Use of a Modified Matrix Band Technique to Restore Subgingival Root Caries

Given the increasing incidence of root caries in the elderly population, clinicians frequently must isolate and restore subgingival preparations. This article demonstrates a technique utilizing a modified Tofflemire matrix band that creates a preparation free of crevicular fluid and blood for restoration with resin-modified glass ionomer cement.

Effect of Sonic Resin Composite Delivery on Void Formation Assessed by Micro-computed Tomography

OBJECTIVES

The aim of this study was to quantify the internal void volume formation in commercially available, resin composites inserted using conventional or sonic insertion methods, and analyzed using three-dimensional (3D) micro-computed tomography (μCT).

METHODS AND MATERIALS

Four resin composites were evaluated: one conventional (Herculite, Ultra, Kerr Corporation, Orange, CA, USA), one flowable bulk fill (SureFil SDR Flow, Dentsply International, York, PA, USA), and two packable bulk fill (SonicFill, Kerr Corporation, and Tetric EvoCeram Bulk Fill, Ivoclar Vivadent Inc, Schaan, Liechtenstein). Eight groups were evaluated according to each resin composite type and insertion method (conventional or sonic; n=5). Forty ABS 3D-printed cylindrical molds, 5.0 mm in diameter and 4.0 mm in depth, were fabricated. For the conventional resin composite, the mold was filled incrementally (two layers), while for bulk-fill resin composites, insertion was performed in a single increment. The sonic insertion method was performed using a specific handpiece (SonicFill Handpiece, Kerr Corporation). Resin composites were light cured using a multipeak light-emitting diode light-curing unit (VALO, Ultradent Products Inc, South Jordan, UT, USA) in its regular mode. Samples were evaluated by μCT, and data were imported into software (Amira, version 5.5.2, VSG, Burlington, MA, USA) for 3D reconstruction, from which the percentage of void volume was calculated. Data were analyzed using two-way analysis of variance and Tukey post hoc test at a preset alpha of 0.05.

RESULTS

The conventional insertion method resulted in reduced porosity, compared with sonic insertion, for SureFil SDR Flow and Tetric EvoCeram bulk fill. The sonic insertion method did not demonstrate any influence on void formation for Herculite Ultra or SonicFill.

CONCLUSION

Results suggest that the sonic insertion method might increase void formation during resin composite delivery, depending on restorative material brand.

Replacement of a Missing Maxillary Central Incisor Using a Direct Fiber-Reinforced Fixed Dental Prosthesis: A Case Report

The use of the direct fiber-reinforced fixed dental prosthesis (FDP) restorative technique presented in this article will result in an ideal restoration considering both esthetics and function in a single appointment. Although indirect techniques are available and may be used, they are time-consuming, resulting in higher cost; therefore, a simplified approach combining a prebonded fiber-reinforced mesh with a sculptable micro-hybrid composite will deliver an acceptable esthetic result with proper function.

Restorative Technique Selection in Class IV Direct Composite Restorations: A Simplified Method

Use of the techniques presented here will yield highly esthetic resin composite restorations in minimal time. Although more elaborate composite layering techniques exist and may be used in complex esthetic scenarios, a simplified approach combining two body shades and implementing basic dental anatomy concepts often will deliver highly acceptable esthetic results.

A mutation in mitochondrial 12S rRNA, A827G, in Argentinean family with hearing loss after aminoglycoside treatment

Mutations in mitochondrial DNA (mtDNA) have been found to be associated with sensorineural hearing loss. We report the clinical, genetic, and molecular characterization of one Argentinean family with aminoglycoside-induced impairment in two of their members. Clinical evaluation revealed the variable phenotype of hearing impairment including audiometric configuration in these subjects. Mutational analysis of the mtDNA in these pedigrees showed the presence of homoplasmic 12S rRNA A827G mutation, which has been associated with hearing impairment. The A827G mutation is located at the A-site of the mitochondrial 12S rRNA gene which is highly conserved in mammals. It is possible that the alteration of the tertiary or quaternary structure of this rRNA by the A827G mutation may lead to mitochondrial dysfunction, thereby playing a role in the pathogenesis of hearing loss and aminoglycoside hypersensitivity. However, incomplete penetrance of hearing impairment indicates that the A827G mutation itself is not sufficient to produce clinical phenotype.

Human disease-causing NOG missense mutations: effects on noggin secretion, dimer formation, and bone morphogenetic protein binding

Secreted noggin protein regulates bone morphogenetic protein activity during development. In mice, a complete loss of noggin protein leads to multiple malformations including joint fusion, whereas mice heterozygous for Nog loss-of-function mutations are normal. In humans, heterozygous NOG missense mutations have been found in patients with two autosomal dominant disorders of joint development, multiple synostosis syndrome (SYNS1) and a milder disorder proximal symphalangism (SYM1). This study investigated the effect of one SYNS1 and two SYM1 disease-causing missense mutations on the structure and function of noggin. The SYNS1 mutation abolished, and the SYM1 mutations reduced, the secretion of functional noggin dimers in transiently transfected COS-7 cells. Coexpression of mutant noggin with wild-type noggin, to resemble the heterozygous state, did not interfere with wild-type noggin secretion. These data indicate that the human disease-causing mutations are hypomorphic alleles that reduce secretion of functional dimeric noggin. Therefore, we conclude that noggin has both species-specific and joint-specific dosage-dependent roles during joint formation. Surprisingly, in contrast to the COS-7 cell studies, the SYNS1 mutant was able to form dimers in Xenopus laevis oocytes. This finding indicates that there also exist species-specific differences in the ability to process mutant noggin polypeptides.

Localization of endogenous and recombinant Na(+)-driven anion exchanger protein NDAE1 from Drosophila melanogaster

Na(+)-dependent Cl(-)/HCO exchange activity helps maintain intracellular pH (pH(i)) homeostasis in many invertebrate and vertebrate cell types. Our laboratory cloned and characterized a Na(+)-dependent Cl(-)/HCO exchanger (NDAE1) from Drosophila melanogaster (Romero MF, Henry D, Nelson S, Harte PJ, and Sciortino CM. J Biol Chem 275: 24552--24559, 2000). In the present study we used immunohistochemical and Western blot techniques to characterize the developmental expression, subcellular localization, and tissue distribution of NDAE1 protein in D. melanogaster. We have shown that a polyclonal antibody raised against the NH(2) terminus of NDAE1 (alpha CWR57) recognizes NDAE1 electrophysiologically characterized in Xenopus oocytes. Moreover, our results begin to delineate the NDAE1 topology, i.e., both the NH(2) and COOH termini are intracellular. NDAE1 is expressed throughout Drosophila development in the central and peripheral nervous systems, sensilla, and the alimentary tract (Malpighian tubules, gut, and salivary glands). Coimmunolabeling of larval tissues with NDAE1 antibody and a monoclonal antibody to the Na(+)-K(+)-ATPase alpha-subunit revealed that the majority of NDAE1 is located at the basolateral membranes of Malpighian tubule cells. These results suggest that NDAE1 may be a key pH(i) regulatory protein and may contribute to basolateral ion transport in epithelia and nervous system of Drosophila.

