Biomineralization of Trabecular Meshwork in Open-Angle Glaucoma.

A new form of open-angle glaucoma has been identified, in which calcification and silicification of the trabecular meshwork is a potentially significant component of outflow obstruction. It is noted that the mineralization of this area is promoted by various disturbances in the acid-base balance in the tissue. The role of melanosomal enzymes in the initiation of the formation of mineral calcium phosphate in trabecular tissue in open-angle glaucoma is considered.

Red cell membrane disorders.

Significant advances have been made in our understanding of the structural basis for altered cell function in various inherited red cell membrane disorders with reduced red cell survival and resulting hemolytic anemia. The current review summarizes these advances as they relate to defining the molecular and structural basis for disorders involving altered membrane structural organization (hereditary spherocytosis [HS] and hereditary elliptocytosis [HE]) and altered membrane transport function (hereditary overhydrated stomatocytosis and hereditary xerocytosis). Mutations in genes encoding membrane proteins that account for these distinct red cell phenotypes have been identified. These molecular insights have led to improved understanding of the structural basis for altered membrane function in these disorders. Weakening of vertical linkage between the lipid bilayer and spectrin-based membrane skeleton leads to membrane loss in HS. In contrast, weakening of lateral linkages among different skeletal proteins leads to membrane fragmentation and decreased surface area in HE. The degrees of membrane loss and resultant increases in cell sphericity determine the severity of anemia in these two disorders. Splenectomy leads to amelioration of anemia by increasing the circulatory red cell life span of spherocytic red cells that are normally sequestered by the spleen. Disordered membrane cation permeability and resultant increase or decrease in red cell volume account for altered cellular deformability of hereditary overhydrated stomatocytosis and hereditary xerocytosis, respectively. Importantly, splenectomy is not beneficial in these two membrane transport disorders and in fact contraindicated due to severe postsplenectomy thrombotic complications.

Band 3, the human red cell chloride/bicarbonate anion exchanger (AE1, SLC4A1), in a structural context.

The crystal structure of the dimeric membrane domain of human Band 3(1), the red cell chloride/bicarbonate anion exchanger 1 (AE1, SLC4A1), provides a structural context for over four decades of studies into this historic and important membrane glycoprotein. In this review, we highlight the key structural features responsible for anion binding and translocation and have integrated the following topological markers within the Band 3 structure: blood group antigens, N-glycosylation site, protease cleavage sites, inhibitor and chemical labeling sites, and the results of scanning cysteine and N-glycosylation mutagenesis. Locations of mutations linked to human disease, including those responsible for Southeast Asian ovalocytosis, hereditary stomatocytosis, hereditary spherocytosis, and distal renal tubular acidosis, provide molecular insights into their effect on Band 3 folding. Finally, molecular dynamics simulations of phosphatidylcholine self-assembled around Band 3 provide a view of this membrane protein within a lipid bilayer.

Citrate versus acetate-based dialysate in on-line haemodiafiltration. A prospective cross-over study.

BACKGROUND AND AIMS: A bicarbonate dialysate acidified with citrate (CD) has been reported to have local anticoagulant effect and improves biocompatibility. This study examines the effect of CD on dialysis efficiency, coagulation, acid-base status, electrolytes, and inflammation in patients in on-line hemodiafiltration (OL-HDF). METHODS: 35 patients in OL-HDF were enrolled in a prospective, cross-over study for a 24-week period and two phases alternating CD and acetate dialysate fluid (AD). Parameters on study were predialysis levels of bicarbonate and ionic calcium, reactive C Protein (CRP), and beta-2 microglobulin (B2MG) and postdialysis levels of activated tromboplastine time, bicarbonate, and ionized calcium. RESULTS: No significant differences in coagulation parameters, pH, and predialysis bicarbonate were found. The postdialysis bicarbonate and postdialysis calcium were lower with CD. Dialysis efficiency was greater with CD. Regarding inflammatory parameters, both CRP and B2MG were lower using CD. CONCLUSION: The use of CD is safe and effective in OL-HDF, and it improves dialysis efficacy, postdialysis alkalosis, and inflammation.

Mice deficient in the putative phospholipid flippase ATP11C exhibit altered erythrocyte shape, anemia, and reduced erythrocyte life span.

