Sequential processing from cell lysis to protein assay on a chip enabling the optimization of an F(1)-ATPase single molecule assay condition

We developed an integrated protein assay device, "Single Molecule MicroTAS (SMM)," which enables cell lysis, protein extraction, purification, and activity assay. The assay was achieved at the single-molecule scale for a genetically engineered protein, F(1)-ATPase, which is the smallest known rotary motor. A cell lysis condition, with a wide range of applied voltages (50-250 V) and other optimized values (pulse width: 50 micros; duty: 0.01%; electrode gap: 25 microm; total flow rate: 5 microL min(-1)) provided a high enough protein concentration for the assay. Successively, the protein was extracted and purified by specific binding in a microfluidic channel. During the assay process, the diffusion effect of lysate between a two-phase laminar flow contributes to optimizing the single-molecule assay condition, because the concentration of the original lysate from the E. coli solution is too high to assay. To achieve the most efficient assay condition, the protein diffusion effect on the assay was experimentally and numerically evaluated. The results reveal that, in our experimental conditions, concentrations of F(1) and other contaminated effluents are optimized for the F(1) rotational assay at a channel position. The adenosine triphosphate (ATP)-driven rotation speed measured in the SMM was compatible with that obtained by conventional purification and assay. Such a sequential process from cell lysis to assay proves that the SMM is an example of a sample-in-answer-out system for F(1) protein evaluation.

Vacuolar H+-ATPase expression is increased in acid-secreting intercalated cells in kidneys of rats with hypercalcaemia-induced alkalosis

AIMS

Hypercalcaemia is known to be associated with systemic metabolic alkalosis, although the underlying mechanism is uncertain. Therefore, we aimed to examine whether hypercalcaemia was associated with changes in the expression of acid-base transporters in the kidney.

METHODS

Rats were infused with human parathyroid hormone (PTH, 15 microg kg(-1) day(-1)), or vehicle for 48 h using osmotic minipumps.

RESULTS

The rats treated with PTH developed hypercalcaemia and exhibited metabolic alkalosis (arterial HCO: 31.1 +/- 0.8 vs. 28.1 +/- 0.8 mmol L(-1) in controls, P < 0.05, n = 6), whereas the urine pH of 6.85 +/- 0.1 was significantly decreased compared with the pH of 7.38 +/- 0.1 in controls (P < 0.05, n = 12). The observed alkalosis was associated with a significantly increased expression of the B1-subunit of the H(+)-ATPase in kidney inner medulla (IM, 233 +/- 45% of the control level). In contrast, electroneutral Na(+)-HCO cotransporter NBCn1 and Cl(-)/HCO anion exchanger AE2 expression was markedly reduced in the inner stripe of the outer medulla (to 26 +/- 9% and 65 +/- 6%, respectively). These findings were verified by immunohistochemistry.

CONCLUSIONS

(1) hypercalcaemia-induced metabolic alkalosis was associated with increased urinary excretion of H(+); (2) the increased H(+)-ATPase expression in IM may partly explain the enhanced urinary acidification, which is speculated to prevent stone formation because of hypercalciuria and (3) the decreased expression of outer medullary AE2 suggests a compensatory reduction of the transepithelial bicarbonate transport.

Rat brain synaptic vesicles are devoid of Mg2+-ATPase activity and contain beta-amyloid precursor protein

Rat brain synaptic vesicles (SVs) isolated by gel filtration on Sephacryl S-500 had little Mg2+(H+)-ATPase activity, though it was identified by Western blots with antibodies against the H+-ATPase A-subunit and other vesicle proteins. In contrast, tyrosine hydroxylase and dopa decarboxylase activities in the SVs were substantial, suggesting that the absence of Mg2+(H+)-ATPase activity was not due to inactivation during isolation but rather to the nature of the SVs. The vesicle component reactive to H+-ATPase antibody was also identified in the synaptosomal cytosol, so the antibody for the A-subunit seemed unnecessary to detect H+-ATPase. The SVs contained beta-amyloid precursor protein of approximately 100 kDa. Based on these observations, SVs without Mg2+(H+)-ATPase seemed to play a role(s) in the delivery of cytoplasmic and plasma membrane proteins to nerve terminals as well as in neurotransmission.

