Cylindrical Phycobilisomes from a Blue-Green Alga, Anabaena variabilis

Cylindrical 52.5-nm-long phycobilisomes were observed in Anabaenavariabilis, differing from the generally accepted hemidiscoidalmorphology. The central part of such a phycobilisome has a network-likefine structure of slightly greater diameter (16 nm) than theconnected end parts of stacked-disc structure (12 nm in diameter).On the basis of this morphology, the molecular mass of thisphycobilisome was calculated to be 3.27?10⁶, about 60% of whichis accounted for by phycocyanin with the rest being due to allophycocyanin.Separately prepared 23 S allophycocyanin particles with a molecularmass of 1.13?10⁶ have the dimensions (16?23 nm) and network-likefine structure similar to the central part of phycobilisomes,while an aggregate form of phycocyanin (18 S) has a fine structureof stacked discs similar to the connecting end part of phycobilisomes,suggesting that the central part constitutes the core at whichthese phycobilisomes attach to the thylakoid membranes. (Received June 5, 1982; Accepted September 21, 1982)     

Dissociation Kinetics of Anabaena Phycobilisomes

The dissociation kinetics of Anabaena phycobilisomes (PBS) atlow phosphate concentrations was studied with light scatteringand sensitized fluorescence arising from allophycocyanin-I (APC-I).When curve fitting was applied to the decrement time-coursesof these two characters, both fitted the same type of decaykinetics consisting of three sequential phases of first-orderdecay, and the rate constants of these phases were practicallythe same between changes of light scattering and sensitizedfluorescence. As the light scattering reflects the particlesize, the conformity of the two kinetics indicates that theuncoupling of excitation energy transfer originated from thedissociation of PBS. The fluorescence emission spectra of dissociating PBS were resolvableinto three- component spectra, those of phycocyanin (PC) hexamer,APC trimer and APC-I. In the first and second phases of dissociation,the emission from PC increased with concomitant decrease inthe emission from APC and APC-I with the ratio of APC to APC-Iunaltered, while in the third phase the transfer from APC toAPC-I was completely disrupted. These results support the viewthat the whole PBS consists of two moieties of PC subparticleand one moiety of APC-APC-I complex. (Received March 1, 1982; Accepted May 10, 1982)     

Comparison of main emissions at--196?C from phycobilisomes of two blue-green algae Anabaena cylindrica and Anacystis nidulans

Main emissions at—196?C from phycobilisomes of two blue-greenalgae Anabaena cylindrica and Anacystis nidulans were studiedwith special reference to allophycocyanin (APC) B content. Supplementaryexperiments were done with Anabaena variabilis (M-2 and M-3).The main emission from phycobilisome of Anacystis nidulans richin APC B was located at 681 nm. The location was identical tothat of the main emission from APC B but at a shorter wavelengththan that of in vivo emission (685 nm). Results indicate thatAPC B acts as the energy output of phycobilisomes, but thatthe in vivo 685 nm emission is not attributed to APC B. The main emission of the phycobilisome of Anabaena cylindricawas always located at 685 nm irrespective of the preparationmethod; 0.75 M phosphate buffer [Plant Physiol., 63: 615–620(1979)] or 30% polyethylene glycol [Special Issue of Plant &Cell Physiol., No. 3, p. 23–31 (1977)]. This alga alsocontained a special form of APC, but its content was very low.The location of its emission band (681 nm) was identical tothat of APC B, but shorter than that of the main band of phycobilisomes(685 nm). The 685 nm emitter in phycobilisomes showed a charactersimilar to chlorophyll a but not phycobiliproteins in treatmentsfor aqueous extraction or methanol extraction. Results indicatethat the pigment is probably chlorophyll a as we assumed previously.The 685 nm emission from phycobilisomes of Anabaena variabilis(M-2 and M-3) showed the same character. Results were interpreted as indicating that (i) the contentof the special form of APC varies with the species or strainof blue-green algae and (ii) the energy at the phycobilin levelis transferred directly from APC to pigment system II chlorophylla when the amount of the special form of APC is low. (Received October 24, 1979; )     