Transmembrane lipid transporters are believed to establish and maintain phospholipid asymmetry in biological membranes; however, little is known about the in vivo function of the specific transporters involved. Here, we report that developing erythrocytes from mice lacking the putative phosphatidylserine flippase ATP11C showed a lower rate of PS translocation in vitro compared with erythrocytes from wild-type littermates. Furthermore, the mutant mice had an elevated percentage of phosphatidylserine-exposing mature erythrocytes in the periphery. Although erythrocyte development in ATP11C-deficient mice was normal, the mature erythrocytes had an abnormal shape (stomatocytosis), and the life span of mature erythrocytes was shortened relative to that in control littermates, resulting in anemia in the mutant mice. Thus, our findings uncover an essential role for ATP11C in erythrocyte morphology and survival and provide a new candidate for the rare inherited blood disorder stomatocytosis with uncompensated anemia.

Aqp2-expressing cells give rise to renal intercalated cells.

The mammalian collecting duct comprises principal and intercalated cells, which maintain sodium/water and acid/base balance, respectively, but the epigenetic contributors to the differentiation of these cell types remain unknown. Here, we investigated whether the histone H3 K79 methyltransferase Dot1l, which is highly expressed in principal cells, participates in this process. Taking advantage of the distribution of aquaporin 2 (Aqp2), which localizes to principal cells of the collecting duct, we developed mice lacking Dot1l in Aqp2-expressing cells (Dot1l(AC)) and found that these mice had approximately 20% fewer principal cells and 13%-16% more intercalated cells than control mice. This deletion of Dot1l in principal cells abolished histone H3 K79 methylation in these cells, but unexpectedly, most intercalated cells also had undetectable di-methyl K79, suggesting that Aqp2(+) cells give rise to intercalated cells. These Aqp2(+) cell-derived intercalated cells were present in both developing and mature kidneys. Furthermore, compared with control mice, Dot1l(AC) mice had 40% higher urine volume and 18% lower urine osmolarity with relatively normal electrolyte and acid-base homeostasis. In conclusion, these data suggest that Dot1l deletion facilitates the differentiation of some α- and ß-intercalated cells from Aqp2-expressing progenitor cells or mature principal cells.

Effects of extracellular acidic-alkaline stresses on trigeminal ganglion neurons in the mouse embryo in vivo.

Acidic-alkaline stresses caused by ischemia and hypoglycemia induce neuronal cell death resulting from intracellular pH disturbance. The effects of acidic-alkaline disturbance on the trigeminal ganglion (TG) neurons of the embryonic mouse were investigated by caspase-3-immunohistochemistry and Nissl staining. TG neurons exhibited apoptosis in 3.08 ± 0.55% of neurons in intact embryos at day 16. Intraperitoneal injection of alkaline solution (pH 8.97; 0.005-0.1 M K2HPO4 or 0.01-0.04 M KOH) into the embryo at embryonic day 15 significantly increased the number of apoptotic neurons in the TG at embryonic day 16 with dependence on concentration (3.40-6.05 and 2.93-5.55%, respectively). On the other hand, acidic solutions (pH 4.4; 0.01-0.2 M KH2PO4 slightly, but not significantly, increased the number of apoptotic cells (3.64-5.15%, without dependence on concentration). Neutral solutions (pH 7.4; 0.01-0.2 M potassium phosphate buffer) had no effect on neuronal survival in the TG (2.89-3.48%). The results indicated that alkaline stress significantly increased apoptosis in the developing nervous system, but acidic stress did not.

Beyond NMDA and AMPA glutamate receptors: emerging mechanisms for ionic imbalance and cell death in stroke.

The glutamate receptor was one of the most intensely investigated targets for neuroprotection. However, numerous clinical trials of glutamate receptor antagonists for the treatment of stroke were unsuccessful. These failures have led to pessimism in the field. But recent advances could provide hope for the future. This minireview looks beyond the traditional mechanism of glutamate-receptor-driven excitotoxicity to identify other mechanisms of ionic imbalance. These advances include findings implicating sodium-calcium exchangers, hemichannels, volume-regulated anion channels, acid-sensing channels, transient receptor potential channels, nonselective cation channels and signaling cascades that mediate crosstalk between redundant pathways of cell death. Further in vivo validation of these pathways could ultimately lead us to new therapeutic targets for stroke, trauma and neurodegeneration.

Comparison of three different methods of evaluation of metabolic acid-base disorders.