The renal Na-HCO3-cotransporter expressed in Xenopus laevis oocytes: inhibition by tenidap and benzamil and effect of temperature on transport rate and stoichiometry

In the present experiments we expressed the rat kidney Na+-HCO3- cotransporter (rkNBC) in Xenopus laevis oocytes to reinvestigate the flux coupling ratio under improved measuring conditions. Essentially the current/voltage (I/V) relationship of isolated inside-out giant membrane patches was measured and the stoichiometric ratio was calculated from the reversal potential (VI=0) of the cotransport current (INBC). INBC was defined as that part of the total current that was suppressed when rkNBC was inhibited. Previously we have used the disulfonic stilbene DIDS to inhibit rkNBC, but we now found that tenidap or benzamil are better suited as inhibitors. Tenidap blocked rkNBC rapidly and reversibly both from the intra- and extracellular surface with half maximal inhibition at 13 micromol/l and it did not cause the same potentially disturbing side effects as DIDS. In addition, we found that the endogenous depolarization-induced Na+ conductance of the oocyte, which may compromise the I/V analysis, can be suppressed by applying 1 mmol/l amiloride to the cytosolic surface of the patch. The new measuring conditions greatly increased the yield of successful experiments. The distribution of 27 measurements of VI=0 obtained at near physiological Na+ and HCO3- concentrations and in absence of Cl-, K+ and cytosolic Ca2+ showed that the calculated stoichiometric ratios closely approached the value of 2 HCO3-:1 Na+ if the expression density of rkNBC was high. This result fully confirms our previous observations. Further experiments showed that the difference between the stoichiometric ratio of 3:1 observed in rat proximal tubule in vivo and the present value is not due to the temperature difference. We conclude that, depending on local modulatory influences, rkNBC can operate with different stoichiometric ratios and the present data and those reported in an accompanying publication [Müller-Berger et al., Pflügers Arch (2001) DOI 10.1007/s004240100592] show that these ratios are integer numbers i.e. either 2:1 or 3:1.

The electrogenic Na+/HCO3- cotransporter, NBC

Electrogenic Na(+)/HCO(3)(-) (NBC) function has been characterized in many mammalian tissues including, kidney, pancreas, and brain. Cloning efforts identified a single cDNA, NBC/NBC1, that possesses all the functional attributes of the electrogenic Na(+)/HCO(3)(-) cotransporter. This NBC clone is related to the anion exchangers and thus forms a bicarbonate transporter superfamily. Presently two N-terminal and one C-terminal isoforms are known. All three isoforms appear to arise from the same gene and seem to have identical function. NBC antibodies have localized NBC isoforms in kidney, pancreas, brain, small intestine, colon, epididymis, eye, heart, liver, salivary glands, stomach, and testis. Functionally, NBC appears HCO(3)(-) and Na(+) selective. NBC stoichiometry in Xenopus oocytes is 1 Na(+) : 2 HCO(3)(-), implicating a possible accessory protein interaction.

Cloning and characterization of a Na+-driven anion exchanger (NDAE1). A new bicarbonate transporter

Regulation of intra- and extracellular ion activities (e.g. H(+), Cl(-), Na(+)) is key to normal function of the central nervous system, digestive tract, respiratory tract, and urinary system. With our cloning of an electrogenic Na(+)/HCO(3)(-) cotransporter (NBC), we found that NBC and the anion exchangers form a bicarbonate transporter superfamily. Functionally three other HCO(3)(-) transporters are known: a neutral Na(+)/ HCO(3)(-) cotransporter, a K(+)/ HCO(3)(-) cotransporter, and a Na(+)-dependent Cl(-)-HCO(3)(-) exchanger. We report the cloning and characterization of a Na(+)-coupled Cl(-)-HCO(3)(-) exchanger and a physiologically unique bicarbonate transporter superfamily member. This Drosophila cDNA encodes a 1030-amino acid membrane protein with both sequence homology and predicted topology similar to the anion exchangers and NBCs. The mRNA is expressed throughout Drosophila development and is prominent in the central nervous system. When expressed in Xenopus oocytes, this membrane protein mediates the transport of Cl(-), Na(+), H(+), and HCO(3)(-) but does not require HCO(3)(-). Transport is blocked by the stilbene 4,4'-diisothiocyanodihydrostilbene- 2, 2'-disulfonates and may not be strictly electroneutral. Our functional data suggest this Na(+) driven anion exchanger (NDAE1) is responsible for the Na(+)-dependent Cl(-)-HCO(3)(-) exchange activity characterized in neurons, kidney, and fibroblasts. NDAE1 may be generally important for fly development, because disruption of this gene is apparently lethal to the Drosophila larva.

An electrogenic Na(+)-HCO(-)(3) cotransporter (NBC) with a novel COOH-terminus, cloned from rat brain

We screened rat brain cDNA libraries and used 5' rapid amplification of cDNA ends to clone two electrogenic Na(+)-HCO(-)(3) cotransporter (NBC) isoforms from rat brain (rb1NBC and rb2NBC). At the amino acid level, one clone (rb1NBC) is 96% identical to human pancreas NBC. The other clone (rb2NBC) is identical to rb1NBC except for 61 unique COOH-terminal amino acids, the result of a 97-bp deletion near the 3' end of the open-reading frame. Using RT-PCR, we confirmed that mRNA from rat brain contains this 97-bp deletion. Furthermore, we generated rabbit polyclonal antibodies that distinguish between the unique COOH-termini of rb1NBC (alpharb1NBC) and rb2NBC (alpharb2NBC). alpharb1NBC labels an approximately 130-kDa protein predominantly from kidney, and alpharb2NBC labels an approximately 130-kDa protein predominantly from brain. alpharb2NBC labels a protein that is more highly expressed in cortical neurons than astrocytes cultured from rat brain; alpharb1NBC exhibits the opposite pattern. In expression studies, applying 1.5% CO(2)/10 mM HCO(-)(3) to Xenopus oocytes injected with rb2NBC cRNA causes 1) pH(i) to recover from the initial CO(2)-induced acidification and 2) the cell to hyperpolarize. Subsequently, removing external Na(+) reverses the pH(i) increase and elicits a rapid depolarization. In the presence of 450 microM DIDS, removing external Na(+) has no effect on pH(i) and elicits a small hyperpolarization. The rate of the pH(i) decrease elicited by removing Na(+) is insensitive to removing external Cl(-). Thus rb2NBC is a DIDS-sensitive, electrogenic NBC that is predominantly expressed in brain of at least rat.

A novel H(+)-coupled oligopeptide transporter (OPT3) from Caenorhabditis elegans with a predominant function as a H(+) channel and an exclusive expression in neurons

We have cloned and functionally characterized a novel, neuron-specific, H(+)-coupled oligopeptide transporter (OPT3) from Caenorhabditis elegans that functions predominantly as a H(+) channel. The opt3 gene is approximately 4.4 kilobases long and consists of 13 exons. The cDNA codes for a protein of 701 amino acids with 11 putative transmembrane domains. When expressed in mammalian cells and in Xenopus laevis oocytes, OPT3 cDNA induces H(+)-coupled transport of the dipeptide glycylsarcosine. Electrophysiological studies of the transport function of OPT3 in Xenopus oocytes show that this transporter, although capable of mediating H(+)-coupled peptide transport, functions predominantly as a H(+) channel. The H(+) channel activity of OPT3 is approximately 3-4-fold greater than the H(+)/peptide cotransport activity as determined by measurements of H(+) gradient-induced inward currents in the absence and presence of the dipeptide using the two-microelectrode voltage clamp technique. A downhill influx of H(+) was accompanied by a large intracellular acidification as evidenced from the changes in intracellular pH using an ion-selective microelectrode. The H(+) channel activity exhibits a K(0.5)(H) of 1.0 microM at a membrane potential of -50 mV. At the level of primary structure, OPT3 has moderate homology with OPT1 and OPT2, two other H(+)-coupled oligopeptide transporters previously cloned from C. elegans. Expression studies using the opt3::gfp fusion constructs in transgenic C. elegans demonstrate that opt3 gene is exclusively expressed in neurons. OPT3 may play an important physiological role as a pH balancer in the maintenance of H(+) homeostasis in C. elegans.