[Water- and electrolyte secretion by salivary glands. ]

INTRODUCTION

In salivary glands, fluid transport is thought to be driven osmotically in response to transepithelial salt gradients. According to the classical two-stage hypothesis of salivary secretion, an isotonic primary fluid is generated by the acinar cells and the fluid is subsequently modified by solute reabsorption and secretion as it passes along the ductal system resulted in the final, hypotonic solution.

AIM

Very little is known about the molecular and functional nature of the transporters involved in salivary secretion, especially in human salivary glands. Therefore a systematic investigation of membrane transporters expressed also in the kidney, has been undertaken in healthy human salivary glands.

METHODS

RT-PCR and immunohistochemical analysis of different membrane transport proteins was used in rat and human salivary glands.

RESULTS

Clear evidence for the expression of aquaporin water channels in human salivary glands was found. AQP1 in the myoepithelial cells, AQP3 in the basolateral, AQP5 in the apical membrane of the acini is localized. The electroneutral NBC3 Na(+)-HCO3(-)-cotransporter is present in the apical membrane of the serous acini and of the ducts, while the NBCn1 only in the basolateral membrane of the striated duct is localized. The NHE1 Na+/H+ exchanger is present in the basolateral membrane of the acini and ducts. The vacuolar H(+)-ATPase is localized apically in the ducts, except for the intercalated duct.

CONCLUSION

Aquaporin water channels are likely to be involved in water secretion. The NBC3 and NBCn1 electroneutral Na(+)-HCO3(-)-cotransporters, the NHE1 Na+/H+ exchanger and the vacuolar H(+)-ATPase may play an important role in the pH regulation of salivary acinar and duct cells.

The Fern Adiantum capillus-veneris Lacks Stomatal Responses to Blue Light

We investigated the responses of stomata to light in the fern Adiantum capillus-veneris, a typical species of Leptosporangiopsida. Stomata in the intact leaves of the sporophytes opened in response to red light, but they did not open when blue light was superimposed on the red light. The results were confirmed in the isolated Adiantum epidermis. The red light-induced stomatal response was not affected by the mutation of phy3, a chimeric protein of phytochrome and phototropin in this fern. The lack of a blue light-specific stomatal response was observed in three other fern species of Leptosporangiopsida, i.e. Pteris cretica, Asplenium scolopendrium and Nephrolepis auriculata. Fusicoccin, an activator of the plasma membrane H(+)-ATPase, induced both stomatal opening and H(+) release in the Adiantum epidermis. Adiantum phototropin genes AcPHOT1 and AcPHOT2 were expressed in the fern guard cells. The transformation of an Arabidopsis phot1 phot2 double mutant, which lost blue light-specific stomatal opening, with AcPHOT1 restored the stomatal response to blue light. Taken together, these results suggest that ferns of Leptosporangiopsida lack a blue light-specific stomatal response, although the functional phototropin and plasma membrane H(+)-ATPase are present in this species.

Functional and Bioenergetic Consequences of AT1 Antagonist Olmesartan Medoxomil in Hearts With Postinfarction LV Remodeling

The structural left ventricular (LV) remodeling and contractile dysfunction of hearts with postinfarction LV remodeling are benefited by angiotensin II type 1 receptor (AT1) blocker. However, the myocardial bioenergetic consequences of AT1 blocker in these hearts are not known. To investigate, we used a porcine model of postinfarction LV remodeling produced by ligation of the left circumflex coronary artery. After infarction, 7 pigs received olmesartan medoxomil (2 mg/kg) for comparison against 9 untreated and 10 normal pigs. Measurements of hemodynamics, myocardial perfusion, and myocardial bioenergetics were taken 7 weeks postinfarction. The treated group had an LV-to-body weight ratio significantly lower than the untreated group (2.69 +/- 0.70, 2.96 +/- 0.51, 3.66 +/- 0.60 g/kg for control, treated, and untreated groups, respectively). The untreated group had a mean aortic pressure significantly higher than the control (73 +/- 16, 86 +/- 14, and 94 +/- 20 mm Hg, respectively). The subendocardial phosphocreatine-to-ATP ratios of the treated group were significantly higher than that of the untreated group. The untreated group, but not the treated group, had significant reductions in mitochondrial F0F1-ATPase subunits compared with controls. Congestive heart failure as evidenced by significant ascites (100 to 2000 mL) developed in 4 of the 9 untreated animals, but was absent in the treated group. Animals with heart failure demonstrated reductions in both mitochondrial F0F1-ATPase expression and myocardial high-energy phosphate levels. Thus, severe LV dysfunction and accompanying abnormal myocardial bioenergetic phenotype were prevented by the AT1 antagonist olmesartan medoxomil.

