedling and the following 6-h incubation in the growth medium (wound stress) and (ii) the superposition of wound stress plus paraquat, which induces the excess of reactive oxygen species (ROS). The dynamics of lipid peroxidation, oxygen consumption, and heat production was studied to estimate general levels of oxidative stress in two variants of experiments. Under wound stress (the weak oxidative stress), the reversible by dithiothreitol increase in cell membrane water permeability was observed. The applicability of mercury test to aquaporin activity in our experiments was verified. The results of wound stress effect, obtained using this test, are discussed in terms of oxidative upregulation of aquaporin activity by ROS. The increase of oxidative stress in cells (wound-paraquat stress), contrary to wound stress, was accompanied by downregulation of membrane water permeability. In this case, ROS is supposed to affect the aquaporins not directly but via such processes as peroxidation of lipids, inactivation of some intracellular proteins, and relocalization of aquaporins in cells.

Influence of ester-modified lipids on bilayer structure

Lipid membranes function as barriers for cells to prevent unwanted chemicals from entering the cell and wanted chemicals from leaving. Because of their hydrophobic interior, membranes do not allow water to penetrate beyond the headgroup region. We performed molecular simulations to examine the effects of ester-modified lipids, which contain ester groups along their hydrocarbon chains, on bilayer structure. We chose two lipids from those presented in Menger et al. [J. Am. Chem. Soc. 2006, 128, 14034] with ester groups in (1) the upper half of the lipid chain (MEPC) and (2) the middle and end of the lipid chain (MGPC). MGPC (30%)/POPC bilayers formed stable water pores of diameter 5-7 Å, but MGPC (22%)/POPC and MEPC (30%)/POPC bilayers did not form these defects. These pores were similar to those formed during electroporation; i.e., the head groups lined the pore and allowed water and ions to transport across the bilayer. However, we found that lateral organization of the MGPC lipids into clusters, instead of an electric field or charge disparity as in electroporation, was essential for pore formation. On the basis of this, we propose an overall mechanism for pore formation. The similarities between the ester-modified lipids and byproducts of lipid peroxidation with multiple hydrophilic groups in the middle of the chain suggest that free radical reactions with unsaturated lipids and sterols result in fundamental changes that may be similar to what is seen in bilayers with ester-modified lipids.

Adaptive evolution of the osmoregulation-related genes in cetaceans during secondary aquatic adaptation

Background

Osmoregulation was a primary challenge for cetaceans during the evolutionary transition from a terrestrial to a mainly hyperosmotic environment. Several physiological mechanisms have been suggested to maintain the water and salt balance in cetaceans, but their genetic and evolutionary bases remain poorly explored. The current study investigated the genes involved in osmoregulation in cetaceans and compared them with their counterparts in terrestrial mammals to test whether adaptive evolution occurred during secondary aquatic adaptation.

Results

The present study analyzed the molecular evolution of 11 osmoregulation-related genes in 11 cetacean species, which represented all of the major cetacean clades. The results demonstrated positive selection acting on angiotensin converting enzyme (ACE), angiotensinogen (AGT), SLC14A2, and aquaporin 2 (AQP2). This evidence for the positive selection of AQP2 and SLC14A2 suggests that the adaptive evolution of these genes has helped to enhance the capacity for water and urea transport, thereby leading to the concentration of urine, which is an efficient mechanism for maintaining the water balance. By contrast, a series of positively selected amino acid residues identified in the ACE and AGT (two key members of the renin-angiotensin-aldosterone system, RAAS) proteins of cetaceans suggests that RAAS might have been adapted to maintain the water and salt balance in response to a hyperosmotic environment. Radical amino acid changes in positively selected sites were distributed among most internal and terminal branches of the cetacean phylogeny, which suggests the pervasively adaptive evolution of osmoregulation since the origin of cetaceans and their subsequent diversification.

Conclusions

This is the first comprehensive analysis of the molecular evolution of osmoregulation-related genes in cetaceans in response to selection pressure from a generally hyperosmotic environment. Four genes, i.e., AQP2, SLC14A2, ACE, and AGT were subject to positive selection in cetaceans, which suggests that cetaceans may have adapted to maintain their water and salt balance. This also suggests that cetaceans may have evolved an effective and complex mechanism for osmoregulation.

Poloxamer-188 attenuates TBI-induced blood-brain barrier damage leading to decreased brain edema and reduced cellular death

Plasmalemma permeability plays an important role in the secondary neuronal death induced by traumatic brain injury (TBI). Previous works showed that Poloxamer 188 (P188) could restore the intactness of the plasma membrane and play a cytoprotective action. However, the roles of P188 in blood-brain barrier (BBB) integrity and TBI-induced neural cell death are still not clear. In this study, mice were induced TBI by controlled cortical impact (CCI), and cerebral water content was measured to explore the profile of brain edema after CCI. Further, the regimen of P188 in mouse CCI models was optimized. The neurological test and BBB integrity assessment were performed, and the numbers of TBI-induced neural cell death were counted by propidium iodide (PI) labeling. The expression of apoptotic pathway associated proteins (Bax, cyt-c, caspase-8, caspase-9, caspase-3, P53) and aquaporin-4 (AQP4) was assessed by RT-PCR or immunoblotting. The data showed that the brain edema peaked at 24 h after TBI in untreated animals. Tail intravenous injection of P188 (4 mg/ml, 100 μl) 30 min before TBI or within 30 min after TBI could attenuate TBI-induced brain edema. P188 pre-treatment restored BBB integrity, suppressed TBI-induced neural cell death, and improved neurological function. TBI induced an up-regulation of Bax, cyt-c, caspase-8, caspase-9, caspase-3, and the expression of p53 was down-regulated by P188 pre-treatment. AQP4 mainly located on endothelial cells and astrocytes, and its expression was also regulated by P188 pretreatment. All these results revealed that P188 attenuates TBI-induced brain edema by resealing BBB and regulating AQP4 expression, and suppressed apoptosis through extrinsic or intrinsic pathway. Plasmalemma permeability may be a potential target for TBI treatment.

Accumulating evidence supports a taste component for free fatty acids in humans

The requisite criteria for what constitutes a taste primary have not been established. Recent advances in understanding of the mechanisms and functions of taste have prompted suggestions for an expanded list of unique taste sensations, including fat, or more specifically, free fatty acids (FFA). A set of criteria are proposed here and the data related to FFA are reviewed on each point. It is concluded that the data are moderate to strong that there are: A) adaptive advantages to FFA detection in the oral cavity; B) adequate concentrations of FFA to serve as taste stimuli; C) multiple complimentary putative FFA receptors on taste cells; D) signals generated by FFA that are conveyed by gustatory nerves; E) sensations generated by FFA that can be detected and scaled by psychophysical methods in humans when non-gustatory cues are masked; and F) physiological responses to oral fat/FFA exposure. On no point is there strong evidence challenging these observations. The reviewed findings are suggestive, albeit not definitive, that there is a taste component for FFA.