Immunolocalization of anion exchanger AE2 and Na(+)-HCO(-)(3) cotransporter in rat parotid and submandibular glands

Salivary glands secrete K(+) and HCO(-)(3) and reabsorb Na(+) and Cl(-), but the identity of transporters involved in HCO(-)(3) transport remains unclear. We investigated localization of Cl(-)/HCO(-)(3) exchanger isoform AE2 and of Na(+)-HCO(-)(3) cotransporter (NBC) in rat parotid gland (PAR) and submandibular gland (SMG) by immunoblot and immunocytochemical techniques. Immunoblotting of PAR and SMG plasma membranes with specific antibodies against mouse kidney AE2 and rat kidney NBC revealed protein bands at approximately 160 and 180 kDa for AE2 and approximately 130 kDa for NBC, as expected for the AE2 full-length protein and consistent with the apparent molecular mass of NBC in several tissues other than kidney. Immunostaining of fixed PAR and SMG tissue sections revealed specific basolateral staining of PAR acinar cells for AE2 and NBC, but in SMG acinar cells only basolateral AE2 labeling was observed. No AE2 expression was detected in any ducts. Striated, intralobular, and main duct cells of both glands showed NBC expression predominantly at basolateral membranes, with some cells being apically stained. In SMG duct cells, NBC staining exhibited a gradient of distribution from basolateral localization in more proximal parts of the ductal tree to apical localization toward distal parts of the ductal tree. Both immunoblotting signals and immunostaining were abolished in preabsorption experiments with the respective antigens. Thus the mechanisms of fluid and anion secretion in salivary acinar cells may be different between PAR and SMG, and, because NBC was detected in acinar and duct cells, it may play a more important role in transport of HCO(-)(3) by rat salivary duct cells than previously believed.

Cloning and immunolocalization of a rat pancreatic Na(+) bicarbonate cotransporter

In the rat, pancreatic HCO(-)(3) secretion is believed to be mediated by duct cells with an apical Cl(-)/HCO(-)(3) exchanger acting in parallel with a cAMP-activated Cl(-) channel and protons being extruded through a basolateral Na(+)/H(+) exchanger. However, this may not be the only mechanism for HCO(-)(3) secretion by the rat pancreas. Recently, several members of electrogenic Na(+)/HCO(-)(3) cotransporters (NBC) have been cloned. Here we report the cloning of a NBC from rat pancreas (rpNBC). This rpNBC is 99% identical to the longer, more common form of NBC [pNBC; 1079 amino acids (aa); 122 kDa in human heart, pancreas, prostate, and a minor clone in kidney]. The longer NBC isoforms are identical to the rat and human kidney-specific forms (kNBC; 1035 aa; 116 kDa) at the approximately 980 C-terminal aa's and are unique (with different lengths) at the initial N-terminus. Using polyclonal antibodies to the common N- and C-termini of rat kidney NBC, a approximately 130-kDa protein band was labeled by immunoblotting of rat pancreas homogenate and was enriched in the plasma membrane fraction. Immunofluorescence and immunoperoxidase light microscopy of rat pancreatic tissue with both antibodies revealed basolateral labeling of acinar cells. Labeling of both apical and basolateral membranes was found in centroacinar cells, intra- and extralobular duct, and main duct cells. The specificity of the antibody labeling was confirmed by antibody preabsorption experiments with the fusion protein used for immunization. The data suggest that rpNBC likely plays a more important role in the transport of HCO(-)(3) by rat pancreatic acinar and duct cells than previously believed.

Cation and voltage dependence of rat kidney electrogenic Na(+)-HCO(-)(3) cotransporter, rkNBC, expressed in oocytes

Recently, we reported the cloning and expression of the rat renal electrogenic Na(+)-HCO(-)(3) cotransporter (rkNBC) in Xenopus oocytes [M. F. Romero, P. Fong, U. V. Berger, M. A. Hediger, and W. F. Boron. Am. J. Physiol. 274 (Renal Physiol. 43): F425-F432, 1998]. Thus far, all NBC cDNAs are at least 95% homologous. Additionally, when expressed in oocytes the NBCs are 1) electrogenic, 2) Na(+) dependent, 3) HCO(-)(3) dependent, and 4) inhibited by stilbenes such as DIDS. The apparent HCO(-)(3):Na(+) coupling ratio ranges from 3:1 in kidney to 2:1 in pancreas and brain to 1:1 in the heart. This study investigates the cation and voltage dependence of rkNBC expressed in Xenopus oocytes to better understand NBC's apparent tissue-specific physiology. Using two-electrode voltage clamp, we studied the cation specificity, Na(+) dependence, and the current-voltage (I-V) profile of rkNBC. These experiments indicate that K(+) and choline do not stimulate HCO(-)(3)-sensitive currents via rkNBC, and Li(+) elicits only 3 +/- 2% of the total Na(+) current. The Na(+) dose response studies show that the apparent affinity of rkNBC for extracellular Na(+) ( approximately 30 mM [Na(+)](o)) is voltage and HCO(-)(3) independent, whereas the rkNBC I-V relationship is Na(+) dependent. At [Na(+)](o) v(max) (96 mM), the I-V response is approximately linear; both inward and outward Na(+)-HCO(-)(3) cotransport are observed. In contrast, only outward cotransport occurs at low [Na(+)](o) (<1 mM [Na(+)](o)). All rkNBC currents are inhibited by extracellular application of DIDS, independent of voltage and [Na(+)](o). Using ion-selective microelectrodes, we monitored intracellular pH and Na(+) activity. We then calculated intracellular [HCO(-)(3)] and, with the observed reversal potentials, calculated the stoichiometry of rkNBC over a range of [Na(+)](o) values from 10 to 96 mM at 10 and 33 mM [HCO(-)(3)](o). rkNBC stoichiometry is 2 HCO(-)(3):1 Na(+) over this entire Na(+) range at both HCO(-)(3) concentrations. Our results indicate that rkNBC is highly selective for Na(+), with transport direction and magnitude sensitive to [Na(+)](o) as well as membrane potential. Since the rkNBC protein alone in oocytes exhibits a stoichiometry of less than the 3 HCO(-)(3):1 Na(+) thought necessary for HCO(-)(3) reabsorption by the renal proximal tubule, a control mechanism or signal that alters its in vivo function is hypothesized.

[P300 and auditory information processing during natural sleep]

INTRODUCTION

The P300 is elicited, in the waking state and during an 'attention condition', in response to deviant stimuli of an oddball paradigm. This component of event related potentials (ERP) may be a useful research tool in the assessing of cortical sensory processing during normal sleep since a subject does not need to be awake or totally conscious in order to generate a measurable response.