Purification, crystallization, and properties of F1-ATPase complexes from the thermoalkaliphilic Bacillus sp. strain TA2.A1

Recently, we reported the cloning of the atp operon encoding for the F(1)F(0)-ATP synthase from the extremely thermoalkaliphilic bacterium Bacillus sp. strain TA2.A1. In this study, the genes encoding the F(1) moiety of the enzyme complex were cloned from the atp operon into the vector pTrc99A and expressed in Escherichia coli in two variant complexes, F(1)-wt consisting of subunits alpha(3)beta(3)gammadeltaepsilon and F(1)Deltadelta lacking the entire delta-subunit as a prerequisite for overproduction and crystallization trials. Both F(1)-wt and F(1)Deltadelta were successfully overproduced in E. coli and purified in high yield and purity. F(1)Deltadelta was crystallized by micro-batch screening yielding three-dimensional crystals that diffracted to a resolution of 3.1A using a synchrotron radiation source. After establishing cryo and dehydrating conditions, a complete set of diffraction data was collected from a single crystal. No crystals were obtained with F(1)-wt. Data processing of diffraction patterns showed that F(1)Deltadelta crystals belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell parameters of a=121.70, b=174.80, and c=223.50A, alpha, beta, gamma=90.000. The asymmetric unit contained one molecule of bacterial F(1)Deltadelta with a corresponding volume per protein weight (V(M)) of 3.25A(3) Da(-1) and a solvent content of 62.1%. Silver staining of single crystals of F(1)Deltadelta analyzed by SDS-PAGE revealed four bands alpha, beta, gamma, and epsilon with identical M(r)-values as those found in the native F(1)F(0)-ATP synthase isolated from strain TA2.A1 membranes. ATPase assays of F(1)Deltadelta crystals exhibited latent ATP hydrolytic activity that was highly stimulated by lauryldimethylamine oxide, a hallmark of the native enzyme.

Molecular basis of morphological changes in mitochondrial membrane accompanying induction of permeability transition, as revealed by immuno-electron microscopy

The mitochondrial inner membrane typically shows a condensed structure when examined by electron microscopy. However, this typical structure is known to disappear upon induction of the mitochondrial permeability transition (PT). This change in the appearance of the mitochondrial membrane structure that accompanies the induction of PT is thought to reflect changes in the permeability of inner mitochondrial membrane; however, its molecular basis has remained uncertain. In the present study, changes in membrane status were examined by immuno-electron microscopy using antibodies against the voltage-dependent anion channel (VDAC), beta-subunit of F1-ATPase (F1beta), and cytochrome c (cyt. c). In control mitochondria, antibody against VDAC was observed at the rim of the mitochondria, whereas antibodies against F1beta and cytochrome c bound these molecules inside of the mitochondria. However, in PT-induced mitochondria, all three antibodies were observed at the mitochondrial rim. These results strongly suggest that the inner mitochondrial membrane is shoved to the rim region of mitochondria upon induction of mitochondrial PT.

Localization, morphology and function of the mitochondria-rich cells in relation to transepithelial Na(+)-transport in chicken lower intestine (coprodeum)

The correlation between morphology of the mitochondria-rich cells (MR cells) in chicken lower intestine, coprodeum, and dietary sodium levels, has been investigated, using hens with differing dietary intake of NaCl and plasma aldosterone levels. Additionally, the function of the MR cells was evaluated in relation to proton secretion/exchange. Epithelium from the coprodeum was examined by optical, transmission and scanning electron microscopy, and Na(+)-transport across the coprodeal epithelium was measured electrophysiologically in Ussing-chambers. To investigate the function of MR cells, lectin-, enzyme- and immunohistochemistry methods were used. The MR cells were generally located in the epithelium on the upper parts of the sides of mucosal folds. Long microvilli, high but variable toluidine blue affinity/electrondensity and numerous mitochondria were the main features distinguishing them from the surrounding epithelial cells. Two main MR cell types were observed, differing in microvillous morphology, diameter and toluidine blue affinity/electrondensity. This probably reflected differences in maturity and activity. The MR cells expressed a positive carbonic anhydrase reaction and a proton exchange similar to the absorptive intestinal epithelial cells, but exhibited no specific demonstrable proton secretion. A close correlation between the ultrastructure of the MR-cells, dietary sodium levels, plasma aldosterone and transepithelial Na-transport was observed.