Hyponatremia and the syndrome of inappropriate secretion of antidiuretic hormone (SIADH)

The syndrome of inappropriate ADH secretion (SIADH), also recently referred to as the "syndrome of inappropriate antidiuresis", is an often underdiagnosed cause of hypotonic hyponatremia, resulting for instance from ectopic release of ADH in lung cancer or as a side-effect of various drugs. In SIADH, hyponatremia results from a pure disorder of water handling by the kidney, whereas external Na+ balance is usually well regulated. Despite increased total body water, only minor changes of urine output and modest edema are usually seen. Renal function and acid-base balance are often preserved, while neurological impairment may range from subclinical to life-threatening. Hypouricemia is a distinguishing feature. The major causes and clinical variants of SIADH are reviewed, with particular emphasis on iatrogenic complications and hospital-acquired hyponatremia. Effective treatment of SIADH with water restriction, aquaretics, or hypertonic saline + loop diuretics, as opposed to worsening of hyponatremia during parenteral isotonic fluid administration, underscores the importance of an early accurate diagnosis and careful follow-up of these patients.

Selective covalent labeling of tag-fused GPCR proteins on live cell surface with a synthetic probe for their functional analysis

Selective protein labeling with a small molecular probe is a versatile method for elucidating protein functions in living cells. In this paper, we report a covalent labeling method of tag-fused G-protein coupled receptor (GPCR) proteins expressing on cell surfaces utilizing small functional molecules. This method employs the selective and rapid reaction of a peptide tag and a molecular probe, which comprises the cysteine-containing short CA6D4x2 tag (CAAAAAADDDDGDDDD) and a tetranuclear Zn(II)-DpaTyr probe containing a reactive alpha-chloroacetyl moiety. The covalent labeling of tag-fused GPCRs such as bradykinin receptor (B2R) and acetylcholine receptor (m1AchR) selectively proceeded under physiological conditions during short incubation (10-30 min) with Zn(II)-DpaTyr probes bearing various functional groups. Labeling with fluorophore-appended Zn(II)-DpaTyr probes enabled visualization of the GPCRs on the surface of HEK293 cells by fluorescence. Labeling with the biotin-appended probe allowed introduction of a biotin unit into the GPCRs. This biotin label was utilized for fluorescence bioimaging studies and postlabeling blotting analysis of the labeled GPCRs by use of the specific biotin-streptavidin interaction. The utility of this labeling method was demonstrated in several function analyses of GPCRs, such as fluorescence visualization of the stimuli-responsive internalization of GPCRs and pH change in endosomes containing the internalized GPCRs.

Oral thresholds and suprathreshold intensity ratings for free fatty acids on 3 tongue sites in humans: implications for transduction mechanisms

Multiple putative free fatty acid (FFA) transduction mechanisms have been identified in the oral cavity. They reportedly differ in their distribution on the tongue and each has a unique range of ligand specificities. This suggests that there should be regional differences in sensory responses to varying FFAs. This was assessed through spatial testing with caproic (C), lauric (L), and stearic (S) FFAs among 35 healthy adults. Stimuli were applied to the fungiform (FU), foliate (FO), and circumvallate (CV) papillae with a cotton-tipped applicator. Oral detection thresholds were measured by an ascending, 3-alternative, forced-choice, sip and spit procedure. Intensity ratings were obtained on the general labeled magnitude scale. Nongustatory cues were minimized by testing with the nares blocked, eyes covered, and by masking tactile cues with the addition of gum acacia and mineral oil to the stimuli vehicle. Thresholds were obtained from nearly all individuals at each site, and the concentration was similar across the 3 FFAs. Absolute intensity ratings differed significantly with C > L > S overall and at the CV and FO papillae. At the FU papillae, the L and S ratings were comparable. Ratings were highest at the FU followed by the CV and then the FO papillae. Slopes of the concentration-intensity rating functions were higher for L compared with C and S at the CV papillae as well as both L and C compared with S at the FO papillae. However, overall, slopes were comparable across sites. These findings strengthen evidence for oral FFA perception in humans by replicating threshold sensitivity findings and documenting monotonic scaling ability for these stimuli. Further, they challenge current views on transduction as sensory responsiveness was observed at tongue sites not predicted to support FFA detection.

Oligomeric structure of colicin ia channel in lipid bilayer membranes

Colicin Ia is a soluble, harpoon-shaped bacteriocin which translocates across the periplasmic space of sensitive Escherichia coli cell by parasitizing an outer membrane receptor and forms voltage-gated ion channels in the inner membrane. This process leads to cell death, which has been thought to be caused by a single colicin Ia molecule. To directly visualize the three-dimensional structure of the channel, we generated two-dimensional crystals of colicin Ia inserted in lipid-bilayer membranes and determined a approximately 17 three-dimensional model by electron crystallography. Supported by velocity sedimentation, chemical cross-linking and single-particle image analysis, the three-dimensional structure is a crown-shaped oligomer enclosing a approximately 35 A-wide extrabilayer vestibule. Our study suggests that lipid insertion instigates a global conformational change in colicin Ia and that more than one molecule participates in the channel architecture with the vestibule, possibly facilitating the known large scale peptide translocation upon channel opening.

Is there a fatty acid taste?

Taste is a chemical sense that aids in the detection of nutrients and guides food choice. A limited number of primary qualities comprise taste. Accumulating evidence has raised a question about whether fat should be among them. Most evidence indicates triacylglycerol is not an effective taste stimulus, though it clearly contributes sensory properties to foods by carrying flavor compounds and altering texture. However, there is increasing anatomical, electrophysiological, animal behavior, imaging, metabolic, and psychophysical evidence that free fatty acids are detectable when non-taste cues are minimized. Free fatty acids varying in saturation and chain length are detectable, suggesting the presence of multiple transduction mechanisms and/or a nonspecific mechanism in the oral cavity. However, confirmation of "fatty" as a taste primary will require additional studies that verify these observations are taste specific. Oral exposure to free fatty acids likely serves as a warning signal to discourage intake and influences lipid metabolism.

