Distribution of the vacuolar H+ atpase along the rat and human male reproductive tract

Luminal acidification in parts of the male reproductive tract generates an appropriate pH environment in which spermatozoa mature and are stored. The cellular mechanisms of proton (H+) secretion in the epididymis and the proximal vas deferens involve the activity of an apical vacuolar H+ ATPase in specialized cell types, as well as an apical Na+/H+ exchanger in some tubule segments. In this study we used Western blotting and immunocytochemistry to localize the H+ ATPase in various segments of the male reproductive tract in rat and man as a first step toward a more complete understanding of luminal acidification processes in this complex system of tissues. Immunoblotting of isolated total cell membranes indicated a variable amount of H+ ATPase in various segments of the rat reproductive tract. In addition to its known expression in distinct cell types in the epididymis and vas deferens, the H+ ATPase was also localized at the apical pole and in the cytoplasm of epithelial cells in the efferent duct (nonciliated cells), the ampulla of the vas deferens and the ventral prostate (scattered individual cells), the dorsal and lateral prostate, the ampullary gland, the coagulating gland, and all epithelial cells of the prostatic and penile urethra. Both apical and basolateral localization of the protein were found in epithelial cells of the prostatic ducts in the lateral prostate and in periurethral tissue. Only cytoplasmic, mostly perinuclear localization of the H+ ATPase was found in all epithelial cells of the seminal vesicles and in most cells of the ventral prostate and coagulating gland. No staining was detected in the seminiferous tubules, rete testis, and bulbourethral gland. In human tissue, H+ ATPase-rich cells were detected in the epididymis, prostate, and prostatic urethra. We conclude that the vacuolar H+ ATPase is highly expressed in epithelial cells of most segments of the male reproductive tract in rat and man, where it may be involved in H+ secretion and/or intracellular processing of the material endocytosed from the luminal fluid or destined to be secreted by exocytosis.

Submitochondrial distribution and delayed proteolysis of subunit c of the H+-transporting ATP-synthase in ovine ceroid-lipofuscinosis

The neuronal ceroid-lipofuscinose (NCL) are recessively inherited lysosomal storage diseases in children and animals. The major stored protein in many of these diseases is subunit c of the mitochondrial inner membrane H+-transporting ATP-synthase. Previous studies of naturally occurring ovine ceroid-lipofuscinosis (OCL) in South Hampshire sheep showed that the genes and transcripts for subunit c were normal and inferred that this protein was expressed normally in mitochondria prior to storage in lysosomes. Accumulation in mitochondria has not been conclusively established and we have therefore used the South Hampshire model to demonstrate approximately 1.8-fold normal levels of subunit c in mitochondrial inner membranes prepared from liver. Other mitochondrial inner membrane and ATP-synthase proteins that could be detected by mass spectrometry (MS) or two-dimensional electrophoresis (2-DE) were present in normal amounts. The accumulating subunit c showed normal post-translational modification but was abnormally resistant to proteolysis. These results are consistent with the hypothesis that OCL may result from a mitochondrial disorder that affects turnover of correctly expressed subunit c, although we cannot exclude the possibility that a postmitochondrial defect delays processing of subunit c out of mitochondria.

Immunolocalization of plasma-membrane H+-ATPase and tonoplast-type pyrophosphatase in the plasma membrane of the sieve element-companion cell complex in the stem of Ricinus communis L

Plasma-membrane-located primary pumps were investigated in the sieve element (SE)-companion cell complex in the transport phloem of 2-week-old stems of Ricinus communis L. and, for comparison, in stems of Cucurbita pepo L. and in the secondary phloem of Agrobacterium tumefaciens-induced crown galls as a typical sink tissue. The plasma-membrane (PM) H+-ATPase and the tonoplast-type pyrophosphatase (PPase) were immunolocalized by epifluorescence and confocal laser scanning microscopy (CLSM) upon single or double labeling with specific monoclonal and polyclonal antibodies. Quantitative fluorescence evaluation by CLSM revealed both pumps in one membrane, the sieve-element PM. Different PM H+-ATPase antibody clones, raised against the PM H+-ATPase of Zea mays coleoptiles, induced in mouse and produced in mouse hybridoma cells, discriminated between different phloem cell types. Clones 30D5C4 and 44B8A1 labeled sieve elements and clone 46E5B11D5 labeled companion cells, indicating the existence of different phloem PM H+-ATPase isoforms. The results are discussed in terms of energization of SE transporters for retrieval of leaking sucrose, K+ and amino acids, as one of the unknown roles of ATP found in SEs. The function of the PPase could be related to phloem sucrose metabolism in support of ATP-requiring processes.