Characterization and Translation of Poly(A)+RNA from Wounded and Crown Gall Tissues of Potato Tubers

Poly(A)⁺ and poly(A)^–RNA from wounded potato tuber tissuesand crown gall tumors were separated from total RNA by oligodeoxythymidylicacid-cellulose affinity chromatography. The poly(A)⁺RNA wascharacterized by sucrose density gradient centrifugation, hybridizationwith ³(H)polyuridylic acid [Poly(U)] and in vitro translationin a rabbit reticulocyte lysate system. The tumor poly(A)⁺RNAwas a heterodisperse mixture from 3.5S to 35S. Upon poly(U)hybridization of the gradient fractions two major hybridizationpeaks at 7S and 21S and two peaks at 11S and 16S appeared. Inan in vitro translation system the poly(A)⁺RNA programmed thesynthesis of 23 different polypeptides of 9,000 to 79,800 daltonsmolecular weight as determined by SDS-polyacrylamide gel electrophoresis.The 21S poly(A)+RNA was about 5 times more active in in vitroprotein synthesis than the 7S poly(A)⁺RNA. The poly(A)⁺RNA from wounded tissues was also heterodisperse(from 4.5S to 31S) with a modal peak at 18S. This RNA codedfor at least 28 polypeptides, which were different from thoseof crown gall tumor tissues. On a per unit poly(A)⁺RNA basis the tumor RNA was slightly moreactive in translation than that from wounded tissues. The translationof tumor poly(A)⁺RNA was completely blocked by 0.5 mM 7-methylguanosine5'-phosphate, but not by 7-methylguanosine, suggesting the presenceof a 5'-cap structure. (Received May 15, 1982; Accepted June 30, 1982)     

Ontogeny, Phytogeny, and Cellular Cooperation

The capacity of adult newt (Triturus viridescens) spleen cellsto secrete antibody at 4 C allows simultaneous visualizationand quantification of non-secretory (S^–) and secretory(S⁺) rosette forming cells (RFC). Visualization of mammalianS⁺ RFC requires 37 C, a temperature at which S^– RFC appearto be fragile. RFC can be distinguished as S^– or S⁺ dueto whether one or more layers of erythrocytes adhere to thesurface of sensitized spleen cells. Different doses of horseerythrocytes (HRBC) affect newt S^– RFC and S⁺ RFC differentially.By varying the time between injections of different concentrationsof chicken erythrocytes (CRBC, the "carrier") and a constantdosage of CRBC-TNP (trinitrophenyl, the hapten) it is possibleto measure "helper" activity that correlates with the populationof S^– RFC and is both dose and time dependent. By varyingassay time after "helper" activity has been maximized, one candetermine the cytodynamics of anti-TNP antibody producing cell(APC) activity. For the first time these morphologically separableRFC can be related to their suspected physiologic behavior.A shift from S^– RFC to S⁺ RFC takes place during the immuneresponse. That similar dose-dependent response curves can beshown in adultRana pipiens suggests that the newt responsesrepresent a fundamental vertebrate pattern.     

Phycobilisomes of wild type and pigment mutants of the cyanobacterium Synechocystis PCC 6803

Mutants affected in their pigment content and in the structure of their phycobilosomes (PBS) were isolated in the cyanobacterium Synechocystis PCC 6803 by enriching a population with the inhibitor p-hydroxymercuribenzoate. Three of these mutants, PMB 2, PMB 10 and PMB 11, with original phenotypes, are described. Applying several criteria of analysis (77K absorption and fluorescence, protein electrophoretic patterns, electron microscopy), it was possible to assign the component polypeptides to each substructure of the phycobilisome. The model structure obtained fits with those described in other species PMB 10 and PMB 11, completely lacking PC, are the first source of pure PBS cores available, in which no contamination by residual PC can be feared, and are thus particularly interesting for further biochemical studies. The capacity of genetic transformation of Synechocystis PCC 6803 by chromosomal DNA makes this system very convenient for the analysis of the regulation of synthesis of the PBS constituents.Abbreviations PSI, PSII photosystems I, II - PBS phycobilisomes - PC phycocyanin - APC allophycocyanin - APC-B alophycocyanin B - PE phycoerythrin - PEC phycoerythrocyanin - WT wind type - Chl chlorophyll Present address: Service de Physiologie Microbienne Institut Pasteur, 28, rue du Docteur Roux, F-75724 Paris Cedex 15, France     