Oral detection of short-, medium-, and long-chain free fatty acids in humans

There is increasing evidence supporting an oral chemosensory detection system for free fatty acids (FFA). The presumptive transduction mechanisms have different ligand specificities. Psychophysical studies with FFA varying in chain length and saturation may aid in identifying the presence and functionality of these mechanisms in humans. Oral detection thresholds were measured for linoleic, stearic, lauric, and caproic acids in 32 healthy adults by an ascending, 3-alternative, forced-choice, sip and spit procedure. Thresholds were obtained for all fatty acids from all participants, but the distributions were wide and nonnormal. Thresholds were not correlated between fatty acids nor with thresholds for sucrose (taste), butanol (olfactory), mineral oil, or gum acacia (both somatosensory). These data demonstrate human oral sensitivity to short-, medium-, and long-chain FFA and suggest the presence of multiple transduction mechanisms. The findings are consistent with, but do not definitively demonstrate, a role for taste that may have a genetic basis.

From membrane pores to aquaporins: 50 years measuring water fluxes

This review focuses on studies of water movement across biological membranes performed over the last 50 years. Different scientific approaches had tried to elucidate such intriguing mechanism, from hypotheses emphasizing the role of the lipid bilayer to the cloning of aquaporins, the ubiquitous proteins described as specific water channels. Pioneering and clarifying biophysical work are reviewed beside results obtained with the help of recent sophisticated techniques, to conclude that great advances in the subject live together with old questions without definitive answers.

Aquaporins--new players in cancer biology

The aquaporins (AQPs) are small, integral-membrane proteins that selectively transport water across cell plasma membranes. A subset of AQPs, the aquaglyceroporins, also transport glycerol. AQPs are strongly expressed in tumor cells of different origins, particularly aggressive tumors. Recent discoveries of AQP involvement in cell migration and proliferation suggest that AQPs play key roles in tumor biology. AQP1 is ubiquitously expressed in tumor vascular endothelium, and AQP1-null mice show defective tumor angiogenesis resulting from impaired endothelial cell migration. AQP-expressing cancer cells show enhanced migration in vitro and greater local tumor invasion, tumor cell extravasation, and metastases in vivo. AQP-dependent cell migration may involve AQP-facilitated water influx into lamellipodia at the front edge of migrating cells. The aquaglyceroporin AQP3, which is found in normal epidermis and becomes upregulated in basal cell carcinoma, facilitates cell proliferation in different cell types. Remarkably, AQP3-null mice are resistant to skin tumorigenesis by a mechanism that may involve reduced tumor cell glycerol metabolism and ATP generation. Together, the data suggest that AQP expression in tumor cells and tumor vessels facilitates tumor growth and spread, suggesting AQP inhibition as a novel antitumor therapy.

Urine concentration and avian aquaporin water channels

Although birds and mammals have evolved from primitive tetrapods and advanced divergently, both can conserve water by producing hyperosmotic urine. Unique aspects in the avian system include the presence of loopless and looped nephrons, lack of the thin ascending limb of Henle's loop, a corticomedullary osmotic gradient primarily consisting of NaCl without contribution of urea, and significant postrenal modification of final urine. The countercurrent multiplier mechanism operates between the descending and ascending limbs of Henle via recycling of a single solute (NaCl) with no water accompaniment, forming an osmotic gradient along the medullary cone. Bird kidneys and developing rat kidneys share morphological and functional characteristics. Avian kidneys express aquaporin (AQP) 1, 2, and 4 homologues that share considerable homology with mammalian counterparts, but their distribution and function may not be the same. AQP2 expression in Japanese quail (q) evolves in the collecting duct of early metanephric kidneys and continues to increase in intensity and distribution during nephrogenesis and maturation. qAQP2 mRNA and protein are increased by arginine vasotocin (avian ADH), but vasotocin-induced enhancement of cAMP production and water permeability are less marked than in mammalian kidneys. Nephrogenesis is delayed by insufficient nutrition in avian embryos and newborns and results in fewer nephrons and an impaired water balance in adults. Diabetes insipidus quail with homozygous autosomal recessive mutation and an unaffected vasotocin system have low AQP2 expression, underdeveloped medullary cones. Comparative studies will provide important insight into integrative, cellular, and molecular mechanisms of epithelial water transport and its control by humoral, neural, and hemodynamic mechanisms.

The taste transduction channel TRPM5 is a locus for bitter-sweet taste interactions

Ordinary gustatory experiences, which are usually evoked by taste mixtures, are determined by multiple interactions between different taste stimuli. The most studied model for these gustatory interactions is the suppression of the responses to sweeteners by the prototype bitter compound quinine. Here we report that TRPM5, a cation channel involved in sweet taste transduction, is inhibited by quinine (EC(50)=50 microM at -50 mV) owing to a decrease in the maximal whole-cell TRPM5 conductance and an acceleration of channel closure. Notably, quinine inhibits the gustatory responses of sweet-sensitive gustatory nerves in wild-type (EC(50)= approximately 1.6 mM) but not in Trpm5 knockout mice. Quinine induces a dose- and time-dependent inhibition of TRPM5-dependent responses of single sweet-sensitive fibers to sucrose, according to the restricted diffusion of the drug into the taste tissue. Quinidine, the stereoisomer of quinine, has similar effects on TRPM5 currents and on sweet-induced gustatory responses. In contrast, the chemically unrelated bitter compound denatonium benzoate has an approximately 100-fold weaker effect on TRPM5 currents and, accordingly, at 10 mM it does not alter gustatory responses to sucrose. The inhibition of TRPM5 by bitter compounds constitutes the molecular basis of a novel mechanism of taste interactions, whereby the bitter tastant inhibits directly the sweet transduction pathway.

Regulation of root nitrate uptake at the NRT2.1 protein level in Arabidopsis thaliana

In Arabidopsis the NRT2.1 gene encodes a main component of the root high-affinity nitrate uptake system (HATS). Its regulation has been thoroughly studied showing a strong correlation between NRT2.1 expression and HATS activity. Despite its central role in plant nutrition, nothing is known concerning localization and regulation of NRT2.1 at the protein level. By combining a green fluorescent protein fusion strategy and an immunological approach, we show that NRT2.1 is mainly localized in the plasma membrane of root cortical and epidermal cells, and that several forms of the protein seems to co-exist in cell membranes (the monomer and at least one higher molecular weight complex). The monomer is the most abundant form of NRT2.1, and seems to be the one involved in NO(3)(-) transport. It strictly requires the NAR2.1 protein to be expressed and addressed at the plasma membrane. No rapid changes in NRT2.1 abundance were observed in response to light, sucrose, or nitrogen treatments that strongly affect both NRT2.1 mRNA level and HATS activity. This suggests the occurrence of post-translational regulatory mechanisms. One such mechanism could correspond to the cleavage of NRT2.1 C terminus, which results in the presence of both intact and truncated proteins in the plasma membrane.

