Vacuolar H
            <sup>+</sup>
            -ATPase in ocular ciliary epithelium

Wax, Martin B.; Saito, Isao; Tenkova, Tatyana; Krupin, Theodore; Becker, Bernard; Nelson, Nathan; Brown, Dennis; Gluck, Stephen L.

doi:10.1073/pnas.94.13.6752

Cited by 42 publications

(27 citation statements)

References 37 publications

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“…The ability of ACTZ to partially inhibit the depolarization-induced alkalinization could originate from CA-II inhibition which limits the rate of generation of cytoplasmic H + from CO 2 to replenish cytoplasmic protons pumped outward by the stimulated H + -ATPase. It is noteworthy that aqueous humor secretion can be reduced both by ACTZ (Maren, 1984) and bafilomycin A 1 , a specific inhibitor of vesicular H + -ATPase (Wax et al, 1997). Wolosin et al (1991) have suggested that the NPE could have two types of bicarbonate transport mechanisms, one sodium-dependent and one sodiumindependent.…”

Section: Discussionmentioning

confidence: 97%

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

1998

Journal of Membrane Biology

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Carbonic anhydrase (CA) inhibitors lower the rate of aqueous humor (AH) secretion into the eye. Different CA isozymes might play different roles in the response. Here we have studied the effects of carbonic anhydrase inhibitors on cytoplasmic pH (pHi) regulation, using a dextran-bound CA inhibitor (DBI) to selectively inhibit membrane-associated CA in a cell line derived from rabbit NPE. pHi was measured using the fluorescent dye BCECF and the pHi responses to the cell permeable CA inhibitor acetazolamide (ACTZ) and DBI were compared. ACTZ markedly inhibited the rapid pHi changes elicited by bicarbonate/CO2 removal and readdition but DBI was ineffective in this respect, consistent with the inability of DBI to enter the cell and inhibit cytoplasmic CA isozymes. Added alone, ACTZ and DBI caused a similar reduction (0.2 pH units) of baseline pHi. We considered whether CA-IV might facilitate H+ extrusion via Na-H exchange. The Na-H exchanger inhibitor amiloride (1 mM) reduced pHi 0.52 +/- 0.10 pH units. In the presence of DBI, the magnitude of pHi reduction caused by amiloride was significantly (P < 0.05) reduced to 0.26 +/- 0.09 pH units. ACTZ similarly reduced the magnitude of the pHi reduction. DBI also reduced by approximately 40% the rate of pHi recovery in cells acidified by an ammonium chloride (20 mM) prepulse; a reduction in pHi recovery rate was also caused by ACTZ and amiloride. DBI failed to alter the pHi alkalinization response caused by elevating external potassium concentration, a response insensitive to amiloride but sensitive to ACTZ. These observations are consistent with a reduction in Na-H exchanger activity in the presence of DBI or ACTZ. We suggest that the CA-IV isozyme might catalyze rapid equilibration of H+ and HCO3- with CO2 in the unstirred layer outside the plasma membrane, preventing local accumulation of H+ which competes with sodium for the same external Na-H exchanger binding site. Inhibition of CA-IV could produce pHi changes that might alter the function of other ion transporters and channels in the NPE.

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Section: Discussionmentioning

confidence: 97%

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

1998

Journal of Membrane Biology

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“…The distribution of the B1 "kidney" isoform is more restricted. It is found at high levels in intercalated cells of the kidney (11,12), in the ciliary epithelium of the eye (14), and in the ear (15), epididymis (16), and placenta (17). The difference in the expression of these isoforms suggests that the B subunit may function in V-ATPase regulation.…”

Section: V-atpasementioning

confidence: 99%

The Amino-terminal Domain of the B Subunit of Vacuolar H+-ATPase Contains a Filamentous Actin Binding Site