PHYCOBILIPROTEIN COMPOSITION AND CHLOROPLAST STRUCTURE IN THE FRESHWATER RED ALGA COMPSOPOGON COERULEUS (RHODOPHYTA)1

Serial sections of uncorticated axial cells of Compsopogon coeruleus revealed a single interconnected parietal chloroplast. Phycobilisomes in such chloroplasts were hemidiscoidal in shape with a broad-face diameter of ca. 25–30 nm. The molar ratio of phycobiliproteins in whole cell extracts was IPE:3PC:1APC, similar to isolated phycobilisomes. Two spectrally distinct C-phycocyanin forms (A618 nm, F648 nm and A630 nm, F652 nm) were resolved in dissociated phycobilisomes along with B-phycoerythrin and allophycocyanin.     

An Evidence Indicating That a Weak Orange Light Absorbed by Phycobilisomes Causes Inactivation of PSII in Cells of the Red Alga Porphyridium cruentum Grown under a Weak Red Light Preferentially Exciting Chl a

Changes in the PSII fluorescence upon shift of light qualitywere studied with the red alga Porphyridium cruentum IAM R-1and supplementarily with P. cruentum ATCC 50161, the cyanophytesSynechocystis spp. PCC6714 and PCC6803 and Synechococcus sp.NIBB1071. When Porphyridium cruentum grown under a weak redlight (PSI light) preferentially absorbed by Chl a was illuminatedwith a weak orange light (PSII light) mainly absorbed by phycobilisomes(PBS), a change of PSII fluorescence at room temperature wasinduced. The ratio of Fvm (Fm— Fo) to Fm was reduced rapidlyaccompanying the increase in Fo (T^1/2 ca. 3 min). The effectsof DCMU and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinoneindicated that the fluorescence change is induced when plastoquinonepool is highly reduced. The fluorescence change after a shortPSII light illumination was reversible; it rapidly recoveredin the dark (T ^1/2 ca. 3 min). The reversibility was graduallyreduced and disappeared after 40 h under PSII light accompanyingdecrease in PSII activity per PBS down to almost 50%. Sincethe pattern of the fluorescence change resembles that observablewhen PSII is photoinactivated, PSII light probably induces thephotoinactivation of PSII, possibly reversibly at first andirreversibly after prolonged illumination. Such a rapid fluorescencechange was insignificant in Synechocystis sp. either PCC6714or PCC6803. Only a slow and small decrease in Fvm/Fm level appearedafter prolonged PSII light illumination (the reduction of PSIIactivity per PBS was around 20%). In Porphyridium, shift fromPSII light to PSI light caused a rapid and chloramphenicol-sensitiveFvm/Fm elevation during the first 10 h while the increase inPSH activity per PBS was only 10% of that before the light shift.Then, a gradual elevation followed up to the level at the steadystate under PSI light. A similar rapid increase in Fvm/Fm wasobserved with Synechocystis PCC6714, in which the synthesisof PSII is not regulated, suggesting that a rapid increase inFvm/Fm does not reflect the acceleration of the synthesis ofPSII. Results were interpreted as that (1) PSII light causesphotoinactivation of PSII. Such a photoinactivation is markedin Prophyridium cells grown under PSI light. (2) In Porphyridium,changes in the abundance of PSII upon shift of light qualityare largely attributed to the photoinactivation of this type. (Received February 19, 1999; Accepted June 14, 1999)     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling     