[Proteomic analysis of the salt tolerance mutant of wheat under salt stress]

Two dimensional electrophoresis was used to analyse the proteome of the salt-tolerant mutant of wheat (RH8706-49) and the salt-sensitive mutant of wheat (H8706-34) which had been treated by 1% NaCl for 72 hours. After being analysed by MALDI-TOF-MS and Mascot software, the qualitative and quantitative differences were identified between the two materials for five candidate proteins: H+-transporting two-sector ATPase, glutamine synthetase 2 precursor, putative 33 kD oxygen evolving protein of photosystem II and ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit. These five proteins are all belong to chloroplast proteins. They are likely to play a crucial role in keeping the function of the chloroplast and the whole cells when the plant was under salt-stress.

Nectar production and transportation in the nectaries of the female Cucumis sativus L. flower during anthesis

In an effort to gain a greater understanding of nectar production, we studied the dynamic mechanisms of starch accumulation and transformation and nectar transportation in the Cucumis sativus L. female flower. Starch, which is the main precursor of nectar, accumulates in the epidermis and underlying parenchyma, with the most active accumulation occurring in the parenchyma cells within 3 days prior to anthesis. Thereafter, the starch was successively hydrolyzed and the hydrolyte was transported from the amyloplasts to vacuoles, suggesting that amyloplasts and vacuoles are the centers of nectar production. In addition, we observed few plasmodesmata and the presence of invaginated plasmalemma and electron-dense material in the intercellular spaces, suggesting that the apoplast system is involved in nectar transportation in an ATPase-dependent fashion.

Determination of proton flux and conductance at pH 6.8 through single FO sectors from Escherichia coli

We have developed a mathematical model in concert with an assay that allows us to calculate proton (H+) flux and conductance through a single FO of the F1FO ATP synthase. Lipid vesicles reconstituted with just a few functional FO from Escherichia coli were loaded with 250 mM K+ and suspended in a low K+ solution. The pH of the weakly buffered external solution was recorded during sequential treatment with the potassium ionophore valinomycin, the protonophore carbonyl cyanide 3-chlorophenylhydrazone, and HCl. From these pH traces and separate determinations of vesicle size and lipid concentration we calculate the proton conductance through a single FO sector. This methodology is sensitive enough to detect small (15%) conductance changes. We find that wild-type FO has a proton flux of 3100 +/- 500 H+/s/FO at a transmembrane potential of 106 mV (25 degrees C and pH 6.8). This corresponds to a proton conductance of 4.4 fS.

Caveolae: biochemical analysis

Caveolae appear in a multitude of processes encompassing growth regulation and trafficking. We demonstrate the abundant presence of ESA/reggie-1/flotillin-2, ATP synthase beta subunit and annexin V in endothelial caveolae by immunopurification of caveolae from vascular endothelial membrane. Five proteins are abundant in a caveolin-1 protein complex, analyzed by sucrose gradient velocity sedimentation following octyl-beta-D-glucopyranoside extraction. Caveolin-1 alpha interacts with caveolin-1beta, caveolin-2, actin, the microsomal form of NADH cytochrome B5 reductase and ESA/reggie-1/flotillin-2 as shown by co-immunoprecipitation. We propose the concept that ATP biosynthesis in caveolae regulates mechanosignaling and is induced by membrane depolarization and a proton gradient. Pressure stimuli and metabolic changes may trigger gene regulation in endothelial cells, involving a nuclear conformer of caveolin-1, shown here with an epitope-specific caveolin-1 antibody, and immediate response of ion channel activity, regulated by ESA/reggie-1/flotillin-2.

Biochemical characteristics of a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS

In an attempt to more closely define a protein basis of differences in ATPase and ATP synthase activities in a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS (3,3',4',5-tetrachlorosalicylanilide), the composition of membrane associated proteins from the wild-type and mutant strains has been compared. The uncoupler-resistance in the mutant strain was not accompanied by changes in a protein size or changes in the level of subunits A, B and c (proteolipid) of the A1A0-type ATPase-synthase. On the other hand, we revealed a 670-kDa membrane-associated protein complex that is abundantly present only in the mutant strain; it is composed of at least 5 different subunits of 95, 52, 42, 29 and 22 kDa.