OBJECTIVE

This study used an classical oddball paradigm as a means to assess the auditory information processing during sleep.

PATIENTS AND METHODS

The auditory ERP were registered in twelve healthy volunteers during the waking state and sleep stages II, III-IV and REM. The amplitude, latency and scalp distribution parameters of the positivity observed were contrasted with the results obtained in the waking state.

RESULTS

A 'P300-like' with a significantly smaller peak amplitude and an increment of latency was elicited during stage II and the REM stage of sleep. As in the waking state, the positivity during this sleep stages was maximal at central-parietal regions.

CONCLUSIONS

The response obtained seems to correspond both for the morphology of the potential as for the centro-parietal predominance with a waking P3b component. These results suggest that certain processes of attention and memory-related operations involved in the auditory processing of simple signals remain operative during these sleep stages.

Stoichiometry of the rat kidney Na+-HCO3- cotransporter expressed in Xenopus laevis oocytes

The rat kidney Na+-HCO3- cotransporter (rkNBC) was expressed in Xenopus laevis oocytes and transport via rkNBC was studied with the patch-clamp technique in giant inside/out (i/o) or outside/out (o/o) membrane patches. The current/voltage (I/V) relation(s) of individual patches was(were) determined in solutions containing only Na+ and HCO3- as permeable ions. The current carried by rkNBC (INBC) was identified by its response to changing bath Na+ concentration(s) and quantified as the current blocked by 4, 4'-diisothiocyanatostilbene disulfonate (DIDS). The stoichiometric ratio (q) of HCO3- to Na+ transport was determined from zero-current (reversal) potentials. The results and conclusions are as follows. First, DIDS (250 micromol/l) blocks INBC irreversibly from both the extracellular and the intracellular surface. Second, in the presence of Na+ and HCO3- concentration gradients similar to those which rkNBC usually encounters in tubular cells, q was close to 2. The same value was also observed when the HCO3- concentration was 25 mmol/l throughout, but the Na+ concentration was either high (100 mmol/l) or low (10 mmol/l) on the extracellular or intracellular surface of the patch. These data demonstrate that in the oocyte cell membrane rkNBC works with q=2 as previously observed in a study of isolated microperfused tubules (Seki et al., Pflügers Arch 425:409, 1993), however, they do not exclude the possibility that in a different membrane and cytoplasmic environment rkNBC may operate with a different stoichiometry. Third, in most experiments bath application of up to 2 mmol/l ATP increased the DIDS-inhibitable conductance of i/o patches by up to twofold with a half saturation constant near 0.5 mmol/l. This increase was not associated with a change in q, nor with a shift in the I/V relationship which would suggest induction of active transport (pump current). Since the effect persisted after ATP removal and was not observed with the non-hydrolysable ATP analogue AMP-PNP, it is possible that rkNBC is activated by phosphorylation via protein kinases that might adhere to the cytoplasmic surface of the membrane patch.

Electrogenic Na+/HCO3- cotransporters: cloning and physiology

Bicarbonate and CO2 comprise the major pH buffer of biological fluids. In the renal proximal tubule most of the filtered HCO3- is reabsorbed by an electrogenic Na/HCO3 cotransporter located at the basolateral membrane. This Na+ bicarbonate cotransporter (NBC) was recently cloned. This review highlights the recent developments leading to and since the cloning of NBC: NBC expression cloning, protein features, clone physiology, isoforms and genes, mRNA distribution, and protein distribution. With the NBC amino acid sequence 30-35% identical to the anion exchangers (AE1-3), a superfamily of HCO3- transporters is emerging. Physiologically, NBC is electrogenic, Na+ dependent, HCO3- dependent, Cl- independent, and inhibited by stilbenes (DIDS and SITS). NBC clones and proteins have been isolated from several tissues (other than kidney) thought to have physiologically distinct HCO3- transporters. For example, NBC occurs in pancreas, prostate, brain, heart, small and large intestine, stomach, and epididymis. Finally, there are at least two genes that encode NBC proteins. Possible future directions of research are discussed.

Cloning and characterization of a human electrogenic Na+-HCO-3 cotransporter isoform (hhNBC)

Our group recently cloned the electrogenic Na+-HCO-3 cotransporter (NBC) from salamander kidney and later from mammalian kidney. Here we report cloning an NBC isoform (hhNBC) from a human heart cDNA library. hhNBC is identical to human renal NBC (hkNBC), except for the amino terminus, where the first 85 amino acids in hhNBC replace the first 41 amino acids of hkNBC. About 50% of the amino acid residues in this unique amino terminus are charged, compared with approximately 22% for the corresponding 41 residues in hkNBC. Northern blot analysis, with the use of the unique 5' fragment of hhNBC as a probe, shows strong expression in pancreas and expression in heart and brain, although at much lower levels. In Xenopus oocytes expressing hhNBC, adding 1.5% CO2/10 mM HCO-3 hyperpolarizes the membrane and causes a rapid fall in intracellular pH (pHi), followed by a pHi recovery. Subsequent removal of Na+ causes a depolarization and a reduced rate of pHi recovery. Removal of Cl- from the bath does not affect the pHi recovery. The stilbene derivative DIDS (200 microM) greatly reduces the hyperpolarization caused by adding CO2/HCO-3. In oocytes expressing hkNBC, the effects of adding CO2/HCO-3 and then removing Na+ were similar to those observed in oocytes expressing hhNBC. We conclude that hhNBC is an electrogenic Na+-HCO-3 cotransporter and that hkNBC is also electrogenic.

Immunolocalization of the electrogenic Na+-HCO-3 cotransporter in mammalian and amphibian kidney

Electrogenic cotransport of Na+ and HCO-3 is a crucial element of HCO-3 reabsorption in the renal proximal tubule (PT). An electrogenic Na+-HCO-3 cotransporter (NBC) has recently been cloned from salamander and rat kidney. In the present study, we generated polyclonal antibodies (pAbs) to NBC and used them to characterize NBC on the protein level by immunochemical methods. We generated pAbs in guinea pigs and rabbits by immunizing with a fusion protein containing the carboxy-terminal 108 amino acids (amino acids 928-1035) of rat kidney NBC (rkNBC). By indirect immunofluorescence microscopy, the pAbs strongly labeled HEK-293 cells transiently expressing NBC, but not in untransfected cells. By immunoblotting, the pAbs recognized a approximately 130-kDa band in Xenopus laevis oocytes expressing rkNBC, but not in control oocytes injected with water or cRNA for the Cl-/HCO-3 exchanger AE2. In immunoblotting experiments on renal microsomes, the pAbs specifically labeled a major band at approximately 130 kDa in both rat and rabbit, as well as a single approximately 160-kDa band in salamander kidney. By indirect immunofluorescence microscopy on 0.5-micrometer cryosections of rat and rabbit kidneys fixed in paraformaldehyde-lysine-periodate (PLP), the pAbs produced a strong and exclusively basolateral staining of the PT. In the salamander kidney, the pAbs labeled only weakly the basolateral membrane of the PT. In contrast, we observed strong basolateral labeling in the late distal tubule, but not in the early distal tubule. The specificity of the pAbs for both immunoblotting and immunohistochemistry was confirmed in antibody preabsorption experiments using either the fusion protein used for immunization or similarly prepared control fusion proteins. In summary, we have developed antibodies specific for NBC, determined the apparent molecular weights of rat, rabbit, and salamander kidney NBC proteins, and described the localization of NBC within the kidney of these mammalian and amphibian species.