Phycobilisomes of Porphyridium cruentum. I. Isolation

A procedure was developed for the isolation of phycobilisomes from Porphyridium cruentum. The cell homogenate, suspended in phosphate buffer (pH 6.8), was treated with 1% Triton X-100, and its supernatant fraction was centrifuged on a sucrose step gradient. Phycobilisomes were recovered in the 1 M sucrose band. The phycobilisome fraction was identified by the characteristic appearance of the phycobilisomes, and the absorbance of the component pigments: phycoerythrin, R-phycocyanin, and allophycocyanin Isolated phycobilisomes had a prolate shape, with one particle axis longer than the other. Their size varied somewhat with their integrity, but was about 400–500 A (long axis) by 300–320 A (short axis). Phycobilisome recovery was determined at six phosphate buffer concentrations from 0.067 M to 1.0 M. In 0.5 M phosphate, phycobilisome yield (60%) and preservation were optimal. Such a preparation had a phycoerythrin 545 nm/phycocyanin 620 nm ratio of 8.4. Of the detergents tested (Triton X-100, Tween 80, and sodium deoxycholate), Triton X-100 gave the best results Freezing of the cells caused destruction of phycobilisomes.     

Metabolism of S-methylcysteine and pectin esterification in Chinese cabbage, Brassica pekinensis Rupr.

S-Methyl-L-cysteine was actively metabolized in Chinese cabbageand carbon from its methyl group was distributed into both thesoluble and insoluble fractions. The high incorporation of ¹⁴Cfrom the methyl group into the insoluble fraction after administeringof S-methyl-L-cysteine-¹⁴CH₃, and our previous results thatS-methyl-L-cysteine is demethylated to give cysteine, suggestthat S-methyl-L-cysteine might act as a methyl donor in Chinesecabbage. To obtain evidence for this possibility, incorporationof the methyl-¹⁴C of S-methyl-L-cysteine into methyl estersof pectic substances was investigated. Most of the ¹⁴C incorporatedinto pectic substances was liberated by treatment with dilutealkali and pectin esterase. The results show that S-methyl-L-cysteineacts as a methyl donor to form pectin ester. (Received October 12, 1971; )     

Preparation and Characterization of Heat-Stable and Very Active Oxygen-Evolving Photosystem II Particles from the Thermophilic Cyanobacterium, Synechococcus elongatu

Very active and heat-stable oxygen-evolving photosystem II particleswere isolated from the thermophilic cyanobacterium Synechococcuselongatus by treatment of thylakoid membranes with a non-ionicdetergent, sucrose monolaurate (SML). The particles were analyzedin a comparison with photosystem II particles prepared withß-octylglucoside (OG). The two preparations had similarpolypeptide compositions, which were caracterized by high levelsof polypeptides from phycobilisomes. The ratio of chlorophylla to QA was 45 and there were four Mn atoms and one tightlybound Ca²⁺ ion per QA in the particles prepared with SML. Thepreparations were thermophilic, showing substantial rates ofoxygen evolution at temperatures up to 60°C. The maximumrates attained at 45°C were as high as 6.0 mmoles O₂ mg^–1Chl h^–1. PS II particles prepared with OG were similarlythermostable but were less active in oxygen evolution at alltemperatures examined. Kinetic analysis of flash-induced absorptiontransients revealed that about 22% and 28% of photosystem IIreaction centers were not associated with the functional QBsite in the SML- and OG-particles, respectively. When correctedfor the inactive reaction centers, the maximum rates of oxygenevolution by SML- and OG-particles were 7.7 and 7.0 mmoles O₂mg^–1 Chl h^–1, which correspond to half times of1.9 and 2.1 ms for the first-order electron transfer, respectively.Comparison of these half times with those of the S-state transitionand the release of oxygen indicates that the overall photosystemII electron transport is limited by the reduction of added electronacceptors and not by release of oxygen. ³On leave from National Chemical Laboratory for Industry, Higashi1-1, Tsukuba, Ibaraki 305     

Microheterogeneity of N-glycosylation on a stylar self-incompatibility glycoprotein of Nicotiana alata