Holliday¹,

Lu²,

Lee³

et al. 2000

Journal of Biological Chemistry

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158

133

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Vacuolar H؉ -ATPase (V-ATPase) binds actin filaments with high affinity (K d ‫؍‬ 55 nM; Lee, B. S., Gluck, S. L., and Holliday, L. S. (1999) J. Biol. Chem. 274, 29164 -29171). We have proposed that this interaction is an important mechanism controlling transport of V-ATPase from the cytoplasm to the plasma membrane of osteoclasts. Here we show that both the B1 (kidney) and B2 (brain) isoforms of the B subunit of V-ATPase contain a microfilament binding site in their amino-terminal domain. In pelleting assays containing actin filaments and partially disrupted V-ATPase, B subunits were found in greater abundance in actin pellets than were other V-ATPase subunits, suggesting that the B subunit contained an F-actin binding site. In overlay assays, biotinylated actin filaments also bound to the B subunit. A fusion protein containing the amino-terminal half of B1 subunit bound actin filaments tightly, but fusion proteins containing the carboxyl-terminal half of B1 subunit, or the full-length E subunit, did not bind F-actin. Fusion proteins containing the amino-terminal 106 amino acids of the B1 isoform or the amino-terminal 112 amino acids of the B2 isoform bound filamentous actin with K d values of 130 and 190 nM, respectively, and approached saturation at 1 mol of fusion protein/mol of filamentous actin. The B1 and B2 amino-terminal fusion proteins competed with V-ATPase for binding to filamentous actin. In summary, binding sites for F-actin are present in the aminoterminal domains of both isoforms of the B subunit, and likely are responsible for the interaction between VATPase and actin filaments in vivo. V-ATPase1 is an evolutionarily ancient enzyme that performs such vital functions as acidification of lysosomes, CURL (compartments for uncoupling of receptor and ligand) compartments, and a multitude of other compartments in the vacuolar system of eukaryotic cells (2-5). In addition, certain cells express copious quantities of V-ATPase on the plasma membrane. In osteoclasts, V-ATPase is transported to a specialized domain of the apical plasma membrane, known as the ruffled membrane, that forms at the site of osteoclast attachment upon activation to resorb bone (6, 7). V-ATPases in the ruffled membrane transport protons into the resorption compartment to create the acidic pH required for bone resorption. V-ATPases are also abundant on the plasma membrane of the kidney intercalated cell, which is responsible for hydrogen ion and bicarbonate transport in the cortical and outer medullary collecting duct (8). In the H ϩ -secreting intercalated cells, V-ATPase is stored in a specialized intracellular tubulovesicular compartment, but is recruited rapidly to the apical plasma membrane in response to systemic administration of nonvolatile acid (8, 9).The V-ATPase is composed of at least 13 subunits divided into two major domains, V 1 and V 0 (2, 3). V 1 , which is composed of proteins peripheral to the membrane, contains the A, B, C, D, E, F, G, and H subunits. The A and B subunits, which share homology with the ␣ and ␤ su...

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“…The B1 isoform is part of the peripheral V 1 domain, and its yeast homolog is important for ATP binding before ATP hydrolysis by the A subunit (384). As mentioned above, two isoforms of the B subunit exist: the B2 isoform (ATP6V1B2) is ubiquitously expressed (49, 524), whereas in the kidney the B1 subunit is amplified in intercalated cells of the late distal tubule, connecting segment and cortical and medullary collecting duct (386), in narrow and clear cells of the epididymis (68, 80, 169), in the ciliary body of the eye (245,558), and in the inner ear (interdental cell layer of the spiral limbus and some epithelial cells of the endolymphatic sac) (268). The a4 subunit (ATP6V0A4) is one of four isoforms of the a subunit which forms part of the membrane-bound V 0 sector.…”

Section: "Kidney-specific" Subunits Of the Vacuolar H ؉ -Atpasementioning

confidence: 99%

Renal Vacuolar H⁺-ATPase

Wagner¹,

Finberg²,

Breton³

et al. 2004

Physiological Reviews

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413

476

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Vacuolar H+-ATPases are ubiquitous multisubunit complexes mediating the ATP-dependent transport of protons. In addition to their role in acidifying the lumen of various intracellular organelles, vacuolar H+-ATPases fulfill special tasks in the kidney. Vacuolar H+-ATPases are expressed in the plasma membrane in the kidney almost along the entire length of the nephron with apical and/or basolateral localization patterns. In the proximal tubule, a high number of vacuolar H+-ATPases are also found in endosomes, which are acidified by the pump. In addition, vacuolar H+-ATPases contribute to proximal tubular bicarbonate reabsorption. The importance in final urinary acidification along the collecting system is highlighted by monogenic defects in two subunits (ATP6V0A4, ATP6V1B1) of the vacuolar H+-ATPase in patients with distal renal tubular acidosis. The activity of vacuolar H+-ATPases is tightly regulated by a variety of factors such as the acid-base or electrolyte status. This regulation is at least in part mediated by various hormones and protein-protein interactions between regulatory proteins and multiple subunits of the pump.

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Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Cited by 42 publications

References 37 publications

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

The Amino-terminal Domain of the B Subunit of Vacuolar H+-ATPase Contains a Filamentous Actin Binding Site

Renal Vacuolar H⁺-ATPase

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Vacuolar H + -ATPase in ocular ciliary epithelium

Cited by 42 publications

References 37 publications

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

Cytoplasmic pH Responses to Carbonic Anhydrase Inhibitors in Cultured Rabbit Nonpigmented Ciliary Epithelium

The Amino-terminal Domain of the B Subunit of Vacuolar H+-ATPase Contains a Filamentous Actin Binding Site

Renal Vacuolar H+-ATPase

Contact Info

Product

Resources

About

Vacuolar H ⁺ -ATPase in ocular ciliary epithelium

Renal Vacuolar H⁺-ATPase