Equine neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinosis (NCL) is an inherited, neurodegenerative disorder with fatal outcome in humans. It has also been described in some animal species; this is the first report of NCL in equines. Three horses showed developmental retardation, slow movements and loss of appetite at the age of six months. Neurological symptoms, as well as visual failure in one case, were noticed at the age of 1 year. Due to slowly progressing deterioration, euthanasia was indicated 1.5 years after onset of conspicuous behavior. At necropsy, slight flattening of the gyri and discoloring of the brain was noticed. Histopathology revealed eosinophilic, autofluorescent material in the perikarya of neurons throughout the brain and spinal cord. Identical material was found in neurons of retina, submucous and myenteric ganglia, as well as in glial cells. Immunohistochemistry, using antiserum against subunit c of mitochondrial ATP synthase, showed positive signals in neurons and glial cells. Electron microscopical studies revealed fingerprint profiles mixed with rectilinear structures in markedly enlarged lysosomes of neurons and renal tubules, and rectilinear structures mixed with curvilinear bodies in macrophages and lymphocytes of lymph nodes. Thus, our study presents the first occurrence of lysosomal storage disease in horses, further characterized by immunohistochemical and electron microscopical investigations as NCL.

Morphological studies on CLN2

Electron microscopic, fluorescence microscopic, and immunohistochemical studies earlier performed on archival cerebral tissue from Max Bielchowsky's original three patients revealed curvilinear bodies rich in subunit C of mitochondrial ATP synthase (SCMAS). Recent progress in the elucidation of CLN2, i.e. identification of the defective lysosomal enzyme tripeptidyl-peptidase I (TPP-I) and mutations in the CLN2 gene have further corroborated earlier data. Immunohistochemically the absence of the TPP-I protein could be confirmed in the archival tissues using pathological controls. Unlike biochemistry, immunohistochemistry enables examination of these archival tissues elucidating the causative defect. Complementary molecular studies identified mutations in the CLN2 gene in the archival tissues and thereby convincingly demonstrated that these three children truly had classic late infantile neuronal ceroid lipofuscinosis (LINCL), now called CLN2. This archival study documents the possibilities to revalidate disease-specific original nosologic reports. Chloroquine is toxic to lysosomal enzymes and results in lysosomal storage. The material is autofluorescent and gives the ultrastructural pattern of curvilinear profiles, thus resembling classic late infantile NCL, representing a good experimental model. In humans chloroquine therapy may cause a myopathy (and retinopathy) and, as recently suggested, an encephalopathy marked by lysosomal accretion in several cell types including neurons. Immunohistochemically, SCMAS also accumulates, further strengthening morphologic similarity between LINCL and human chloroquine intoxication.

Effects of brefeldin-A: Potent inhibitor of intracellular protein transport on ultrastructure and resorptive function of cultured osteoclasts

Brefeldin-A (BFA) is a specific and potent inhibitor of the intracellular transport of clathlin-uncoated transitional vesicles from the cisterns of rough-surfaced endoplasmic reticulum (RER) to the Golgi lamellae. This study was designed to clarify the effects of BFA on ultrastructure, subcellular localization of vacuolar-type H+-ATPase and a lysosomal cysteine proteinase, cathepsin K, in cultured osteoclasts and their resorptive function. H+-ATPase and cathepsin K are the most important enzymes for decalcification of apatite crystals and degradation of type-I collagen, respectively. In control cultures without BFA, osteoclasts were structurally characterized by the development of broad ruffled borders and clear zones, and formed many resorption lacunae in cocultured dentine slices. In BFA-treated cultures, osteoclasts lacked ruffled borders, and the cytoplasm was filled with regular-size and extremely large pale vacuoles over 2 microm in diameter, which were produced by fusion of adjacent vacuoles. BFA did not, however, inhibit clear zone formation and adhesion of osteoclasts to dentine slices. Resorption lacuna formation was markedly diminished by BFA treatment. Although H+-ATPase and cathepsin K were strongly expressed in osteoclast ruffled borders in control cultures, BFA treatment altered the subcellular localization and decreased the expression of these molecules. In BFA-treated cultures, H+-ATPase immunoreaction in osteoclasts was observed along the limiting membranes of some, but not all, regular-size pale vacuoles, but neither in extremely large vacuoles nor along the smooth plasma membranes facing the dentine slices. Similarly, cathepsin K was localized within lysosomes and some regular-size pale vacuoles, but its secretion toward the dentine slices through the ruffled borders was strongly inhibited by BFA treatment. These results suggest that 1.) formation of the osteoclast ruffled borders and their resorptive function are closely associated with the intracellular transport of these molecules from the RER cisterns and the Golgi lamellae to the ruffled borders, and 2.) both H+-ATPase and cathepsin K are selectively transported to the ruffled border membranes by pale vacuoles.