Gametophytic self-incompatibility, a mechanism that preventsinbreeding in some families of flowering plants, is mediatedby the products of a single genetic locus, the S-locus. Theproducts of the S-gene in the female sexual tissues of Nicotianaalata are an allelic series of glycoproteins with RNase activity.In this study, we report on the microheterogeneity of N-linkedglycosylation at the four potential N-glycosylation sites ofthe S²-glycoprotein. The S-glycoproteins from N.alata containfrom one to five potential N-glycosylation sites based on theconsensus sequence Asn-Xaa-Ser/Thr. The S²-glycoprotein containsfour potential N-glycosylation sites at Asn²⁷, Asn³⁷, Asn¹³⁸and Asn¹⁵⁰, designated sites I, n, IV and V, respectively. SiteIII is absent from the S₂-glycoprotein. Analysis of glycopeptidesgenerated from the S₂-glycoprotein by trypsin and chymotrypsindigestions revealed the types of glycans and the degree of microheterogeneitypresent at each site. Sites I (Asn²⁷) and IV (Asn¹³⁸) displaymicroheterogeneity, site II (Asn³⁷) contains only a single typeof N-glycan, and site V (Asn¹⁵⁰) is not glycosylated. The microheterogeneityobserved at site I on the S₂-glycoprotein is the same as thatobserved at the only site, site I, on the Srglycoprotein (Woodwardet al., Glycobiology, 2, 241-250, 1992). Since the N-glycosylationconsensus sequence at site I is conserved in all S-glycoproteinsfrom other species of self-incompatible solanaceous plants,glycosylation at this site may be important to their function.No other post-translational modifications (e.g. O-glycosylation,phosphorylation) were detected on the S₂-glycoprotein. fertilization microheterogeneity N-glycans plants RNase     

Mercury-Induced Inhibition of Photosystem II Activity and Changes in the Emission of Fluorescence from Phycobilisomes in Intact Cells of the Cyanobacterium, Spirulina platensis

Addition of low concentrations of mercury chloride (HgCl₂ tointact cells of the cyanobacterium, Spirulina platensis causedan enhancement in the intensity of fluorescence emitted fromphycocyanin at room temperature and induced blue shifts in theemission peak suggestive of changes in energy transfer withinthe phycobilisomes. HgCl₂ also suppressed the whole-chain electrontransport activity (H₂O methylviologen) at much lower concentrationsthan that required to inhibit Hill activity supported by para-benzoquinone.The extent of inhibition of Hill activity was much higher underhigh-intensity light than that under low-intensity light. Ourresults indicate that mercury ions at low concentrations affectthe transfer of energy within phycobilisomes and at high concentrationsthey inhibit electron transport in this cyanobacterium. (Received February 21, 1989; Accepted October 2, 1989)     

Ultrastructural Comparison of Cyanidium caldarium Wild Type and III-C Mutant Lacking Phycobilisomes

Cyanidium caldarium wild type and III-C mutant lacking phycobilisomes were compared with respect to the ultrastructural organization of particles on the freeze-fractured thylakoid membrane.     

Phycobilisomes from blue-green and red algae: isolation criteria and dissociation characteristics

A general procedure for the isolation of functionally intact phycobilisomes was devised, based on modifications of previously used procedures. It has been successful with numerous species of red and blue-green algae (Anabaena variabilis, Anacystis nidulans, Agmenellum quadruplicatum, Fremyella diplosiphon, Glaucosphaera vacuolata, Griffithsia pacifica, Nemalion multifidum, Nostoc sp., Phormidium persicinum, Porphyridium cruentum, P. sordidum, P. aerugineum, Rhodosorus marinus). Isolation was carried out in 0.75 molar K-phosphate (pH 6.8 to 7.0) at 20 to 23 C on sucrose step gradients. Lower temperature (4 to 10 C) was usually unfavorable resulting in uncoupling of energy transfer and partial dissociation of the phycobilisomes, sometimes with complete loss of allophycocyanin. Intact phycobilisomes were characterized by fluorescence emission peaks of 670 to 675 nanometers at room temperature, and 678 to 685 nanometers at liquid nitrogen temperature. Uncoupling and subsequent dissociation of phycobilisomes, in lowered ionic conditions, varied with the species and the degree of dissociation but occurred preferentially between phycocyanin and allophycocyanin, or between phycocyanin and phycoerythrin.     