OBJECTIVES: The Stewart approach states that pH is primarily determined by Pco2, strong ion difference (SID), and nonvolatile weak acids. This method might identify severe metabolic disturbances that go undetected by traditional analysis. Our goal was to compare diagnostic and prognostic performances of the Stewart approach with a) the traditional analysis based on bicarbonate (HCO3) and base excess (BE); and b) an approach relying on HCO3, BE, and albumin-corrected anion gap (AGcorrected). DESIGN: Prospective observational study. SETTING: A university-affiliated hospital intensive care unit (ICU). PATIENTS: Nine hundred thirty-five patients admitted to the ICU. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The Stewart approach detected an arterial metabolic alteration in 131 (14%) of patients with normal HCO3- and BE, including 120 (92%) patients with metabolic acidosis. However, 108 (90%) of these patients had an increased AGcorrected. The Stewart approach permitted the additional diagnosis of metabolic acidosis in only 12 (1%) patients with normal HCO3, BE, and AGcorrected. On the other hand, the Stewart approach failed to identify 27 (3%) patients with alterations otherwise observed with the use of HCO3-, BE, and AGcorrected (16 cases of acidosis and 11 of alkalosis). SID and BE, and strong ion gap (SIG) and AGcorrected, were tightly correlated (R2 = .86 and .97, p < .0001 for both) with narrow 95% limits of agreement (8 and 3 mmol/L, respectively). Areas under receiver operating characteristic curves to predict 30-day mortality were 0.83, 0.62, 0.61, 0.60, 0.57, 0.56, and 0.67 for Sepsis-related Organ Failure Assessment (SOFA) score, SIG, AGcorrected, SID, BE, HCO3-, and lactates, respectively (SOFA vs. the rest, p < .0001). CONCLUSIONS: In this large group of critically ill patients, diagnostic performance of the Stewart approach exceeded that of HCO3- and BE. However, when AGcorrected was included in the analysis, the Stewart approach did not offer any diagnostic or prognostic advantages.

Diagnosis of acid-base derangements and mortality prediction in the trauma intensive care unit: the physiochemical approach.

BACKGROUND: Conventional measures such as anion gap and base deficit can be inadequate for defining and managing complex acid-base derangements. Physiochemical analysis is an alternative approach based on the principles of electroneutrality and conservation of mass, and may be more accurate for defining the presence and type of acidosis and unmeasured anions. METHODS: We retrospectively analyzed 2,152 sets of laboratory data from 427 trauma patients admitted to the intensive care unit. All data sets included simultaneous measurements of an arterial blood gas with base deficit (BD), serum electrolytes, albumin, lactate, and a calculated anion gap (AG). Physiochemical analysis was used to calculate the corrected anion gap (AGcorr), the apparent strong ion difference, the effective strong ion difference, the strong ion gap (SIG), and the base deficit corrected for unmeasured anions (BDua). Statistical analysis comparing AG and BD to the physiochemical measures was performed on all data and the subset of admission laboratory data only (n = 427). RESULTS: Unmeasured anions as defined by an elevated SIG were present in 92% of patients (mean SIG, 5.9 +/- 3.3), whereas hyperlactatemia and hyperchloremia were present in only 18% and 21%, respectively. The physiochemical approach yielded a different clinical interpretation of the acid-base status than the conventional approach in 597 (28%) of the data sets. Lactate level was more strongly correlated with the physiochemical measures of SIG (r = 0.48) and AGcorr (r = 0.47) than with the conventional measures of AG (r = 0.24) and BD (r = 0.36, p < 0.01 for all). Both admission BD and BDua were significantly elevated in nonsurvivors, and logistic regression analysis for prediction of mortality revealed an area under the curve of 0.70 for BDua (p < 0.01) versus 0.65 for BD (p < 0.01). AGcorr and SIG did not differentiate survivors from nonsurvivors in the group as a whole. However, analysis of patients with a normal admission lactate level (n = 322) demonstrated a significant difference between survivors and nonsurvivors in SIG (7 vs. 5, p = 0.009), BDua (-4.2 vs. -2.0, p = 0.004), and AGcorr (21 vs. 19, p = 0.04), whereas the conventional measures of BD and AG showed no significant discriminatory ability. CONCLUSION: Unmeasured anions are the most common component of metabolic acidosis in trauma intensive care unit patients. The physiochemical approach can significantly alter the acid-base diagnosis compared with conventional measures. The SIG, AGcorr, and BDua may be particularly helpful in predicting acid-base derangements and mortality in patients with normal serum lactate levels.

Induction of intercalated cell changes in rat pups from acid- and alkali-loaded mothers.