Immunohistochemical localization of V-ATPases in rat spermatids

The sperm acrosome exhibits a low pH. However, the mechanism of acidification in the acrosome remains unclear. Vacuolar-type proton ATPase (V-ATPase) has been shown to play a principle role in generating and maintaining the acidity of organelles such as lysosomes and endosomes. In this study, we examined whether V-ATPase is localized in the acrosome membranes using immunohistochemical techniques. Sections of rat testis were immunostained using antibodies against V-ATPase. Under light microscopic observation, the perinuclear region in spermatids at an early stage of development was heavily immunostained. At the electron microscopic level, gold particles showing the presence of V-ATPase were localized to the acrosome membranes in the developing spermatids. V-ATPase was also localized to the membrane of vesicles locating between the trans-Golgi area and the acrosome. These observations suggest that V-ATPase may play a role in acrosome acidification.

Differential activation of H+-ATPase genes by an arbuscular mycorrhizal fungus in root cells of transgenic tobacco

In arbuscular mycorrhizas, H+-ATPase is active in the plant membrane around arbuscules but absent from plant mutants defective in arbuscule development (Gianinazzi-Pearson et al. 1995, Can J Bot 73: S526-S532). The proton-pumping H+-ATPase is encoded by a family of genes in plants. Immunocytochemical studies and promoter-gusA fusion assays were performed in transgenic tobacco (Nicotiana tabacum L.) to determine whether the periarbuscular enzyme activity results from de-novo activation of plant genes by an arbuscular mycorrhizal fungus. The H+-ATPase protein was localized in the plant membrane around arbuscule hyphae. The enzyme was absent from non-colonized cortical cells. Regulation of seven H+-ATPase genes (pma) was compared in non-mycorrhizal and mycorrhizal roots by histochemical detection of beta-glucuronidase (GUS) activity. Two genes (pma2, pma4) were induced in arbuscule-containing cells of mycorrhizal roots but not in non-mycorrhizal cortical tissues or senescent mycorrhiza. It is concluded that de-novo H+-ATPase activity in the periarbuscular membrane results from selective induction of two H+-ATPase genes, which can have diverse roles in plant-fungal interactions at the symbiotic interface.

Characterization of isolated acidocalcisomes of Trypanosoma cruzi

The acidocalcisome is an acidic calcium store in trypanosomatids with a vacuolar-type proton-pumping pyrophosphatase (V-H(+)-PPase) located in its membrane. In this paper, we describe a new method using iodixanol density gradients for purification of the acidocalcisome from Trypanosoma cruzi epimastigotes. Pyrophosphatase assays indicated that the isolated organelle was at least 60-fold purified compared with the large organelle (10,000 x g) fraction. Assays for other organelles generally indicated no enrichment in the acidocalcisome fraction; glycosomes were concentrated 5-fold. Vanadate-sensitive ATP-driven Ca(2+) uptake (Ca(2+)-ATPase) activity was detectable in the isolated acidocalcisome, but ionophore experiments indicated that it was not acidic. However, when pyrophosphate was added, the organelle acidified, and the rate of Ca(2+) uptake increased. Use of the indicator Oxonol VI showed that V-H(+)-PPase activity generated a membrane potential. Use of sulfate or nitrate in place of chloride in the assay buffer did not affect V-H(+)-PPase activity, but there was less activity with gluconate. Organelle acidification was countered by the chloride/proton symport cycloprogidiosin. No vacuolar H(+)-ATPase activity was detectable in isolated acidocalcisomes. However, immunoblots showed the presence of at least a membrane-bound V-H(+)-ATPase subunit, while experiments employing permeabilized epimastigotes suggested that vacuolar H(+)-ATPase and V-H(+)-PPase activities are present in the same Ca(2+)-containing compartment.