Auditory event-related potentials to semantic priming during sleep

The present study uses the N400 component of event-related potentials (ERPs) as a processing marker of single spoken words presented during sleep. Thirteen healthy volunteers participated in the study. The auditory ERPs were registered in response to a semantic priming paradigm made up of pairs of words (50% related, 50% unrelated) presented in the waking state and during sleep stages II, III-IV and REM. The amplitude, latency and scalp distribution parameters of the negativity observed during stage II and the REM stage were contrasted with the results obtained in the waking state. The 'N400-like' effect elicited in these stages of sleep showed a mean amplitude for pairs of unrelated words significantly greater than for related pairs and an increment of latency. These results suggest that during these sleep stages a semantic priming effect is maintained actively although the lexical processing time increases.

Effect of expressing the water channel aquaporin-1 on the CO2 permeability of Xenopus oocytes

It is generally accepted that gases such as CO2 cross cell membranes by dissolving in the membrane lipid. No role for channels or pores in gas transport has ever been demonstrated. Here we ask whether expression of the water channel aquaporin-1 (AQP1) enhances the CO2 permeability of Xenopus oocytes. We expressed AQP1 in Xenopus oocytes by injecting AQP1 cRNA, and we assessed CO2 permeability by using microelectrodes to monitor the changes in intracellular pH (pHi) produced by adding 1.5% CO2/10 mM HCO3- to (or removing it from) the extracellular solution. Oocytes normally have an undetectably low level of carbonic anhydrase (CA), which eliminates the CO2 hydration reaction as a rate-limiting step. We found that expressing AQP1 (vs. injecting water) had no measurable effect on the rate of CO2-induced pHi changes in such low-CA oocytes: adding CO2 caused pHi to fall at a mean initial rate of 11.3 x 10(-4) pH units/s in control oocytes and 13.3 x 10(-4) pH units/s in oocytes expressing AQP1. When we injected oocytes with water, and a few days later with CA, the CO2-induced pHi changes in these water/CA oocytes were more than fourfold faster than in water-injected oocytes (acidification rate, 53 x 10(-4) pH units/s). Ethoxzolamide (ETX; 10 microM), a membrane-permeant CA inhibitor, greatly slowed the pHi changes (16.5 x 10(-4) pH units/s). When we injected oocytes with AQP1 cRNA and then CA, the CO2-induced pHi changes in these AQP1/CA oocytes were approximately 40% faster than in the water/CA oocytes (75 x 10(-4) pH units/s), and ETX reduced the rates substantially (14.7 x 10(-4) pH units/s). Thus, in the presence of CA, AQP1 expression significantly increases the CO2 permeability of oocyte membranes. Possible explanations include 1) AQP1 expression alters the lipid composition of the cell membrane, 2) AQP1 expression causes overexpression of a native gas channel, and/or 3) AQP1 acts as a channel through which CO2 can permeate. Even if AQP1 should mediate a CO2 flux, it would remain to be determined whether this CO2 movement is quantitatively important.

Cloning and functional expression of rNBC, an electrogenic Na(+)-HCO3- cotransporter from rat kidney

We have recently cloned the renal electrogenic Na(+)-bicarbonate contransporter of the salamander Ambystoma tigrinum (aNBC) (M. F. Romero, M. A. Hediger, E. L. Boulpaep, and W. F. Boron. FASEB J. 10: 89, 1996; and Nature 387: 409-413, 1997). Here we report the cloning of a mammalian homolog of aNBC, named rNBC for rat Na(+)-bicarbonate cotransporter. NBC constitutes the major route for HCO3- reabsorption and assists in Na+ reabsorption across the basolateral membrane of the renal proximal tubule (PT). We used aNBC as a probe to screen a rat kidney cortex cDNA library in lambda gt10 and identified several clones. Each has an initiator Met and a large open-reading frame followed by a 3'-untranslated region of approximately 500 bp. The 7.5-kb mRNA for rNBC is present in kidney, liver, lung, brain, and heart. In situ hybridization with the rNBC probe in the rat kidney revealed staining in the S2 segment of PT. rNBC encodes a protein of 1,035 amino acids, with a predicted molecular mass of 116 kDa. Its deduced amino acid sequence is 86% identical to that of aNBC. Comparison of both the aNBC and rNBC sequences to the GenBank database reveals a low level of amino acid identity (approximately 30%) to the AE family of Cl-/HCO3- exchangers. Injection of rNBC cRNA into Xenopus oocytes leads to expression of an electrogenic Na(+)-HCO3- contransporter that is qualitatively similar to that of aNBC but at a much lower level. Placement of the rNBC cDNA into the context of a Xenopus expression vector produces a substantial increase in rNBC expression. Addition of 1.5% CO2/10 mM HCO3- elicits a hyperpolarization of > 50 mV and a rapid decrease of intracellular pH (pHi), followed by an increase in pHi. Subsequent removal of Na+ in the presence of CO2/HCO3- causes a depolarization of > 50 mV and a concomitant decrease of pHi. Thus rNBC is in the same newly identified family of Na(+)-linked HCO3- transporters as is aNBC.

Cloning and characterization of a mammalian proton-coupled metal-ion transporter

Metal ions are essential cofactors for a wealth of biological processes, including oxidative phosphorylation, gene regulation and free-radical homeostasis. Failure to maintain appropriate levels of metal ions in humans is a feature of hereditary haemochromatosis, disorders of metal-ion deficiency, and certain neurodegenerative diseases. Despite their pivotal physiological roles, however, there is no molecular information on how metal ions are actively absorbed by mammalian cells. We have now identified a new metal-ion transporter in the rat, DCT1, which has an unusually broad substrate range that includes Fe2+, Zn2+, Mn2+, Co2+, Cd2+, Cu2+, Ni2+ and Pb2+. DCT1 mediates active transport that is proton-coupled and depends on the cell membrane potential. It is a 561-amino-acid protein with 12 putative membrane-spanning domains and is ubiquitously expressed, most notably in the proximal duodenum. DCT1 is upregulated by dietary iron deficiency, and may represent a key mediator of intestinal iron absorption. DCT1 is a member of the 'natural-resistance-associated macrophage protein' (Nramp) family and thus its properties provide insight into how these proteins confer resistance to pathogens.