Equine sweating and anhidrosis Part 2: anhidrosis

The condition of anhidrosis is described in this review, and the latest theories on the causal factors are explored. The evidence supports the hypothesis that anhidrosis is an inappropriate response to prolonged climatic stress (generally combined heat and high humidity), which can be evoked in a small (approximately 10 +/- 5%) proportion of the equine population. It is caused by gradual failure of the glandular secretory cell processes, initiated by desensitization and subsequent down-regulation of the cell receptors as a result of continued adrenaline-driven hyperactivity. It progresses through secretory failure and culminates in gradual, probably irreversible, glandular dedifferentiation and ultimate degeneration. There is a need for considerably more research on the secretory and transcriptional processes to document the changes arising within the glandular secretory mechanism as a prelude to development of a corrective treatment.

Tissue distribution, effects of salinity acclimation, and ontogeny of aquaporin 3 in the marine teleost, silver sea bream (Sparus sarba)

The purpose of the present study was to ascertain the tissue-specific expression of the water channel protein, aquaporin 3 (AQP3), during salinity acclimation and larval development of silver sea bream (Sparus sarba). A cDNA fragment encoding aquaporin 3 (aqp3) from silver sea bream gill was cloned and from the deduced amino acid sequence a polyclonal antibody was prepared. AQP3 was found to be present in gill, kidney, liver, brain, heart, and spleen but not in whole blood. The abundance of AQP3 was significantly highest in gills of hypoosmotic (6 ppt) and isoosmotic (12 ppt) acclimated sea bream when compared to seawater (33 ppt) and hypersaline (50 ppt)- acclimated sea bream. Spleen tissue also displayed significantly high levels of AQP3 protein in hypoosmotic and isoosmotic salinities whereas the AQP3 abundance in brain, liver, heart, and kidney remained unchanged across the range of salinities tested. The ontogenetic profile of AQP3 was also investigated from developing sea bream larvae and AQP3 was first detected at 14 days posthatch (dph) and increased steadily up to 28-46 dph. In conclusion, this study has demonstrated that AQP3 expression is modulated in gill and spleen tissue of salinity acclimated sea bream and that it can be detected relatively early during larval development.

AQPs and control of vesicle volume in secretory cells

Aquaporins (AQPs) are a family of small, hydrophobic, integral membrane proteins. In mammals, they are expressed in many epithelia and endothelia and function as channels that permit water or small solutes to pass. Although the AQPs reside constitutively at the plasma membrane in most cell types, the presence of AQPs in intracellular organelles such as secretory granules and vesicles has currently been demonstrated. The secretory granules and vesicles contain secretory proteins, migrate to particular locations within the cell close to the plasma membrane and release their contents to the outside. During the process, including exocytosis, regulation of secretory granule or vesicle volume is important. This paper reviews the possible role of AQPs in secretory granules and vesicles.

Estrogen-induced proliferation of uterine epithelial cells is independent of estrogen receptor alpha binding to classical estrogen response elements

Acting via the estrogen receptor (ER), estradiol exerts pleomorphic effects on the uterus, producing cyclical waves of cellular proliferation and differentiation in preparation for embryo implantation. In the classical pathway, the ER binds directly to an estrogen response element to activate or repress gene expression. However, emerging evidence supports the existence of nonclassical pathways in which the activated ER alters gene expression through protein-protein tethering with transcription factors such as c-Fos/c-Jun B (AP-1) and Sp1. In this report, we examined the relative roles of classical and nonclassical ER signaling in vivo by comparing the estrogen-dependent uterine response in mice that express wild-type ERalpha, a mutant ERalpha (E207A/G208A) that selectively lacks ERE binding, or ERalpha null. In the compound heterozygote (AA/-) female, the nonclassical allele (AA) was insufficient to mediate an acute uterotrophic response to 17beta-estradiol (E2). The uterine epithelial proliferative response to E2 and 4-hydroxytamoxifen was retained in the AA/-females, and uterine luminal epithelial height increased commensurate with the extent of ERalpha signaling. This proliferative response was confirmed by 5-bromo-2'-deoxyuridine incorporation. Microarray experiments identified cyclin-dependent kinase inhibitor 1A as a nonclassical pathway-responsive gene, and transient expression experiments using the cyclin-dependent kinase inhibitor 1A promoter confirmed transcriptional responses to the ERalpha (E207A/G208A) mutant. These results indicate that nonclassical ERalpha signaling is sufficient to restore luminal epithelial proliferation but not other estrogen-responsive events, such as fluid accumulation and hyperemia. We conclude that nonclassical pathway signaling via ERalpha plays a critical physiologic role in the uterine response to estrogen.

Electromechanical models of the outer hair cell composite membrane

The outer hair cell (OHC) is an extremely specialized cell and its proper functioning is essential for normal mammalian hearing. This article reviews recent developments in theoretical modeling that have increased our knowledge of the operation of this fascinating cell. The earliest models aimed at capturing experimental observations on voltage-induced cellular length changes and capacitance were based on isotropic elasticity and a two-state Boltzmann function. Recent advances in modeling based on the thermodynamics of orthotropic electroelastic materials better capture the cell's voltage-dependent stiffness, capacitance, interaction with its environment and ability to generate force at high frequencies. While complete models are crucial, simpler continuum models can be derived that retain fidelity over small changes in transmembrane voltage and strains occurring in vivo. By its function in the cochlea, the OHC behaves like a piezoelectric-like actuator, and the main cellular features can be described by piezoelectric models. However, a finer characterization of the cell's composite wall requires understanding the local mechanical and electrical fields. One of the key questions is the relative contribution of the in-plane and bending modes of electromechanical strains and forces (moments). The latter mode is associated with the flexoelectric effect in curved membranes. New data, including a novel experiment with tethers pulled from the cell membrane, can help in estimating the role of different modes of electromechanical coupling. Despite considerable progress, many problems still confound modelers. Thus, this article will conclude with a discussion of unanswered questions and highlight directions for future research.

Immunolocalization of aquaporin-5 expression in sweat gland cells from normal and anhidrotic horses

Western blot analysis showed that sweat gland cells from freely sweating horses expressed the water channel aquaporin-5 (AQP-5). Immunohistochemistry revealed a strong AQP-5-like activity reaction at the apical membrane of the glandular secretory cells, which was absent from the surrounding myoepithelium and all other skin structures. In anhidrotic horses, AQP-5 was also found at the apical membrane of the luminal sweat gland cells, but the level of expression reduced with the length of time that the animal had displayed anhidrosis. The level of AQP-5 expression was substantially reduced in animals with long-term anhidrosis, hence implicating water channel impairment as a possible factor in the development of this disorder.