Molecular characterization of the yeast vacuolar H+-ATPase proton pore

The Saccharomyces cerevisiae vacuolar ATPase (V-ATPase) is composed of at least 13 polypeptides organized into two distinct domains, V(1) and V(0), that are structurally and mechanistically similar to the F(1)-F(0) domains of the F-type ATP synthases. The peripheral V(1) domain is responsible for ATP hydrolysis and is coupled to the mechanism of proton translocation. The integral V(0) domain is responsible for the translocation of protons across the membrane and is composed of five different polypeptides. Unlike the F(0) domain of the F-type ATP synthase, which contains 12 copies of a single 8-kDa proteolipid, the V-ATPase V(0) domain contains three proteolipid species, Vma3p, Vma11p, and Vma16p, with each proteolipid contributing to the mechanism of proton translocation (Hirata, R., Graham, L. A., Takatsuki, A., Stevens, T. H., and Anraku, Y. (1997) J. Biol. Chem. 272, 4795-4803). Experiments with hemagglutinin- and c-Myc epitope-tagged copies of the proteolipids revealed that each V(0) complex contains all three species of proteolipid with only one copy each of Vma11p and Vma16p but multiple copies of Vma3p. Since the proteolipids of the V(0) complex are predicted to possess four membrane-spanning alpha-helices, twice as many as a single F-ATPase proteolipid subunit, only six V-ATPase proteolipids would be required to form a hexameric ring-like structure similar to the F(0) domain. Therefore, each V(0) complex will likely be composed of four copies of the Vma3p proteolipid in addition to Vma11p and Vma16p. Structural differences within the membrane-spanning domains of both V(0) and F(0) may account for the unique properties of the ATP-hydrolyzing V-ATPase compared with the ATP-generating F-type ATP synthase.

Cadmium inhibits vacuolar H(+)ATPase-mediated acidification in the rat epididymis

In rats, an acidic luminal pH maintains sperm quiescence during storage in the epididymis. We recently showed that vacuolar H(+)ATPase-rich cells in the epididymis and vas deferens are involved in the acidification of these segments. Treatment of rats with cadmium (Cd) leads to alkalinization of this fluid by an unknown mechanism. Because Cd may affect H(+)ATPase function, we examined 1) the in vivo effect of Cd poisoning on H(+)ATPase-rich cell morphology and on the abundance and distribution of the 31-kDa H(+)ATPase subunit in cells along the rat epididymis, and 2) the in vitro effect of Cd on H(+)ATPase activity and function in the isolated vas deferens. Immunofluorescence and immunoblotting data from rats treated with Cd for 14-15 days (2 mg Cd/kg body mass/day) showed that 1) H(+)ATPase-positive cells regressed to a prepubertal phenotype, and 2) H(+)ATPase was lost from the apical pole of the cell and was redistributed into an intracellular compartment. In experiments in vitro, Cd inhibited bafilomycin-sensitive ATPase activity in isolated total cell membranes and, as measured using a proton-selective extracellular microelectrode, inhibited proton secretion in isolated vas deferens. We conclude that alkalinization of the tubule fluid in the epididymis and vas deferens of Cd-treated rats may result from the loss of functional H(+)ATPase enzyme in the cell apical domain as well as from a direct inhibition of H(+)ATPase function by Cd.

Selective localization of Bcl-2 to the inner mitochondrial and smooth endoplasmic reticulum membranes in mammalian cells

Bcl-2, an anti-apoptotic protein, is believed to be localized in the outer mitochondrial membrane, endoplasmic reticulum, and nuclear envelope. However, Bcl-2 has also been suggested as playing a role in the maintenance of mitochondrial membrane potential, indicating its possible association with the inner mitochondrial membrane. We therefore further examined the exact localization of Bcl-2 in mitochondria purified from wild-type and bcl-2-transfected PC12 cells and pre- and postnatal rat brains. Double immunostaining demonstrated that Bcl-2 was co-localized with subunit beta of F1F0ATPase in the inner mitochondrial membrane. Biochemical analysis of isolated mitochondria using digitonin and trypsin suggests an association of Bcl-2 with the inner mitochondrial membrane. More interestingly, the majority of Bcl-2 disappeared from the inner membrane of mitochondria when cultured under serum deprivation. These results suggest that Bcl-2 acts as an anti-apoptotic regulator by localizing mainly to the inner mitochondrial and smooth ER membranes.

The B1 subunit of the H+ATPase is a PDZ domain-binding protein. Colocalization with NHE-RF in renal B-intercalated cells

The 56-kDa B1 subunit of the vacuolar H(+)ATPase has a C-terminal DTAL amino acid motif typical of PDZ-binding proteins that associate with the PDZ protein, NHE-RF (Na(+)/H(+) exchanger regulatory factor). This B1 isoform is amplified in renal intercalated cells, which play a role in distal urinary acid-base transport. In contrast, proximal tubules express the B2 isoform that lacks the C-terminal PDZ-binding motif. Both the B1 56-kDa subunit and the 31-kDa (E) subunit of the H(+)ATPase are pulled down by glutathione S-transferase NHE-RF bound to GSH-Sepharose beads. These subunits associate in vivo as part of the cytoplasmic V1 portion of the H(+)ATPase, and the E subunit was co-immunoprecipitated from rat kidney cytosol with NHE-RF antibodies. The interaction of H(+)ATPase subunits with NHE-RF was inhibited by a peptide derived from the C terminus of the B1 but not the B2 isoform. NHE-RF colocalized with H(+)ATPase in either the apical or the basolateral region of B-type intercalated cells, whereas NHE-RF staining was undetectable in A-intercalated cells. In proximal tubules, NHE-RF was located in the apical brush border. In contrast, H(+)ATPase was concentrated in a distinct membrane domain at the base of the brush border, from which NHE-RF was absent, consistent with the expression of the truncated B2 subunit isoform in this tubule segment. The colocalization of NHE-RF and H(+)ATPase in B- but not A-intercalated cells suggests a role in generating, maintaining, or modulating the variable H(+)ATPase polarity that characterizes the B-cell phenotype.