The molecular chaperone, Atp12p, from Homo sapiens. In vitro studies with purified wild type and mutant (E240K) proteins

Work in Saccharomyces cerevisiae has shown that Atp12p binds to unassembled alpha subunits of F(1) and in so doing prevents the alpha subunit from associating with itself in non-productive complexes during assembly of the F(1) moiety of the mitochondrial ATP synthase. We have developed a method to prepare recombinant Atp12p after expression of its human cDNA in bacterial cells. The molecular chaperone activity of HuAtp12p was studied using citrate synthase as a model substrate. Wild type HuAtp12p suppresses the aggregation of thermally inactivated citrate synthase. In contrast, the mutant protein HuAtp12p(E240K), which harbors a lysine at the position of the highly conserved Glu-240, fails to prevent citrate synthase aggregation at 43 degrees C. No significant differences were observed between the wild type and the mutant proteins as judged by sedimentation analysis, cysteine titration, tryptophan emission spectra, or limited proteolysis, which suggests that the E240K mutation alters the activity of HuAtp12p with minimal effects on the physical integrity of the protein. An additional important finding of this work is that the equilibrium chemical denaturation curve of HuAtp12p shows two components, the first of which is associated with protein aggregation. This result is consistent with a model for Atp12p structure in which there is a hydrophobic chaperone domain that is buried within the protein interior.

Modulation of the onset of postnatal development of H(+)-ATPase-rich cells by steroid hormones in rat epididymis

Vacuolar type H(+)-ATPase is involved in lumenal acidification of the epididymis. This protein is highly expressed in narrow and clear cells where it is located in the apical pole, and it contributes to proton secretion into the lumen. We have previously shown that in rats, epididymal cells rich in H(+)ATPase appear during postnatal development and reach maximal numbers at 3-4 wk of age. The factors that regulate the appearance of these cells have not been investigated, but androgens, estrogens, or both may be involved. This study examined whether neonatal administration of estrogens (diethylstilbestrol [DES] or ethinyl estradiol) or an antiandrogen (flutamide), or the suppression of androgen production via administration of a GnRH antagonist (GnRHa), was able to alter the appearance of cells rich in H(+)-ATPase in the rat epididymis when assessed at age 25 days. Surprisingly, all of these treatments were able to significantly reduce the number of H(+)-ATPase positive cells; this was determined by immunofluorescence and confirmed by Western blotting. In contrast, neonatal coadministration of DES and testosterone maintained the expression of H(+)-ATPase in the epididymis at Day 25 despite the high level of concomitant estrogen exposure. These findings indicate that androgens, acting via the androgen receptor, are essential for the normal development of epididymal cells rich in H(+)-ATPase, and that treatments that interfere directly or indirectly with androgen production (GnRHa, DES) or action (flutamide, DES) will result in reduced expression of H(+)-ATPase. Our findings do not exclude the possibility that estrogens can directly suppress the postnatal development of cells in the epididymis that are rich in H(+)-ATPase, but if this is the case, this suppression can be prevented by testosterone administration.

Regulation of osteoclast differentiation and function by receptor activator of NFkB ligand and osteoprotegerin

The differentiation and functions of osteoclasts (OCs) are regulated by osteoblast-derived factors. Receptor activator of NFkB ligand (RANKL) is one of the key regulatory molecules in OC formation. Osteoprotegerin (OPG) is a novel secreted member of the TNF receptor superfamily that negatively regulates osteoclastogenesis and binds to RANKL. We examined the biological actions of macrophage-colony-stimulating factor (M-CSF), RANKL, and OPG on the differentiation of OCs isolated from cocultures of mouse osteoblastic cells and bone marrow cells. Preosteoclasts (pOCs) and OCs were characterized by their ultrastructure and the expression of OC markers such as tartrate-resistant acid phosphatase (TRAP) and vacuolar-type H(+)-ATPase. pOCs formed without any additives expressed TRAP, but showed little resorptive activity on cocultured dentine slices. TRAP-positive pOCs treated with M-CSF began to fuse with each other, but lacked a ruffled border (RB) and showed almost no resorptive activity. pOCs treated with RANKL became TRAP-positive multinucleated cells, which expressed intense vacuolar-type H(+)-ATPase along the RB membranes and exhibited prominent resorptive activity. Such effects of RANKL on pOCs were completely inhibited by the addition of OPG. OPG inhibited RB formation in mature OCs and reduced their resorptive activity, and also induced apoptosis of some OCs. These results suggest that 1) RANKL induces differentiation of functional OCs from pOCs, 2) M-CSF induces macrophage-like multinucleated cells, but not OCs, 3) OPG inhibits RB formation and resorptive activity in mature OCs, 4) OPG also induces apoptosis of OCs, and 5) RANKL and OPG are, therefore, important regulators of not only the terminal differentiation of OCs but also their resorptive function.