Nephrogenic diabetes insipidus in mice lacking all nitric oxide synthase isoforms

Nitric oxide (NO) is produced in almost all tissues and organs, exerting a variety of biological actions under physiological and pathological conditions. NO is synthesized by three different isoforms of NO synthase (NOS), including neuronal, inducible, and endothelial NOSs. Because there are substantial compensatory interactions among the NOS isoforms, the ultimate roles of endogenous NO in our body still remain to be fully elucidated. Here, we have successfully developed mice in which all three NOS genes are completely deleted by crossbreeding singly NOS-/- mice. NOS expression and activities were totally absent in the triply NOS-/- mice before and after treatment with lipopolysaccharide. Although the triply NOS-/- mice were viable and appeared normal, their survival and fertility rates were markedly reduced as compared with the wild-type mice. Furthermore, these mice exhibited marked hypotonic polyuria, polydipsia, and renal unresponsiveness to an antidiuretic hormone, vasopressin, all of which are characteristics consistent with nephrogenic diabetes insipidus. In the kidney of the triply NOS-/- mice, vasopressin-induced cAMP production and membranous aquaporin-2 water channel expression were reduced associated with tubuloglomerular lesion formation. These results provide evidence that the NOS system plays a critical role in maintaining homeostasis, especially in the kidney.

Localized glucose and water influx facilitates Cryptosporidium parvum cellular invasion by means of modulation of host-cell membrane protrusion

Dynamic membrane protrusions such as lamellipodia and filopodia are driven by actin polymerization and often hijacked by intracellular microbes to enter host cells. The overall rate of membrane protrusion depends on the actin polymerization rate and the increase of localized cell volume. Although the signaling pathways involving actin polymerization are well characterized, the molecular mechanisms regulating local cell volume associated with membrane protrusion are unclear. Cryptosporidium parvum, an intracellular parasite, depends on host-cell membrane protrusion to accomplish cell entry and form the parasitophorous vacuole. Here, we report that C. parvum infection of cholangiocytes recruits host-cell SGLT1, a Na+/glucose cotransporter, and aquaporin 1 (AQP1), a water channel, to the attachment site. SGLT1-dependent glucose uptake occurs at the attachment site. Concordantly, the region of attachment displays localized water influx that is inhibited by either suppression of AQP1 by means of AQP1-small interfering RNA (siRNA) or inhibition of SGLT1 by a specific pharmacologic inhibitor, phlorizin. Inhibition of SGLT1 does not affect actin accumulation but decreases the membrane protrusion at the attachment site. Moreover, functional inhibition of host-cell AQP1 and SGLT1 hampers C. parvum invasion of cholangiocytes. Thus, glucose-driven, AQP-mediated localized water influx is involved in the membrane protrusion during C. parvum cellular invasion, phenomena that may also be relevant to the mechanisms of cell membrane protrusion in general.

Involvement of Aquaporin-5 Water Channel in Osmoregulation in Parotid Secretory Granules

Aquaporins (AQPs) are a family of channel proteins that allow water or very small solutes to pass, functioning in tissues where the rapid and regulated transport of fluid is necessary, such as the kidney, lung, and salivary glands. Aquaporin-5 (AQP5) has been demonstrated to localize on the luminal surface of the acinar cells of the salivary glands. In this paper, we investigated the expression and function of AQP5 in the secretory granules of the rat parotid gland. AQP5 was detected in the secretory granule membranes by immunoblot analysis. The immunoelectron microscopy experiments confirmed that AQP5 was to be found in the secretory granule membrane. Anti-AQP5 antibody evoked lysis of the secretory granules but anti-aquaporin-1 antibody did not and AQP1 was not detected in the secretory granule membranes by immunoblot analysis. When chloride ions were removed from the solution prepared for suspending secretory granules, the granule lysis induced by anti-AQP5 antibody was inhibited. Furthermore, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, an anion channel blocker, blocked the anti-AQP5 antibody-induced secretory granule lysis. These results suggest that AQP5 is, expressed in the parotid gland secretory granule membrane and is involved in osmoregulation in the secretory granules.

Gene expression profiles in rat intestine identify pathways for 1,25-dihydroxyvitamin D(3) stimulated calcium absorption and clarify its immunomodulatory properties

Microarray technology has been used to discover 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) induced gene expression changes in rat small intestine in vivo. Here, we report gene expression changes related to intestinal absorption or transport, the immune system and angiogenesis in response to 1,25-(OH)(2)D(3). Vitamin D deficient rats were intrajugularly given vehicle or vehicle containing 730 ng of 1,25-(OH)(2)D(3)/kg of body weight. Intestinal mRNA was harvested from duodenal mucosa at 15 min, 1, 3, and 6 h post-injection and studied by Affymetrix microarrays. Genes significantly affected by 1,25-(OH)(2)D(3) were confirmed by quantitative RT-PCR with remarkable agreement. The most strongly affected gene in intestine was CYP24 with 97-fold increase at 6 h post-1,25-(OH)(2)D(3) treatment. Intestinal calcium absorption genes: TRPV5, TRPV6, calbindin D(9k), and Ca(2+) dependent ATPase all were up-regulated in response to 1,25-(OH)(2)D(3), supporting the currently accepted mechanism of 1,25-(OH)(2)D(3) induced transcellular calcium transport. However, a 1,25-(OH)(2)D(3) suppression of several intra-/intercellular matrix modeling proteins such as sodium/potassium ATPase, claudin 3, aquaporin 8, cadherin 17, and RhoA suggests a vitamin D regulation of tight junction permeability and paracellular calcium transport. Several other genes related to the immune system and angiogenesis whose expression was changed in response to 1,25-(OH)(2)D(3) provided evidence for an immunomodulatory and anti-angiogenic role of 1,25-(OH)(2)D(3).