V-Type H+-ATPase/synthase from a thermophilic eubacterium, Thermus thermophilus. Subunit structure and operon

V-type ATPase (V(o)V(1)) capable of ATP-driven H(+) pumping and of H(+) gradient driven ATP synthesis was isolated from a thermophilic eubacterium, Thermus thermophilus. When the enzyme was analyzed by gel electrophoresis in the presence of sodium dodecyl sulfate, it showed eight polypeptide bands of which four were subunits of V(1). We also isolated the V(o)V(1) operon, containing nine genes in the order of atpG-I-L-E-X-F-A-B-D, which encoded proteins with molecular sizes of 13, 43, 10, 20, 35, 11, 64, 53, and 25 kDa, respectively. The last four genes were identified as those for V(1) subunits; atpA, B, D, and F encoded the A, B, gamma, and delta subunits, respectively. The first five genes, atpG-atpX, were identified as genes for the V(o) subunits. The product of atpL, the proteolipid subunit, lacked a 19-amino acid presequence and, unlike V-type ATPases, contained two membrane-spanning domains rather than four. The hydrophobic 43-kDa product of atpI is the smallest member so far found of the eukaryotic 100-kDa subunit family. Its electrophoretic band overlapped with the band of the A subunit. Therefore, all the gene products were found in our purified V(o)V(1). We isolated the A(3)B(3) subcomplex reconstituted from the isolated subunits and the A(3)B(3)gamma subcomplex from subunit-expressing Escherichia coli. Electron microscopic observation of these subcomplexes revealed that the gamma subunit of V(1) filled the central cavity of A(3)B(3) and might be central subunit, similar to the gamma subunit of F(1)-ATPase.

Immunolocalization of CA II and H+ V-ATPase in epithelial cells of the mouse and rat epididymis

Acidification of the epididymal lumen has been suggested to play an important role in sperm functions; however, the cell types, pumps, and mechanisms involved have not been fully addressed. In this study, carbonic anhydrase II (CA II) and a 67-kd subunit of Neurospora crassa vacuolar proton adenosinetriphosphatase (H+ V-ATPase) pump were immunolocalized using light microscopy and electron microscopy (EM) in the epididymis of rats and mice. In both animals, narrow cells, identified in the initial segment and intermediate zone of the epididymis, contained numerous small vesicles in their apical region, often cup-shaped in appearance. In the mouse but not rat, these cells also possessed numerous cisternae of smooth endoplasmic reticulum, suggesting steroid synthesis; and cytoplasmic blebs of their apical cell surface, which appeared to detach, suggesting apocrine secretion. Anti-CA II antibody was immunocytochemically localized in the light microscope within narrow cells but not over any other cell types of the entire epididymis. Anti-H+ V-ATPase antibody was also localized in narrow cells of the initial segment and intermediate zone; as well as clear cells of the caput, corpus, and cauda regions. Using EM, gold particles for anti-CA II and H+ V-ATPase antibodies were noted in the apical region of narrow cells in relation to the numerous, small, cup-shaped vesicles. Although CA II was mainly located in the cytosol near these vesicles, H+ V-ATPase appeared on their delimiting membrane and on the apical plasma membrane of these cells. A similar distribution was noted for H+ V-ATPase in clear cells. The nature of the small vesicles of the apical region of narrow cells was examined with electron-dense fluid phase tracers that were introduced into the epididymal lumen. The tracers appeared within these vesicles and a few endosomes 1 hour after injection, suggesting that they contact the apical plasma membrane. Since these vesicles are also related to CA II and H+ V-ATPase, the data suggests that, as the site of proton production, the vesicles recycle to and from the apical cell surface, and in this way, deliver protons to the epididymal lumen for acidification. Clear cells and their expression of H+ V-ATPase may also serve in this function. In summary, both narrow and clear cells appear to be involved in luminal acidification, an activity that may be essential for sperm as they traverse and are stored in the epididymis.