The electrogenic Na/HCO3 cotransporter

The electrogenic Na/HCO3 cotransporter (symporter) is the major HCO3- transporter of the renal proximal tubule (PiT), located at the basolateral membrane (BLM), and also plays a noteworthy role in Na+ reabsorption. HCO3 transporters are important for regulation of intracellular pH (pHi) in most cells and also thereby regulate blood pH. This electrogenic Na/HCO3 cotransporter was first discovered using perfused Ambystoma tigrinum (salamander) renal, proximal tubules. This novel cotransporter mediates the movement of one Na+ ion with several HCO3- ions, making it electrogenic, is blocked by stilbene compounds, but does not depend on intra- or extracellular Cl-. This and similar cotransporters have been found in a number of tissues and cell types. Recently, we used Xenopus-laevis oocytes to expression clone the salamander renal electrogenic Na Bicarbonate Cotransporter (NBC). Using microelectrodes to monitor membrane potential (Vm) and intracellular pH (pHi), we followed oocyte expression after injecting poly (A)+, fractioned poly (A)+, or cRNA. All experimental solutions contained 100 microM ouabain to block the Na+/K+ pump. Our expression assay was to apply 1.5% CO2/10 mM HCO3- (pH 7.5), allow pHi to stabilize from the CO2-induced acidification, and then remove bath Na+. Removing bath Na+ from native oocytes and water-injected controls, hyperpolarized the oocytes by approximately 5 mV and had no effect on pHi. However, for oocytes injected with poly (A)+ RNA, removing Na+ transiently depolarized the cell by approximately 10 mV and caused pHi to decrease; both effects were blocked by 4,4'-diisothiocyano-2,2'-stilbenedisulfonate (DIDS) and required HCO3-. Electrophoretic fractionation of the poly (A)+ RNA, enriched the expression signal. From the optimal expression-fraction, we constructed a size-selected cDNA library in pSPORT1. Screening our Ambystoma library yielded a single clone (aNBC). We could detect expression 3 days after injection of NBC cRNA. In aNBC-expressing oocytes, adding CO2/HCO3-elicited a large (> 50mV) and rapid hyperpolarization, followed by a partial relaxation as pHi stabilized. Na+ removal in CO2/HCO3-depolarized the cell by > 40mV and decreased pHi, aNBC encodes a protein of 1035 amino acids with several putative membrane-spanning domains, and has a low level of amino-acid homology (approximately 30% to the AE family of Cl-HCO3 exchangers. aNBC is the first member of a new family of Na(+)-linked HCO3- transporters and, together with the AE family, defines a new superfamily of HCO3- transporters. Using aNBC to screen a rat-kidney cDNA library, we identified a full-length cDNA clone (rNBC), rNBC encodes a protein of 1035 amino acids, is 86% identical to aNBC, and can be functionally expressed in oocytes.

Expression cloning and characterization of a renal electrogenic Na+/HCO3- cotransporter

Bicarbonate transporters are the principal regulators of pH in animal cells, and play a vital role in acid-base movement in the stomach, pancreas, intestine, kidney, reproductive system and central nervous system. The functional family of HCO3- transporters includes Cl- -HCO3- exchangers, three Na+/HCO3- cotransporters, a K+/HCO3- cotransporter, and a Na+-driven Cl- -HCO3- exchanger. Molecular information is sparse on HCO3- transporters, apart from Cl- -HCO3- exchangers ('anion exchangers'), whose complementary DNAs were cloned several years ago. Attempts to clone other HCO3- transporters, based on binding of inhibitors, protein purification or homology with anion exchangers, have so far been unsuccessful. Here we monitor the intracellular pH and membrane voltage in Xenopus oocytes to follow the expression of the most electrogenic transporter known: the renal 1:3 electrogenic Na+/HCO3- cotransporter from the salamander Ambystoma tigrinum. We now report the successful cloning and characterization of a cDNA encoding a cation-coupled HCO3- transporter. The encoded protein is 1,035 amino acids long with several potential membrane-spanning domains. We show that when it is expressed in Xenopus oocytes, this protein is electrogenic, Na+ and HCO3- dependent, and blocked by the anion-transport inhibitor DIDS, and conclude that it is the renal electrogenic sodium bicarbonate cotransporter (NBC).

Symmetry of H+ binding to the intra- and extracellular side of the H+-coupled oligopeptide cotransporter PepT1

Ion-coupled solute transporters exhibit pre-steady-tate currents that resemble those of voltage-dependent ion channels. These currents were assumed to be mostly due to binding and dissociation of the coupling ion near the extracellular transporter surface. Little attention was given to analogous events that may occur at the intracellular surface. To address this issue, we performed voltage clamp studies of Xenopus oocytes expressing the intestinal H+-coupled peptide cotransporter PepT1 and recorded the dependence of transient charge movements in the absence of peptide substrate on changing intra- (pHi) and extracellular pH (pHo). Rapid steps in membrane potential induced transient charge movements that showed a marked dependence on pHi and pHo. At a pHo of 7.0 and a holding potential (Vh) of -50 mV, the charge movements were mostly inwardly directed, whereas reduction of pHo to below 7.0 resulted in outwardly directed charge movements. When pHi was reduced, inwardly directed charge movements were observed. The data on the voltage dependence of the transient charge movements were fitted by the Boltzmann equation, yielding an apparent valence of 0.65 +/- 0.03 (n = 7). The midpoint voltage (V0.5) of the charge distribution shifted linearly as a function of pHi and pHo. Our results indicate that, as a first approximation, the magnitude and polarity of the transient charge movements depend upon the prevailing H+ electrochemical gradient. We propose that PepT1 has a single proton binding site that is symmetrically accessible from both sides of the membrane and that decreasing the H+ chemical potential (DeltamuH) or increasing the membrane potential (Vm) shifts this binding site from an outwardly to an inwardly facing occluded state. This concept constitutes an important extension of previous kinetic models of ion-coupled solute transporters by including a more detailed description of intracellular events.

Stoichiometry and pH dependence of the rabbit proton-dependent oligopeptide transporter PepT1

1. The intestinal H(+)-coupled peptide transporter PepT1, displays a broad substrate specificity and accepts most charged and neutral di- and tripeptides. To study the proton-to-peptide stoichiometry and the dependence of the kinetic parameters on extracellular pH (pHo), rabbit PepT1 was expressed in Xenopus laevis oocytes and used for uptake studies of radiolabelled neutral and charged dipeptides, voltage-clamp analysis and intracellular pH measurements. 2. PepT1 did not display the substrate-gated anion conductances that have been found to be characteristic of members of the Na(+)- and H(+)-coupled high-affinity glutamate transporter family. In conjunction with previous data on the ion dependence of PepT1, it can therefore be concluded that peptide-evoked charge fluxes of PepT1 are entirely due to H+ movement. 3. Neutral, acidic and basic dipeptides induced intracellular acidification. The rate of acidification, the initial rates of the uptake of radiolabelled peptides and the associated charge fluxes gave proton-substrate coupling ratios of 1:1, 2:1 and 1:1 for neutral, acidic and basic dipeptides, respectively. 4. Maximal transport of the neutral and charged dipeptides Gly-Leu, Gly-Glu, Gly-Lys and Ala-Lys occurred at pHo 5.5, 5.2, 6.2 and 5.8, respectively. The Imax values were relatively pHo independent but the apparent affinity (Km(app) values for these peptides were shown to be highly pHo dependent. 5. Our data show that at physiological pH (pHo 5.5-6.0) PepT1 prefers neutral and acidic peptides. The shift in transport maximum for the acidic peptide Gly-Glu to a lower pH value suggests that acidic dipeptides are transported in the protonated form. The shift in the transport maxima of the basic dipeptides to higher pH values may involve titration of a side-chain on the transporter molecule (e.g. protonation of a histidine group). These considerations have led us to propose a model for coupled transport of neutral, acidic and basic dipeptides.