Secretory-defect distal renal tubular acidosis is associated with transporter defect in H(+)-ATPase and anion exchanger-1

Recent progress in molecular physiology has permitted us to understand pathophysiology of various channelopathies at a molecular level. The secretion of H(+) from alpha-intercalated cells is mediated by apical plasma membrane H(+)-ATPase and basolateral plasma membrane anion exchanger-1 (AE1). Studies have demonstrated the lack of H(+)-ATPase immunostaining in the intercalated cells in a few patients with distal renal tubular acidosis (dRTA). Mutations in H(+)-ATPase and AE1 gene have recently been reported to cause dRTA. This study extends the investigation of the role of transporter defect in dRTA by using immunohistochemical methods. Eleven patients with hyperchloremic metabolic acidosis were diagnosed functionally to have secretory-defect dRTA: urine pH >5.5 during acidemia, normokalemia or hypokalemia, and urine-to-blood pCO(2) <25 mmHg during bicarbonaturia. Renal biopsy tissue was obtained from each patient, and immunohistochemistry was carried out using antibodies to H(+)-ATPase and AE1. For comparison, renal tissues from the patients who had no evidences of distal acidification defect by functional studies were used: four with glomerulopathy or tubulointerstitial nephritis (disease controls) and three from nephrectomized kidneys for renal cell carcinoma (normal controls). The H(+)-ATPase immunoreactivity in alpha-intercalated cells was almost absent in all of the 11 patients with secretory-defect dRTA. In addition, 7 of 11 patients with secretory-defect dRTA were accompanied by negative AE1 immunoreactivity. In both disease controls and normal controls, the immunoreactivity of H(+)-ATPase and AE1 was strong in alpha-intercalated cells. In conclusion, significant defect in acid-base transporters is the major cause of secretory-defect dRTA.

A plasma membrane P-type H(+)-ATPase regulates intracellular pH in Leishmania mexicana amazonensis

A recent report (Mukherjee et al., J. Biol. Chem. 276 (2001) 5563) has proposed that the plasma membrane Mg(+)-ATPase of promastigotes of Leishmania donovani, that is involved in its intracellular pH regulation, is an electroneutral H(+)/K(+) antiporter rather than an electrogenic H(+) pump. Since this proposition has important implications for the use of the pump as a target for chemotherapy, we investigated its nature in the mammalian stage (amastigote) of L. mexicana amazonensis and compared it with that present in promastigotes. Intracellular pH and H(+) efflux were measured using the acetotoxymethyl ester and the free form of 2',7'-bis-(carboxyethyl)-5(and-6)-carboxyfluorescein, respectively. Intracellular pH in amastigotes (at an external pH of 5.5) and promastigotes (at an external pH of 7.4) was 6.36+/-0.02 and 6.83+/-0.07, respectively. Differences in the mechanisms for regulation of intracellular pH were noted between amastigote and promastigote forms. Amastigotes maintained their intracellular pH neutral over a wide range of external pHs in the absence of K(+) or Na(+). The H(+)-ATPase inhibitors N,N'-dicyclohexylcarbodi-imide, diethylstilbestrol and N-ethylmaleimide, substantially decreased their steady-state intracellular pH, inhibited proton efflux, and their recovery from acidification. The data support the presence of an H(+)-ATPase as the major regulator of intracellular pH in amastigotes. In contrast, promastigotes were unable to maintain a neutral pH under acidic conditions and although their steady-state intracellular pH and recovery from acidification were affected by H(+)-ATPase inhibitors, bicarbonate was able to overcome intracellular acidification. Bicarbonate was also able to raise the steady-state intracellular pH from 6.80+/-0.03 to 7.25+/-0.09 and induce membrane hyperpolarization. No evidence was found of the possible involvement of a K(+)/H(+)-ATPase in intracellular pH regulation in both developmental stages of L. m. amazonensis.