Mitochondrial ATP synthase 6 as an endogenous control in the quantitative RT-PCR analysis of clinical cancer samples

BACKGROUND

Real-time polymerase chain reaction (PCR) is a powerful new technique in the evolution of quantitative reverse transcription-PCR assays. With the increased sensitivity and resolution of real-time techniques, the requirements for constitutive expression of endogenous controls have become increasingly stringent.

METHODS AND RESULTS

We compare the expression of the mitochondrial gene, adenosine triphosphate synthase 6 (ATPsy6), to the expression of other routinely used endogenous control genes (e.g., beta-actin, glyceraldehyde-3-phosphate dehydrogenase [GAPDH], ribosomal RNA 18S [18S rRNA], and cyclophilin). In a diverse assortment of tissues and across a wide range of disease stages, ATPsy6 shows a relative steady state of expression compared with other endogenous controls. ATPsy6 gene expression has been used as an endogenous control in a quantitative real-time PCR assay designed to evaluate the expression of potential cancer diagnostic leads across a diverse tissue panel.

CONCLUSION

Mitochondrial ATPsy6 serves as a good endogenous control to measure target gene expression independent of the tissue- or disease-specific variation inherent with many housekeeping genes.

NBC3 expression in rabbit collecting duct: colocalization with vacuolar H+-ATPase

We have recently cloned and characterized a unique sodium bicarbonate cotransporter, NBC3, which unlike other members of the NBC family, is ethylisopropylamiloride (EIPA) inhibitable, DIDS insensitive, and electroneutral (A. Pushkin, N. Abuladze, I. Lee, D. Newman, J. Hwang, and I. Kurtz. J. Biol. Chem. 274: 16569-16575, 1999). In the present study, a specific polyclonal antipeptide COOH-terminal antibody, NBC3-C1, was generated and used to determine the pattern of NBC3 protein expression in rabbit kidney. A major band of approximately 200 kDa was detected on immunoblots of rabbit kidney. Immunocytochemistry of rabbit kidney frozen sections revealed specific staining of the apical membrane of intercalated cells in both the cortical and outer medullary collecting ducts. The pattern of NBC3 protein expression in the collecting duct was nearly identical to the same sections stained with an antibody against the vacuolar H+-ATPase 31-kDa subunit. In addition, the NBC3-C1 antibody coimmunoprecipitated the vacuolar H+-ATPase 31-kDa subunit. Functional studies in outer medullary collecting ducts (inner stripe) showed that type A intercalated cells have an apical Na+-dependent base transporter that is EIPA inhibitable and DIDS insensitive. The data suggest that NBC3 participates in H+/base transport in the collecting duct. The close association of NBC3 and the vacuolar H+-ATPase in type A intercalated cells suggests a potential structural/functional interaction between the two transporters.

Cellular and subcellular immunolocalization of ClC-5 channel in mouse kidney: colocalization with H+-ATPase

To determine the immunolocalization of ClC-5 in the mouse kidney, we developed a ClC-5-specific rat monoclonal antibody. Immunoblotting demonstrated an 85-kDa band of ClC-5 in the kidney and ClC-5 transfected cells. Immunocytochemistry revealed significant labeling of ClC-5 in brush-border membrane and subapical intracellular vesicles of the proximal tubule. In addition, apical and cytoplasmic staining was observed in the type A intercalated cells in the cortical collecting duct. In contrast, the staining was minimal in the outer and inner medullary collecting ducts and the thick ascending limb. Western blotting of vesicles immunoisolated by the ClC-5 antibody showed the presence of H+-ATPase, strongly indicating that these two proteins were present in the same membranes. Double labeling with antibodies against ClC-5 and H+-ATPase and analysis by confocal images showed that ClC-5 and H+-ATPase colocalized in these ClC-5-positive cells. These findings suggest that ClC-5 might be involved in the endocytosis and/or the H+ secretion in the proximal tubule cells and the cortical collecting duct type A intercalated cells in mouse kidney.

Antibody to H(+) V-ATPase subunit E colocalizes with portasomes in alkaline larval midgut of a freshwater mosquito (Aedes aegypti)