The renal electrogenic Na+:HCO-3 cotransporter

The electrogenic Na+:HCO3- cotransporter (symporter) is the major transporter for HCO3- reabsorption across the basolateral membrane of the renal proximal tubule and also contributes significantly to Na+ reabsorption. We expression-cloned the salamander renal electrogenic Na+:Bicarbonate Cotransporter (NBC) in Xenopus laevis oocytes. After injecting poly(A)+ RNA, fractionated poly(A)+ RNA or cRNA, we used microelectrodes to monitor membrane potential (Vm) and intracellular pH (pHi) All solutions contained ouabain to block the Na+/K+ pump (P-ATPase). After applying 1.5% CO2/10 mmol l-1 HCO3- (pH 7.5) and allowing pHi to stabilize from the CO2-induced acidification, we removed Na+. In native oocytes or water-injected controls, removing Na+ hyperpolarized the cell by -5 mV and had no effect on pHi. In oocytes injected with poly(A)+ RNA, removing Na+ transiently depolarized the cell by -10 mV and caused pHi to decrease; both effects were blocked by 4,4'-diisothiocyano-2,2'-stilbenedisulfonate (DIDS) and required HCO3-. We enriched the signal by electrophoretic fractionation of the poly(A)+ RNA, and constructed a size-selected cDNA library in pSPORT1 using the optimal fraction. Screening the Ambystoma library yielded a single clone (aNBC). Expression was first obvious 3 days after injection of NBC cRNA. Adding CO2/HCO3- induced a large (&gt; 50 mV) and rapid hyperpolarization, followed by a partial relaxation as pHi stabilized. Subsequent Na+ removal depolarized the cell by more than 40 mV and decreased pHi. aNBC is a full-length clone with a start Met and a poly(A)+ tail; it encodes a protein with 1025 amino acids and several putative membrane-spanning domains. aNBC is the first member of a new family of Na(+)-linked HCO3- transporters. We used aNBC to screen a rat kidney cDNA library, and identified a full-length cDNA clone (rNBC) that encodes a protein of 1035 amino acids. rNBC is 86% identical to aNBC and can be functionally expressed in oocytes.

Electrogenic properties of the epithelial and neuronal high affinity glutamate transporter

Active ion-coupled glutamate transport is of critical importance for excitatory synaptic transmission, normal cellular function, and epithelial amino acid metabolism. We previously reported the cloning of the rabbit intestinal high affinity glutamate transporter EAAC1 (Kanai, Y., and Hediger, M. A. (1992) Nature 360, 467-471), which is expressed in numerous tissues including intestine, kidney, liver, heart, and brain. Here, we report a detailed stoichiometric and kinetic analysis of EAAC1 expressed in Xenopus laevis oocytes. Uptake studies of 22Na+ and [14C]glutamate, in combination with measurements of intracellular pH with pH microelectrodes gave a glutamate to charge ratio of 1:1, a glutamate to Na+ ratio of 1:2, and a OH-/H+ to charge ratio of 1:1. Since transport is K+ dependent it can be concluded that EAAC1-mediated glutamate transport is coupled to the cotransport of 2 Na+ ions, the countertransport of one K+ ion and either the countertransport of one OH- ion or the cotransport of 1 H+ ion. We further demonstrate that under conditions where the electrochemical gradients for these ions are disrupted, EAAC1 runs in reverse, a transport mode which is of pathologic importance. 22Na+ uptake studies revealed that there is a low level of Na+ uptake in the absence of extracellular glutamate which appears to be analogous to the Na+ leak observed for the intestinal Na+/glucose cotransporter SGLT1. In voltage clamp studies, reducing extracellular Na+ from 100 to 10 mM strongly increased K0.5L-glutamate and decreased I(max). The data indicate that Na+ binding at the extracellular transporter surface becomes rate-limiting. Studies addressing the cooperativity of the substrate-binding sites indicate that there are two distinct Na(+)-binding sites with different affinities and that Na+ binding is modulated by extracellular glutamate. A hypothetical ordered kinetic transport model for EAAC1 is discussed.

Characterization of paracellular permeability in cultured human cervical epithelium: regulation by extracellular adenosine triphosphate

OBJECTIVE

The purpose of the present study was to compare the permeability and regulation of paracellular transport in human cervical cells with those in epithelial cells of other organs.

METHODS

Cervical cells (ECE16-1, Caski, and HT3) were grown on filters, and transepithelial electrical conductance (GT) and the permeability to pyranine (PPyr) were determined.

RESULTS

Cervical cultures were characterized by high GT (83-125 mS.cm-2) and high PPyr (6.2-18 x 10(-6).sec-1). The GT was not significantly affected by cell density but was increased by 20% by lowering extracellular calcium to 0.45 mmol/L or less. The high values of GT and PPyr and the regulation by extracellular calcium indicate that all three cervical cell lines have "leaky" tight junctional complexes. Addition of extracellular adenosine triphosphate (ATP) at 50 mumol/L to the cervical cultures evoked a biphasic change in GT that was unique to the cervical cells: an initial increase, followed by a sustained decrease by 30% from baseline GT. The decrease of GT was associated with a decrease in PPyr by 17%, indicating that ATP had an effect on the tight junctional/paracellular permeability. The ATP effect was reversible either by washing or by chemical hydrolysis with ATPase. The non-cervical cell lines all responded to extracellular ATP with a transient increase in GT, but not with the pronounced decrease.

CONCLUSION

The permeability of the paracellular pathway can be regulated in cervical epithelia by mechanisms that may be different from those in epithelial cells from other organs.

ATP decreases acutely and reversibly transport through the paracellular pathway in human cervical cells

We studied the effect of ATP on transepithelial transport through the paracellular pathway in human cervical cells. Transepithelial conductance and transepithelial permeability (determined from the measurements of unidirectional flux of inert molecules) were measured in Caski cells grown on permeable support. Transepithelial conductance was 55.9 +/- 17.7 mS/cm2 and permeability was 12.5 +/- 2.7 x 10(-6) cm/s for a 0.51-kDa probe. Addition of ATP to the medium decreased acutely and reversibly the conductance and the permeability to probes between 0.18 and 10 kDa by 23-31% in a dose-related fashion; the 50% effective concentration was 1 microM, with a maximal effect at 5-10 microM extracellular ATP. The ATP effect was observed regardless of the pressure gradient across the epithelium. These results indicate that extracellular ATP in micromolar concentrations decreases acutely and reversibly the permeability through the paracellular pathway in cervical cells, possibly by affecting the permeability of the tight junctions and the resistance of the intercellular space. On the basis of these data, we speculate that ATP may play a role in the regulation of solutes and fluid transport across the cervical epithelium in vivo.

Expression cloning of a mammalian proton-coupled oligopeptide transporter

In mammals, active transport of organic solutes across plasma membranes was thought to be primarily driven by the Na+ gradient. Here we report the cloning and functional characterization of a H(+)-coupled transporter of oligopeptides and peptide-derived antibiotics from rabbit small intestine. This new protein, named PepT1, displays an unusually broad substrate specificity. PepT1-mediated uptake is electrogenic, independent of extracellular Na+, K+ and Cl-, and of membrane potential. PepT1 messenger RNA was found in intestine, kidney and liver and in small amounts in brain. In the intestine, the PepT1 pathway constitutes a major mechanism for absorption of the products of protein digestion. To our knowledge, the PepT1 primary structure is the first reported for a proton-coupled organic solute transporter in vertebrates and represents an interesting evolutionary link between prokaryotic H(+)-coupled and vertebrate Na(+)-coupled transporters of organic solutes.