Pathomechanisms of Cystoid Macular Edema

Cystoid macular edema (CME) is a well-known endpoint of various ocular diseases, but the relative pathogenic impact of extra- and intracellular fluid accumulation within the retinal tissue still remains uncertain. While most authors favor an extracellular fluid accumulation as the main causative factor of cyst formation, there are indications that Müller cell swelling may also contribute to CME development (particularly in cases without significant angiographic vascular leakage). Vascular leakage occurs after a breakdown of the blood-retinal barrier during traumatic, vascular, and inflammatory ocular diseases, and allows the serum to get into the retinal interstitium. Since intraretinal fluid distribution is restricted by two diffusion barriers, the inner and outer plexiform layers, serum leakage from intraretinal vessels causes cysts mainly in the inner nuclear layer while leakage from choroid/pigment epithelium generates (in addition to subretinal fluid accumulation) cyst formation in the Henle fiber layer. In the normal healthy retina, the transretinal water fluxes are mediated by glial and pigment epithelial cells. These water fluxes are inevitably coupled to fluxes of osmolytes; in the case of glial (Müller) cells, to K(+) clearance currents. For this purpose, the cells express a complex, microtopographically optimized pattern of transporters and channels for osmolytes and water in their plasma membrane. Ischemic/hypoxic alterations of the retinal microvasculature result in gliotic responses which involve down-regulation of K(+) channels in the perivascular Müller cell end-feet. This means a closure of the main pathway which normally generates the osmotic drive for the redistribution of water from the inner retina into the blood. The result is an intracellular K(+) accumulation which, then, osmotically drives water from the blood into the glial cells (i.e., in the opposite direction) and causes glial cell swelling, edema, and cyst formation. While the underlying mechanisms await further research, it is expected that their improved knowledge will stimulate the development of novel therapeutic approaches to resolve edema in retinal tissue.

Saccharin stimulates the "deterrent" cell in the blowfly: behavioral and electrophysiological evidence

In the attempt to gain more information on the mechanisms underlying bitter and/or sweet taste reception, we have investigated the responses of labellar chemosensilla in the blowfly Protophormia terraenovae to Na-saccharin, as compared to sweet stimuli (sucrose or fructose) and bitter stimuli (denatonium benzoate or amiloride). Electrophysiological and behavioral results indicate that the sweetener Na-saccharin inhibits the "sugar" cell in the labellar taste sensilla of the blowfly P. terraenovae. In multichoice preference tests, flies ingested more of the solutions containing sugar to those with sugar+Na-saccharin. This finding is in good agreement with the spike frequency reduction observed for the "sugar" cell activity. Analysis of the spike discharges also shows a positive dose-response for the "deterrent" cell following stimulation with Na-saccharin and denatonium benzoate. Flies drank any of the Na-saccharin solutions, regardless of their concentration, less than water, thus indicating a weak deterring effect on water drinking. The prevailing activation of the "deterrent" cell by stimulation with Na-saccharin is not directly coupled with a coherent behavioral output. Cross adaptation was found to occur between responses to Na-saccharin and denatonium benzoate or amiloride regardless of the order of adapting stimuli. In the case of sweet stimuli, cross adaptation occurred when the adapting stimulus was Na-saccharin, but it did not when the adapting stimuli were sucrose or fructose. Addition of Na-saccharin to both sugars significantly depressed the spike firing frequency, while an increase was observed with denatonium benzoate or amiloride.

Aquaporin-1, nothing but a water channel

Aquaporin-1 (AQP1) is a membrane channel that allows rapid water movement driven by a transmembrane osmotic gradient. It was claimed to have a secondary function as a cyclic nucleotide-gated ion channel. However, upon reconstitution into planar bilayers, the ion channel exhibited a 10-fold lower single channel conductance than in Xenopus oocytes and a 100-fold lower open probability (<10(-6)) of doubtful physiological significance (Saparov, S. M., Kozono, D., Rothe, U., Agre, P., and Pohl, P. (2001) J. Biol. Chem. 276, 31515-31520). Investigating AQP1 expressed in human embryonic kidney cells, we now have shown that the discrepancy is not due to alterations of AQP1 properties upon reconstitution into bilayers but rather to regulatory processes of the oocyte expression system that may have been misinterpreted as AQP1 ion channel activity. As confirmed by laser scanning reflection microscopy, from 0.8 to 1.4 x 10(6) AQP1 copies/cell contributed to osmotic cell swelling. The proper plasma membrane localization was confirmed by observing the fluorescence of the N-terminal yellow fluorescent protein tag. Whole-cell patch clamp experiments of wild type or tagged AQP1-expressing cells revealed that neither cGMP nor cAMP mediated ion channel activity. The lack of significant CNG ion channel activity rules out a secondary role of AQP1 water channels in cellular signal transduction.

Effect of dDAVP on basolateral cell surface water permeability in the outer medullary collecting duct

We report a novel approach for assessing the volume of living cells which allows quantitative, high-resolution characterization of dynamic changes in cell volume while retaining the cell functionality. The aim of this study was to evaluate the short-term effect of vasopressin on basolateral cell surface water permeability in the outer medullary collecting duct (OMCD). The permeability of the basolateral cell membrane was determined in the tubules where the apical membrane was blocked with oil injected into the lumen. The apparent coefficient of water permeability (Pf) was evaluated by measuring the cell swelling after the step from hypertonic to isotonic medium (600 mosm to 300 mosm). Desmopressin (dDAVP) induced an increase of the basolateral Pf from 113.7+/-8.5 microm/s in control cells to 186.6+/-11.4 mum/s in micro-dissected fragments of the OMCD incubated in vitro (10(-7) M dDAVP, 30 min at 37 degrees C) (P<0.05). Mercury caused pronounced inhibition of basolateral water permeability (26.0+/-6.9 microm/s; P<0.05). The effect of mercury (1.0 mM HgCl2) was reversible: after washing the fragments with PBS for 20 min, Pf values were restored to the control levels (125.0+/-9.5 microm/s). The results of the study indicate the existence of a mechanism controlling the osmotic water permeability of the basolateral cell membrane in the OMCD epithelium.

Expression and localization of aquaporins, members of the water channel family, during development of the rat submandibular gland

The expression and localization of aquaporins (AQP1-AQP5), members of the water channel family, in the developing rat submandibular gland were analysed using RT-PCR, Northern blotting and immunohistochemistry to explore their relation to the development of this salivary gland. RT-PCR analysis revealed unique expression patterns of each AQP. AQP1 was expressed constitutively during prenatal development, whereas the expression of AQP5 became more intense in the course of development from embryonic day 16.5 (E16) to E20. These expression patterns concurred with the results of Northern blot analysis. AQP3 and AQP4 mRNAs in the prenatal development were not detected in Northern blots, although they were detected by RT-PCR. During postnatal development, AQP5 and AQP1 mRNAs were expressed continuously, but no message for AQP3 or AQP4 was detected. AQP2 mRNA was not detected during either prenatal or postnatal development in this tissue. Immunohistochemical studies revealed that AQP5 was first localized at the apical membrane of proacinar cells at E18, and then became clearly distributed at the apical membrane of acinar cells in accordance with the differentiation and establishment of the mature acini. In addition, some vasculature also showed immunoreactivity for AQP5. AQP1 was immunolocalized in the blood vessels, including capillaries, of the gland throughout development. These observations suggest the existence of transcriptional regulation of rat AQP5, which is one of the most probable regulators of saliva production and secretion, during the establishment of the functional submandibular salivary gland.