The pH profile, gross structure, ultrastructure and immunolabeling of the mosquito (Aedes aegypti) larval midgut are described as a first step in analyzing the role of plasma membrane H(+)V-ATPase in the alkalization of the gut, nutrient uptake and ionic regulation. Binding of an antibody to H(+)V-ATPase subunit E colocalizes with ‘portasomes’ (approximately 10 nm in diameter), which are thought to correspond to the V(1) part of the H(+) V-ATPase. In gastric caeca (pH 8), both antibody-binding sites and portasomes are located apically; in the anterior midgut (pH 10–11), they are located basally; and in the posterior midgut (pH approximately equal to 8) they are again located apically. The hypothesis that the energization of alkalization is mediated by an H(+) V-ATPase is supported by the inability of larvae to maintain the high pH after 72 h in 10 (micro)M bafilomycin B1. Confirming earlier reports, the two principal epithelial cell types are designated as ‘columnar’ and ‘cuboidal’ cells. The apical plasma membranes (microvilli) of epithelial cells in the gastric caeca and basal infoldings of anterior midgut are invaded by mitochondria that lie within approximately 20 nm of the portasome-studded plasma membranes. The colocalization of V-ATPase-immunolabeling sites and portasomes to specific plasma membranes within so-called ‘mitochondria-rich’ cells of gastric caeca and anterior midgut suggests that midgut alkalization in mosquitoes is achieved by molecular mechanisms similar to those that have been described in caterpillars, even though the gross structure of the midgut and the localization of the V-ATPase are dissimilar in the two species. In caterpillars, the high alkalinity is thought to break down dietary tannins, which block nutrient absorption; it may play a similar role in plant-detritus-feeding mosquito larvae. The colocalization of immunolabeling sites and portasomes, together with the presence of long, ‘absorptive-type’ microvilli in the posterior midgut, suggest that the V-ATPase energizes nutrient uptake there.

Localization of H(+)-ATPases in soybean root nodules

The localization of H(+)-ATPases in soybean (Glycine max L. cv. Stevens) nodules was investigated using antibodies against both P-type and V-type enzymes. Immunoblots of peribacteroid membrane (PBM) proteins using antibodies against tobacco and Arabidopsis H(+)-ATPases detected a single immunoreactive band at approximately 100 kDa. These antibodies recognized a protein of similar relative molecular mass in the crude microsomal fraction from soybean nodules and uninoculated roots. The amount of this protein was greater in PBM from mature nodules than in younger nodules. Immunolocalization of P-type ATPases using silver enhancement of colloidal-gold labelling at the light-microscopy level showed signal distributed around the periphery of non-infected cells in both the nodule cortex and nodule parenchyma. In the central nitrogen-fixing zone of the nodule, staining was present in both the infected and uninfected cells. Examination of nodule sections using confocal microscopy and fluorescence staining showed an immunofluorescent signal clearly visible around the periphery of individual symbiosomes which appeared as vesicles distributed throughout the infected cells of the central zone. Electron-microscopic examination of immunogold-labelled sections shows that P-type ATPase antigens were present on the PBM of both newly formed, single-bacteroid symbiosomes just released from infection threads, and on the PBM of mature symbiosomes containing two to four bacteroids. Immunogold labelling using antibody against the B-subunit of V-type ATPase from oat failed to detect this protein on symbiosome membranes. Only a very faint signal with this antibody was detected on Western blots of purified PBM. During nodule development, fusion of small symbiosomes to form larger ones containing multiple bacteroids was observed. Fusion was preceded by the formation of cone-like extensions of the PBM, allowing the membrane to make contact with the adjoining membrane of another symbiosome. We conclude that the major H(+)-ATPase on the PBM of soybean is a P-type enzyme with homology to other such enzymes in plants. In vivo, this enzyme is likely to play a critical role in the regulation of nutrient exchange between legume and bacteroids.

Pulsed high electric field causes 'all or nothing' membrane damage in Listeria monocytogenes and Salmonella typhimurium, but membrane H+-ATPase is not a primary target

Salmonella typhimurium (CRA 1005) was more sensitive than Listeria monocytogenes (NCTC 11994) to pulsed high electric field (PHEF) treatment in distilled water (10, 15 and 20 kV/cm), 10 mM Tris-maleate buffer, pH 7.4 (15 kV/cm) and model beef broth (0.75%, w/v; 15 kV/cm). Sublethal injury could not be detected using a selective medium plating technique, indicating that bacterial inactivation by PHEF may be an 'all or nothing' event. PHEF-induced membrane permeabilisation resulted in an increase in the leakage of UV-absorbing material from the bacteria (UV-leakage) and a decreased ability of L. monocytogenes to maintain a pH gradient. A lack of correlation between the inhibition of H+-ATPase activity and PHEF treatment, cell viability or UV-leakage indicates that this enzyme is probably not a primary site of bacterial inactivation despite its role in the maintenance of internal pH.