Regulation of intracellular pH in rat renal inner medullary thin limbs of Henle's loop

Regulation of intracellular pH (pHi) was studied in isolated rat renal inner medullary thin limbs of Henle's loop in bicarbonate/phosphate-buffered medium with high pCO2, high osmolality ( congruent with670 mosmol/kg H2O; 270 mM urea; 180 mM NaCl), organic osmolytes, and a pH of 6.8 to approximate the physiological in vivo environment. The pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF) was used to measure pHi. Resting pHi was always acid and significantly more acid in descending thin limb (DTL) cells than in ascending thin limb (ATL) cells from pure or mixed-type thin limbs. Resting pHi was slightly but significantly higher in both DTLs and ATLs in high osmolality ( approximately 670 mosmol/kg H2O) than in low osmolality ( approximately 290 mosmol/kg H2O) medium but not when sucrose replaced urea. In both DTLs and ATLs the rate of recovery of pHi following additional acidification with an NH4Cl pulse was reduced by Na+ removal from the medium and by the addition of 60 microM HOE642 (an inhibitor of the Na+/H+ exchanger, NHE1), 55 microM S1611 (inhibitor of Na+/H+ exchanger, NHE3), 1 microM bafilomycin A1 (an inhibitor of vacuolar H+ -ATPase), or 20 microM Schering 28080 (an inhibitor of H+ -K+ -ATPase) to the medium. Resting pHi was also reduced by 60 microM HOE642, 55 microM S1611, and 20 microM Schering 28080. In both DTLs and ATLs, RT-PCR revealed message for NHE1, NHE3, and vacuolar H+ -ATPase; immunocytochemistry demonstrated the expression of the protein for NHE1 (basolateral membrane), NHE3 (luminal membrane), and H+ -K+ -ATPase (luminal membrane). These data suggest that pHi in rat inner medullary thin limbs is regulated by urea and by basolateral and luminal H+ extrusion via NHE1, NHE3, vacuolar H+ -ATPase, and H+ -K+ -ATPase.

Immunolocalization of vacuolar-type H+-ATPase, cathepsin K, matrix metalloproteinase-9, and receptor activator of NFkappaB ligand in odontoclasts during physiological root resorption of human deciduous teeth

To investigate the cellular mechanisms of physiological root resorption in human deciduous teeth, the authors examined the immunocytochemical localization of vacuolar-type H+-ATPase, a lysosomal cysteine proteinase, cathepsin K, matrix metalloproteinase-9 (MMP-9), and receptor activator of NFKB ligand (RANKL) in odontoclasts. H+-ATPase, cathepsin K, and MMP-9 are the most important enzymes for decalcification of apatite crystals and degradation of type-I collagen. In addition, RANKL is one of the key regulatory molecules in osteoclast formation and functions. Odontoclasts developed extensive ruffled borders and clear zones apposed to the resorbing root dentine surfaces. On immunoelectron microscopy, the expression of vacuolar-type H+-ATPase was detected along the limiting membranes of pale vacuoles and the ruffled border membranes of odontoclasts. Cathepsin K in odontoclasts was localized within pale vacuoles, lysosomes, the extracellular canals of ruffled borders, and the underlying resorbing dentine surfaces. MMP-9 localization in odontoclasts was similar to those of cathepsin K. RANKL was detected in both mononuclear stromal cells and odontoclasts located on resorbing dentine surfaces. These results suggest that (1) odontoclasts are directly involved in decalcification of apatite crystals by active extrusion of proton ions mediated by H+-ATPase and (2) extracellular degradation of dentine type-I collagen by both cathepsin K and MMP-9, and (3) odontoclast differentiation and activity are regulated, at least in part, by RANKL, possibly produced by mononuclear stromal cells and odontoclasts themselves in the resorbing tissues. Thus, the cellular mechanisms of physiological root resorption appear to be quite similar to those of osteoclastic bone resorption.

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.