Proteotyping of mammary tissue from transgenic and gene knockout mice with immunohistochemical markers: a tool to define developmental lesions

Through the use of transgenic and gene knockout mice, several studies have identified specific genes required for the functional development of mammary epithelium. Although histological and milk protein gene analyses can provide useful information regarding functional differentiation, they are limited in their ability to precisely define the molecular lesions. For example, mice that carry a mutation in one of the subunits of the IkappaB kinase, IKKalpha, cannot lactate despite the presence of histologically normal alveolar compartment and the expression of milk protein genes. To further define and understand such lesions on a molecular level, we sought evidence for proteins that are differentially expressed during mammary gland development with a view to generating a tissue proteotype. Using database screens and immunohistochemical analyses, we have identified three proteins that exhibit distinct profiles. Here, using mouse models as test biological systems, we demonstrate the development and application of mammary tissue proteotyping and its use in the elucidation of specific developmental lesions. We propose that the technique of proteotyping will have wide applications in the analyses of defects in other mouse models.

Mosquito (Aedes aegypti ) aquaporin, present in tracheolar cells, transports water, not glycerol, and forms orthogonal arrays in Xenopus oocyte membranes

Previous results showed that mRNA encoding a putative aquaporin (AQP) (GenBank accession number AF218314) is present in the tracheolar cells associated with female Aedes aegypti Malpighian tubules. In this study, immunohistochemistry detected the protein, AeaAQP, also in tracheolar cells, suggesting its involvement in water movement in the respiratory system. When expressed in Xenopus oocytes, AeaAQP increased the osmotic water permeability from 15 x 10(-6) to 150 x 10(-6) m x s-1, which was inhibited by mercury ions. No permeability to glycerol or other solute was observed. AeaAQP expressed in oocytes was solubilized as a homotetramer in nondenaturing detergent as deduced from velocity centrifugation on density gradients. Phylogenetic analysis of MIP (major intrinsic protein) family sequences shows that AeaAQP clusters with other native orthogonal array forming proteins. Specific orthogonal arrays were detected by freeze-fracture analysis of AeaAQP oocyte membranes. We conclude that, in tracheolar cells of A. aegypti, AeaAQP is probably a highly water-permeable homotetrameric MIP which natively can form 2D crystals.

AQP3 deficiency in humans and the molecular basis of a novel blood group system, GIL

AQP3 is a water and glycerol channel present on human erythrocytes and in various tissues. By protein and molecular biology analysis, two unrelated probands who developed alloantibodies to the high frequency antigen GIL were found to be AQP3-deficient. The defect is caused by homozygous mutation affecting the 5' donor splice site of intron 5 of the AQP3 gene. This mutation causes the skipping of exon 5 and generates a frameshift and premature stop codon. Functional studies by 90 degrees light scattering using a stopped-flow spectrometer revealed the absence of facilitated glycerol transport across red cell membranes from the probands, but the water and urea transports were normal. Expression studies into COS-7 cells followed by flow cytometry analysis showed that only cells transfected with AQP3 cDNA strongly reacted with anti-GIL antibodies. These findings represent the first reported cases of AQP3 deficiency in humans and provide the molecular basis of a new blood group system, GIL, encoded by the AQP3 protein.

Tissue distribution and membrane localization of aquaporin-9 water channel: evidence for sex-linked differences in liver

Aquaporin-9 (AQP9) is a water channel membrane protein also permeable to small solutes such as urea, glycerol, and 5-fluorouracil, a chemotherapeutic agent. With the aim of understanding the pathophysiological role of AQP9, we performed an extensive analysis by Western blotting, RT-PCR, and immunolocalization in rat tissues. Western blotting analysis revealed a major band of approximately 32 kD in testis, liver, and brain. Immunofluorescence showed strong expression of AQP9 in the plasma membrane of testis Leydig cells. In liver, AQP9 expression was found to be sex-linked. Male rats had higher levels of AQP9 than female in terms of both protein and mRNA. Moreover, in female livers the expression of AQP9 was mostly confined to perivascular hepatocytes, whereas males showed a more homogeneous hepatocyte staining. No differences in AQP9 expression level related to the age or to protein content of the diet were found, indicating that differences in the liver may be gender-dependent. In the brain, AQP9 expression was found in tanycytes mainly localized in the areas lacking a blood-brain barrier (BBB), such as the circumventricular organs (CVOs) of the third ventricles, the subfornical organ, the hypothalamic regions, and the glial processes of the pineal gland. AQP9 expression in the osmosensitive region of the brain suggests a role in the mechanism of central osmoreception. All these findings show a unique tissue distribution of AQP9 compared to the other known aquaporins.

The taste of fat elevates postprandial triacylglycerol

To explore the contributions of taste and smell stimulation by dietary fat on the postprandial rise of serum triacylglycerol (TAG), 19 healthy, overnight-fasted adults received lipid loads (50 g safflower oil in capsules) followed by oral (i.e., taste and smell) or odor-only stimulation with cream cheese on crackers or no load with odor or no stimulation. In eight participants, lipid loading was followed by taste-only stimulation. Stimulation was provided (where applicable) at 3-min intervals for 60 min and 15-min intervals for an additional 60 min. Blood was drawn at stipulated times. Fat loading with oral stimulation led to serum TAG concentrations that were significantly elevated over baseline at 2, 4, and 6 h. Fat loading with odor stimulation led to a significant rise only at 4 h. No significant elevation was observed with either no-load treatment. Taste-only treatment led to a significantly higher TAG response than all other treatments except loading with oral stimulation. These data provide additional evidence supporting a taste component for human fat perception.

Comparative nuclear magnetic resonance studies of water permeability of red blood cells from maternal venous blood and newborn umbilical cord blood

Comparative morphological and nuclear magnetic resonance (NMR) measurements of the diffusional permeability (Pd) were performed on red blood cells (RBCs) from maternal venous blood and fetal RBCs, isolated from cord blood taken at delivery. Fetal RBC had a diameter of 8.79+/-0.03 microm (mean+/-standard deviation, SD), a volume of 103 microm3 and a surface area of 157 microm2. We report here the first comparative measurements of Pd of maternal and fetal RBCs by using a Mn2+-doping NMR technique. The values of Pd were, in the case of maternal RBC, 3.7 x 10(-3) cm/s at 15 degrees C, 4.1 x 10(-3) cm/s at 10 degrees C, 4.9 x 10(-3) cm/s at 25 degrees C, 5.2 x 10(-3) cm/s at 30 degrees C and 7.2 x 10(-3) cm/s at 37 degrees C. For fetal RBC all corresponding Pd values were almost half, namely 2.0 x 10(-3) cm/s at 15 degrees C, 2.3 x 10(-3) cm/s at 20 degrees C, 2.8 x 10(-3) cm/s at 25 degrees C, 3.4 x 10(-3) cm/s at 30 degrees C and 4.4 x 10(-3) cm/s at 37 degrees C. The decreased Pd values of fetal RBCs were probably due to lower channel-mediated water permeability compared with adult RBCs. The values of the activation energy for water permeability (E(a,d)) were significantly higher for fetal RBCs (27.6+/-5.0 kJ/mol) than for adult RBCs (22.8+/-2.7 kJ/mol). A positive correlation between the Pd values of the two kinds of RBCs was found. This points to the genetic basis for the determination of RBC water permeability.