Na,K-ATPase and V-ATPase in ovarian follicles of Drosophila melanogaster

Uncovering the cause and meaning of bioelectric phenomena in developing systems requires investigations of the distribution and activity of ion-transport mechanisms. In order to identify and localize ion pumps in ovarian follicles of Drosophila, we used immunofluorescence microscopy, immunoelectron microscopy, subcellular fractionation, immunoblots, and acridine-orange staining. We applied various antibodies directed against the Na,K-pump (Na,K-ATPase) and against vacuolar-type proton pumps (V-ATPase). During all phases of oogenesis, Na,K-ATPase were found in apical and lateral follicle-cell membranes and, during rapid follicle growth (beginning with stage 10), also in nurse-cell membranes and in the oolemma. V-ATPase were detected in various cytoplasmic vesicles and in yolk spheres and, beginning with stage 10, also in apical follicle-cell membranes and in the oolemma. Given these and earlier results, we propose that: 1) V-ATPase coupled to secondary active antiporters represent the ouabain-intensitive potassium pumps described previously; 2) both Na,K-ATPase and V-ATPase are involved in bioelectric phenomena as well as in osmoregulation and follicle growth, especially during stages 10-12; 3) organelle-associated V-ATPase play a role in vesicle acidification and in yolk processing; and 4) the channel-forming protein ductin is a component of both V-ATPase and gap junctions in ovarian follicles of Drosophila.

Postnatal development of H+ ATPase (proton-pump)-rich cells in rat epididymis

Active proton secretion and bicarbonate reabsorption by epithelial cells of the mammalian excurrent duct system maintains an acidic luminal pH that is involved in creating a suitable environment for sperm maturation and storage. Both an apical Na/H exchanger and an apical H+ ATPase have been implicated in luminal acidification. The H+ ATPase is located in apical and/or narrow cells in the caput epididymidis, and clear cells in the corpus and cauda epididymidis. As a step toward understanding the acute and chronic regulation of luminal acidification in excurrent ducts, we have followed the appearance of H+ ATPase-rich cells in rat epididymis during postnatal development, using antibodies to subunits of the H+ ATPase. In addition, we performed double staining with antibodies against carbonic anhydrase type II (CAII). H+ ATPase-rich cells were already detectable 2 weeks after birth in all regions of the epididymis, and reached maximum numbers after 3-4 weeks. CAII-rich cells followed a similar developmental pattern. In adult rats, the number of H+ ATPase/CAII-positive cells in the cauda was on average more than double the number in the caput epididymidis, although considerable intertubule variability was seen in both regions. Double immunostaining showed that CAII and H+ ATPase were colocalized in the same cells in the caput and cauda, but H+ ATPase-rich cells in the corpus contained low levels of CAII. These results demonstrate that differentiated subpopulations of proton-secreting epithelial cells appear early during epididymal development, and that the induction of H+ ATPase in these cells occurs prior to sexual maturation.

Intercalated cell subtypes in connecting tubule and cortical collecting duct of rat and mouse

At least two populations of intercalated cells, type A and type B, exist in the connecting tubule (CNT), initial collecting tubule (ICT), and cortical collecting duct (CCD). Type A intercalated cells secrete protons via an apical H+-ATPase and reabsorb bicarbonate by a band 3-like Cl-/HCO3-exchanger, AE1, located in the basolateral plasma membrane. Type B intercalated cells secrete bicarbonate by an apical Cl-/HCO3- exchanger that is distinct from AE1 and remains to be identified. They express H+-ATPase in the basolateral plasma membrane and in vesicles throughout the cytoplasm. A third type of intercalated cell with apical H+-ATPase, but no AE1, has been described in the CNT and CCD of both rat and mouse. The prevalence of the third cell type is not known. The aim of this study was to characterize and quantify intercalated cell subtypes, including the newly described third non A-non B cell, in the CNT, ICT, and CCD of the rat and mouse. A triple immunolabeling procedure was developed in which antibodies to H+-ATPase and band 3 protein were used to identify subpopulations of intercalated cells, and segment-specific antibodies were used to identify distal tubule and collecting duct segments. In both rat and mouse, intercalated cells constituted approximately 40% of the cells in the CNT, ICT, and CCD. Type A, type B, and non A-non B intercalated cells were observed in all of the three segments, with type A cells being the most prevalent in both species. In the mouse, however, non A-non B cells constituted more than half of the intercalated cells in the CNT, 39% in the ICT, and 22% in the CCD, compared with 14, 7, and 5%, respectively, in the rat. In contrast, type B intercalated cells accounted for only 8 to 16% of the intercalated cells in the three segments in the mouse compared with 26 to 39% in the rat. It is concluded that striking differences exist in the prevalence and distribution of the different types of intercalated cells in the CNT, ICT, and CCD of rat and mouse. In the rat, the non A-non B cells are fairly rare, whereas in the mouse, they constitute a major fraction of the intercalated cells, primarily at the expense of the type B intercalated cells.