We evaluated the effects of acid-base changes in pregnant and lactating dams on intercalated cell morphology and populations in newborn and 2-wk-old rats. Collecting ducts were studied with transmission electron microscopy with intercalated cells identified by the presence of 10-nm studs in the cytoplasmic face of apical membranes (A-type intercalated cells) or basolateral membranes (B-type intercalated cells). In newborn and 2-wk-old pups from dams with metabolic alkalosis, there was a significantly larger percentage of B-type intercalated cells and a smaller percentage of A-type intercalated cells. Acid loading with NH4Cl, however, did not produce an increase in the percentage of A-type intercalated cells, but reduced the percentage of B-type intercalated cells. We conclude that maternal metabolic alkalosis is associated with an increase in the percentage of B-type intercalated cells, suggesting that the initial differentiation of intercalated cells is responsive to maternal acid-base disturbances.

Mechanisms of acid damage to oesophageal epithelium: role of the paracellular pathway.

The mechanisms of acid damage to oesophageal epithelium are incompletely understood. In particular, it is unclear whether luminal acid enters and damages the oesophageal epithelium by traversing the paracellular and/or transcellular route. The present paper describes studies of the role of serosal bicarbonate ions (HCO3-) in oesophageal protection against acid damage, the results of which have direct implications regarding the route of H+ entry. The results indicate that HCO3- protects by buffering H+ within the intercellular compartment of the extracellular space, and that this protection can be mimicked almost completely by replacement of serosal HCO3- with HEPES (N-2-hydroxyethylpiperazine-N'-2-ethane sulphonic acid), a buffer that cannot permeate cells. These findings support the hypothesis that luminal acid damages oesophageal epithelium primarily by H+ diffusion through the paracellular pathway.

Leakage of HCO3- and mucosal restitution.

When the integrity of the gastric mucosa is destroyed, there is a large passive diffusion of interstitial HCO3- from the nutrient side to the luminal side of the tissue. In the absence of nutrient HCO3-, rapid repair of superficial mucosal injuries is slowed markedly down or does not take place at all. The effects of a high degree of luminal acidification, which prevents rapid repair, can be counteracted by high concentrations of nutrient HCO3-. The importance of nutrient HCO3- is emphasized by the finding that luminal acid may destroy both the fibrin network beneath which restitution occurs and the basal lamina along which viable cells must migrate to re-establish epithelial continuity. At the present time, it is not known whether the preventive effects of HCO3- against ulceration in a variety of systems are dependent upon leakage of HCO3- toward the surface, or whether nutrient HCO3- actually enters cells in order to regulate intracellular pH.

[Acid-base balance of the blood and possible renal mechanisms of its imbalance in children with oxalate-phosphate stones of the urinary tract]. / Kislotno-shchelochnoe sostoianie krovi i vozmozhnye pochechnye mekhanimy ego narusheniia u detei s oksalatno-fosfatnymi kamniami mochevyvodiashchikh putei.

A total of 191 children with oxalate-phosphate urinary concrements and 28 virtually healthy ones were studied for the main parameters of acid-base blood status with the use of Astrup's microtest. Besides, the urine circadian levels of acid and ammonium were followed up too. The proportion of the main and H+-secreting insertion cells of collecting tubes were calculated in 46 operative biopsy specimens, cells studied with electron microscopy. Advanced metabolic acidosis associated with a decrease in acid and ammonium titration was diagnosed in all patients with bilateral and in 81.6 per cent with unilateral nephrolithiasis. Regardless of acid-base blood status biopsy examination revealed a decrease in the number of insertion cells in renal collecting tubes of the patients mostly pronounced in those with bilateral concrement localization. Ultrastructure of insertion cells in children with oxalate-phosphate urolithiasis featured by a sharp decrease in mitochondria number, absence of smooth-walled vesicles, frequency of myelinoid lysosomes pointed to the failed competence of these cells to efficient H+ secretion. The data obtained evidence of the relationship between the metabolic acidosis and primary disability of the children's kidney to excrete H+.

Laxative abuse syndrome.

Laxative abuse syndrome (LAS) is a type of Münchausen syndrome characterized by surreptitious abuse of purgatives. Clinical findings are often perplexing and may mimic inflammatory bowel disease or malabsorption syndromes. Patients frequently complain of diarrhea alternating with constipation and may have nausea, vomiting and weight loss. Psychiatric disturbances are common and may include anorexia nervosa. Melanosis coli and cathartic colon, acid-base disturbances (usually metabolic alkalosis), sodium, potassium and water depletion, hyperuricemia, hyperaldosteronism and other electrolyte changes are possible complications. Diagnosis may be extremely difficult and may require special chemical analysis of urine and feces and search of the patient's possessions. Treatment is frustrating because the patient is rarely willing to admit to laxative abuse let alone cooperate in attempting to stop it. Physicians must be aware of the LAS in order to avoid harming the patient with extensive, expensive and often invasive (including laparotomy) procedures.