Human uterine cervical epithelial cells grown on permeable support--a new model for the study of differentiation

The purpose of the present study was to establish culture conditions for human uterine cervical epithelial cells on permeable support and to determine how it affects cervical cell differentiation. Human ectocervical epithelial cells (hECE), HPV-16 immortalized hECE cells (ECE16-1) and Caski cells were grown on collagen-coated filters. Culture conditions, density of cells in culture and expression of epithelial and cervical-cell phenotypic markers were determined and compared in cells grown on filter and on solid support. Compared with the latter, cultures on filter had a higher cell density, hECE cells stratified to 5-12 cell layers compared to 1-3 on solid support, and cells of all three types expressed intercellular tight junctions. The cytokeratin profiles revealed differences between the three cell types as well as differences within the same cell species when grown on filter, compared to solid support. Of particular importance was the finding of a higher expression of K-13 in hECE grown on filter compared to solid support; K-13 is a marker of ectocervical cell differentiation. The cytokeratin profiles of the cultured hECE, ECE16-1 and Caski cells resembled those of ectocervical, squamous metaplastic and endocervical epithelia, respectively. hECE and ECE16-1 expressed involucrin protein, the level of which in both was higher in cells grown on filter compared to solid support. Polarization of the cultures was determined by morphology (stratification of hECE cells, expression of pseudomicrovilli in the apical cell membrane), selective apical vs. basolateral secretion of [35S]methionine- and [35S]cysteine-, [3H]fucose- and [14C]glucosamine-labeled molecules, and positive short-circuit current (Isc) under voltage-clamp conditions. Confluency of the cultures was determined by measuring transepithelial unidirectional fluxes of inert molecules with different molecular weights (MWs) through the paracellular pathway, and by measuring transepithelial conductance. The results indicated transepithelial permeability of 7-22.10(-6) cm.sec-1, which was 5-100 fold smaller compared to blank inserts, with a cut-off MW of 40-70 kDa for hECE and Caski cells. Transepithelial conductance ranged 18.5 to 51.5 mS.cm-2, indicating a leaky but confluent epithelia. Collectively the results indicate the epithelial nature of the cells and their improved differentiation when grown on filter support; hECE is a model for ectocervical epithelium while ECE16-1 and Caski express phenotypic characteristics of squamous metaplastic cervical epithelium and endocervical epithelium respectively.

Modulation of phospholipase A2 activity and sodium transport by angiotensin-(1-7)

Angiotensin II (Ang II) receptors are coupled to a variety of signal transduction mechanisms. In the kidney, Ang II at nanomolar concentration binds to proximal tubular cells and stimulates phospholipase A2 (PLA2), which in turn catalyzes the hydrolysis of phosphatidylcholine into lysophosphatidylcholine (LPC) and fatty acid. This signal transduction pathway has been shown to be an important modulator of sodium transport. The kidney cortex possesses the enzyme necessary to convert angiotensin I (Ang I) directly to Ang-(1-7) bypassing Ang II as an intermediate. The present investigation was undertaken to determine whether Ang-(1-7) influences epithelial cell function by comparing this heptapeptide with Ang II as a modulator of PLA2 activity and sodium transport. Proximal tubular cells were labeled in tissue culture with 3H-choline and PLA2 activity was measured by quantitation of LPC. We found that Ang II (10(-9) M to 10(-6) M) significantly increased PLA2 activity (154 +/- 36% to 209 +/- 94%). Similar results were obtained with Ang-(1-7) (240 +/- 130% to 353 +/- 40%). The bioactivity of the peptides was assayed by its ability to regulate transcellular 22Na flux. Ang II (10(-9) M) inhibited 22Na flux by 12 +/- 2% while Ang-(1-7) (10(-9) M) inhibited 22Na flux by 20 +/- 5%. These results suggest that one potential role of Ang-(1-7) in the regulation of kidney epithelial electrolyte transport may involve activation of PLA2.

Development and characterization of rabbit proximal tubular epithelial cell lines

We have isolated rabbit kidney proximal tubular epithelial cell lines. The selection was based on their ability to form confluent monolayers on porous supports and to maintain receptor-mediated signal transduction and ion transport, characteristic of the proximal tubule. The isolation method consisted of several steps: (1) superficial cortical proximal tubule segments were microdissected and cultured on a matrix-coated porous support until cells formed a confluent monolayer; (2) primary cultures showing hormone-regulated ion transport typical for the proximal tubule were selected and co-cultured with irradiated fibroblasts; and (3) the epithelial cells surviving after several passages were expanded and passaged on porous substrates. Most of the cell lines developed in this manner were obtained by co-culture with irradiated fibroblasts producing a recombinant retrovirus encoding SV40 large T antigen and G418 resistance. However, SV40 T antigen expression was not essential for immortalization, since neither T antigen nor G418 resistance was detected in the isolated cell lines and co-culture with non-producing 3T3 cells gave similar results. One cell line (vEPT) has been characterized in some detail with respect to morphological, biochemical, and ion transport properties. This line forms confluent monolayers with apical microvilli, tight junctions, and convolutions of the basolateral plasma membrane. Once confluent, monolayers maintain conductances of 25 to 32 mS/cm2 for several weeks in culture and possess phlorizin-sensitive short-circuit current (Isc) in glucose containing media, indicative of apical Na(+)-glucose co-transport. vEPT cells also retain receptor and signaling mechanisms for angiotensin II (Ang II). Apical and basal Ang II and 5,6-epoxy-eicosatrienoic acid (5,6-EET) modulate the Isc in a manner similar to primary cultures. The cell lines share with primary cultures expression of the cytokeratins K8, K10/K11, and K19 ("nomenclature" [21]). They also retain several receptor and signal transduction mechanisms. For example, Ang II, arachidonate, bradykinin, 5,6-EET, parathyroid hormone (residues 1 through 34), and purine nucleotides increase cytosolic Ca2+, PTH elevates cAMP levels, and Ang II enhances proximal tubule-specific arachidonic acid metabolism.

Angiotensin II actions in the rabbit proximal tubule. Angiotensin II mediated signaling mechanisms and electrolyte transport in the rabbit proximal tubule

Angiotensin II (AngII) is a potent regulator of electrolyte transport with biphasic effects on salt and HCO3-resorption in proximal tubule epithelia (PCT). In cultured PCT cells, pM to nM AngII activates a GTP-binding protein to inhibit cAMP formation and thus releases inhibition of apical Na/H exchange. Phospholipase A2 is activated by nM to microM AngII releasing arachidonate which is metabolized by a novel P450 epoxygenase to form 5,6-epoxy-eicosatrienoic acid (5,6-EET). 5,6-EET and nM apical AngII cause dihydropyridine-sensitive Ca2+ influx from the extracellular space, inhibition of apical-to-basolateral Na flux, and decrease in epithelial monolayer short circuit current. 5,6-EET also inhibits Na/K-ATPase by 50%. This P450 epoxygenase is physiologically important in the AngII-signaling system because the P450 inhibitor ketoconazole blocks AngII effects while potentiating exogenous 5,6-EET effects. Finally, these AngII-mediated signaling systems are polarized in the PCT with pM basolateral AngII inhibiting adenylate cyclase and nM apical AngII activating PLA2 and subsequent generation of 5,6-EET.