Mercury Induces Alteration of Energy Transfer in Phycobilisome by Selectively Affecting the Pigment Protein, Phycocyanin, in the Cyanobacterium, Spirulina platensis

Mercury, at a low concentration (3 µM) caused an enhancementin the intensity of room temperature fluorescence emitted byphycocyanin and induced a blue shift in the emission peak ofSpirulina cells indicating the alterations in the energy transferwithin the phycobilisomes. In vitro the isolated intact Spirulinaphycobilisomes from control cells exhibited only a reductionin fluorescence yield with low concentration of HgCl₂ withoutbeing accompanied by changes in the emission features, whereasthe isolated phycobilisomes from mercury treated cells exhibitedthe alterations in the spectral characteristics at the levelof phycocyanin. When isolated phycocyanin and allophycocyaninwere exposed to very low concentrations of Hg²* ions, C-phycocyaninexhibited a large decrease in the absorbance in the longer wavelength(615–620 nm) region, but not allophycocyanin. In addition,mercury also caused a monotonous decrease in the C-phycocyaninemission intensity at 646 nm accompanied by a blue shift to642 nm. These results on isolated C-phycocyanin suggest thatselective bleaching of beta-84 chromophore of phycocyanin isinduced by mercury. The differential effect of mercury towardsC-phycocyanin and allophycocyanin could possibly be due to thedifference in the protein conformation of phycocyanin and allophycocyanin. (Received July 11, 1990; Accepted December 17, 1990)     

Heightened epithelial Na+ channel-mediated Na+ absorption in a murine polycystic kidney disease model epithelium lacking apical monocilia

The Tg737°^rpk autosomal recessive polycystic kidney disease (ARPKD) mouse carries a hypomorphic mutation in the Tg737 gene. Because of the absence of its protein product Polaris, the nonmotile primary monocilium central to the luminal membrane of ductal epithelia, such as the cortical collecting duct (CCD) principal cell (PC), is malformed. Although the functions of the renal monocilium remain elusive, primary monocilia or flagella on neurons act as sensory organelles. Thus we hypothesized that the PC monocilium functions as a cellular sensor. To test this hypothesis, we assessed the contribution of Polaris and cilium structure and function to renal epithelial ion transport electrophysiology. Properties of Tg737°^rpk mutant CCD PC clones were compared with clones genetically rescued with wild-type Tg737 cDNA. All cells were grown as polarized cell monolayers with similarly high transepithelial resistance on permeable filter supports. Three- to fourfold elevated transepithelial voltage (V_te) and short-circuit current (I_sc) were measured in mutant orpk monolayers vs. rescued controls. Pharmacological and cell biological examination of this enhanced electrical end point in mutant monolayers revealed that epithelial Na⁺ channels (ENaCs) were upregulated. Amiloride, ENaC-selective amiloride analogs (benzamil and phenamil), and protease inhibitors (aprotinin and leupeptin) attenuated heightened V_te and I_sc. Higher concentrations of additional amiloride analogs (ethylisopropylamiloride and dimethylamiloride) also revealed inhibition of V_te. Cell culture requirements and manipulations were also consistent with heightened ENaC expression and function. Together, these data suggest that ENaC expression and/or function are upregulated in the luminal membrane of mutant, cilium-deficient orpk CCD PC monolayers vs. cilium-competent controls. When the genetic lesion causes loss or malformation of the monocilium, ENaC-driven Na⁺ hyperabsorption may explain the rapid emergence of severe hypertension in a majority of patients with ARPKD. cilia; hypertension; ion transport; epithelial cells