The water channel aquaporin-8 is mainly intracellular in rat hepatocytes, and its plasma membrane insertion is stimulated by cyclic AMP

We previously found that water transport across hepatocyte plasma membranes occurs mainly via a non-channel mediated pathway. Recently, it has been reported that mRNA for the water channel, aquaporin-8 (AQP8), is present in hepatocytes. To further explore this issue, we studied protein expression, subcellular localization, and regulation of AQP8 in rat hepatocytes. By subcellular fractionation and immunoblot analysis, we detected an N-glycosylated band of approximately 34 kDa corresponding to AQP8 in hepatocyte plasma and intracellular microsomal membranes. Confocal immunofluorescence microscopy for AQP8 in cultured hepatocytes showed a predominant intracellular vesicular localization. Dibutyryl cAMP (Bt(2)cAMP) stimulated the redistribution of AQP8 to plasma membranes. Bt(2)cAMP also significantly increased hepatocyte membrane water permeability, an effect that was prevented by the water channel blocker dimethyl sulfoxide. The microtubule blocker colchicine but not its inactive analog lumicolchicine inhibited the Bt(2)cAMP effect on both AQP8 redistribution to cell surface and hepatocyte membrane water permeability. Our data suggest that in rat hepatocytes AQP8 is localized largely in intracellular vesicles and can be redistributed to plasma membranes via a microtubule-depending, cAMP-stimulated mechanism. These studies also suggest that aquaporins contribute to water transport in cAMP-stimulated hepatocytes, a process that could be relevant to regulated hepatocyte bile secretion.

Expression and localization of epithelial aquaporins in the adult human lung

Aquaporins (AQPs) facilitate water transport across epithelia and play an important role in normal physiology and disease in the human airways. We used in situ hybridization and immunofluorescence to determine the expression and cellular localization of AQPs 5, 4, and 3 in human airway sections. In nose and bronchial epithelia, AQP5 is expressed at the apical membrane of columnar cells of the superficial epithelium and submucosal gland acinar cells. AQP4 was detected in basolateral membranes in ciliated ducts and by in situ in gland acinar cells. AQP3 is present on basal cells of both superficial epithelium and gland acinus. In these regions AQPs 5, 4, and 3 are appropriately situated to permit transepithelial water permeability. In the small airways (proximal and terminal bronchioles) AQP3 distribution shifts from basal cell to surface expression (i.e., localized to the apical membrane of proximal and terminal bronchioles) and is the only AQP identified in this region of the human lung. The alveolar epithelium has all three AQPs represented, with AQP5 and AQP4 localized to type I pneumocytes and AQP3 to type II cells. This study describes an intricate network of AQP expression that mediates water transport across the human airway epithelium.

Fibroblast contractility: usual interstitial pneumonia and nonspecific interstitial pneumonia

The aim of this study was to compare the function of lung fibroblasts obtained from surgically biopsied specimens of patients with idiopathic pulmonary fibrosis/usual interstitial pneumonia (UIP; n = 5), nonspecific interstitial pneumonia (NSIP; n = 5), and normal parts of surgically resected lungs (control; n = 5). The results showed that (1) fibroblasts obtained from UIP showed increased contractility compared with those obtained from NSIP or controls (UIP, 72.7 +/- 6.21%; NSIP, 32.8 +/- 5.46; controls, 28.5 +/- 3.51, p < 0.01 in UIP versus NSIP or control); (2) this increase in contractility was consistent with enhanced F-actin content in fibroblasts; (3) conditioned media from UIP fibroblast cultures enhanced control fibroblast contractility, whereas those obtained from NSIP or controls did not; (4) the 180 and 25 kD products representing the contractility in conditioned media were identified as fibronectin (ED-A domain) and TGF-beta1 by immunoblots, respectively; (5) the UIP-conditioned media contained higher amounts of fibronectin or TGF-beta 1 (fibronectin: UIP 289 +/- 47.1 ng/ml, NSIP 121 +/- 23.0, control 118 +/- 16.0; TGF-beta1: UIP 798 +/- 119 pg/ml, NSIP 246 +/- 69.1, control 247 +/- 53.6, p < 0.01 in UIP versus NSIP or control); () the contractility positively correlated with the amount of either fibronectin (r = 0.867, p < 0.001, n = 15) or TGF-beta 1 (r = 0.939, p < 0.001, n = 15), respectively. Thus, UIP fibroblasts showed greater contractility than did NSIP fibroblasts and up-regulated control fibroblasts.

Comparative studies of the protein composition of red blood cell membranes from eight mammalian species

The polypeptide pattern of red blood cell (RBC) membranes from cow, sheep, horse, rabbit, guinea pig, rat, mouse, analyzed by polyacrylamide gel electrophoresis, was compared to human RBC counterpart. Some qualitative and quantitative differences were noted. Among the high molecular weight components the bands 2.1-2.3 appeared slightly decreased in rabbit and rat and increased in sheep RBC membranes. Band 3 appeared to have a higher molecular weight in the cow, guinea pig and mouse RBCs, and a lower molecular weight in the sheep RBCs. Band 4.1 from the RBC membranes of cow, sheep, rabbit and guinea pig was splitted into two sub-bands, while band 4.2 overlapped with band 4.1 in horse and guinea pig RBC membranes. There are marked differences in the number and position of bands in the 4.5 region, while band 4.9 is present in higher amounts in horse, rabbit and guinea pig RBC membranes. Band 6 (glyceraldehyde 3-phosphate dehydrogenase) was undetectable in horse, rat and mouse RBC membranes and was decreased in sheep, rabbit and guinea pig. There are also major differences in the region of band 7 and below ("post-7"). Band 8 was undetectable in horse, cow and guinea pig, and was in higher amounts in rat. A band corresponding to a molecular weight of about 22 kD in the "post-8" region was present only in guinea pig RBC membranes.