Regulation Of Acid-base Balance Research Articles

Is Sodium Bicarbonate Therapy Still Up To Date?

Sodium bicarbonate (SB), which has a vital role in the regulation of acid-base balance of all tissues and organs, is one of the most important buffering systems of the body. SB plays an important role in the treatment of poisoning caused by numerous agents including mainly salicylate and tricyclic antidepressants. In metabolic acidosis (MA) occurred in patient with systemic and metabolic diseases, first, the primary disease should be treated and in the case of low bicarbonate levels such as diarrhea and renal tubular acidosis, missing SB should be recovered. As the kidney has an important role in acid-base balance, SB is widely used in the treatment of acute and chronic renal failure. Although there is no conclusive evidence to prevent contrast nephropathy, SB comes to the fore compared to other agents. SB is used due to MA and its effects occurring in acute renal failure. In addition, SB treatment applied to reduce the increased acid levels in chronic kidney failure may reduce mortality. While SB can be used as individualized in lactic acidosis and cardiac arrest cases, it can be used safely as a performance enhancer for athletes. SB is used widely in gastrointestinal tract diseases due to its antacid effects and its routine use is not recommended in diabetic ketoacidosis. These data demonstrate that SB is still popular and it will retain its popularity in the near future.

Elucidating the Physiological Role of Gprc5c, a Novel Orphan GPCR in the Kidney

Kidneys play a key role in maintaining systemic homeostasis by precisely regulating a wide variety of physiological substances in both the plasma and forming urine. To aid in this process, sensory G-protein coupled receptors (GPCRs) act as specialized chemosensors to detect metabolites that often are effective 'signals' of abnormalities in essential physiological processes and metabolic pathways. Using a real-time PCR screen, we previously identified several novel GPCRs that are expressed at high levels in murine whole kidney, but have not been previously examined in the kidney. In this study, we aim to uncover the functional role of Gprc5c, which we found to be highly expressed in the kidney (at a comparable level to the well-studied and highly expressed Angiotensin receptor, AT1a; ΔCtAT1a: 6.25±0.24; ΔCtGprc5c: 7.0±0.16). Using immunohistochemistry, we found that Gprc5c is localized apically in the renal proximal tubules of wild-type (WT) mice; this stain was absent in Gprc5c knockout (KO) mice. Because Gprc5c is an orphan receptor with no known ligand, we utilized an in vitro approach to screen potential ligands using a ligand-induced GPCR internalization assay in transiently transfected HEK293T cells. We found that pH triggered Gprc5c activation and that the internalization is maximal in the alkaline range (pH>7.4). This pH range specifically induced internalization of Gprc5c, but not other transiently transfected GPCRs which served as controls. In addition, preliminary studies indicate that the plasma pH of Gprc5c knockout mice trends acidic compared to wild-type littermates (KO: 7.17±0.09, n=5; WT: 7.45±0.08, n=3, p=0.07). Together, these results indicate that Gprc5c may act in the renal proximal tubule to aid in the regulation of acid-base balance.

Acid-treatment-assisted synthesis of Pt–Sn/graphene catalysts and their enhanced ethanol electro-catalytic activity

Pt–Sn/graphene is a promising catalyst for use in direct ethanol fuel cells (DEFCs). However, under previous preparation conditions, its metal loading was found to be far lower than the nominal loading. In this study, to address this issue, improved Pt–Sn/graphene catalysts have been synthesized by an acid-treatment-assisted route. Compared with the original catalyst, we found that the Pt–Sn loading on graphene was increased due to the regulation of acid-base balance in the reaction solution, and the fragmentation of graphene sheets was also increased due to structural damage by the acid treatment. The changes in composition and microstructure resulted in an increased electrochemically active surface area (ECSA) of the Pt–Sn/graphene catalyst. The acid-treatment method can thus enhance the catalytic performance of Pt–Sn/graphene catalysts, as well as facilitate recycling of Pt and Sn lost in the preparation.

Role of IP3 receptor signaling in cell functions and diseases.

IP3 receptor (IP3R) was found to release Ca(2+) from non-mitochondrial store but the exact localization and the mode of action of IP3 remained a mystery. IP3R was identified to be P400 protein, a protein, which was missing in the cerebellum of ataxic mutant mice lacking Ca(2+) spikes in Pukinje cells. IP3R was an IP3 binding protein and was a Ca(2+) channel localized on the endoplasmic reticulum. Full-length cDNA of IP3R type 1 was initially cloned and later two other isoforms of IP3R (IP3R type 2 and type 3) were cloned in vertebrates. Interestingly, the phosphorylation sites, splicing sites, associated molecules, IP3 binding affinity and 5' promoter sequences of each isoform were different. Thus each isoform of IP3 receptor plays a role as a signaling hub offering a unique platform for matching various functional molecules that determines different trajectories of cell signaling. Because of this distinct role of each isoform of IP3R, the dysregulation of IP3 receptor causes various kinds of diseases in human and rodents such as ataxia, vulnerability to neuronal degeneration, heart disease, exocrine secretion deficit, taste perception deficit. Moreover, IP3 was found not only to release Ca(2+), but also to release IRBIT (IP3receptor binding protein released with inositol trisphosphate) essential for the regulation of acid-base balance, RNA synthesis and ribonucleotide reductase.

Hypothesis: The regulation of the partial pressure of oxygen by the serotonergic nervous system in hypoxia

The regulation of the partial pressure of oxygen by the serotonergic nervous system in hypoxia is a hypothesis, which proposes an inherent operative system in homo sapiens that allows central nervous system and endocrine-mediated vascular system adaption to variables in partial pressure of oxygen, pH and body composition, while maintaining sufficient oxygen saturation for the immune system and ensuring protection of major organs in hypoxic and suboptimal conditions.While acknowledging the importance of the Henderson–Hasselbalch equation in the regulation of acid base balance, the hypothesis seeks to define the specific neuroendocrine/vascular mechanisms at work in regulating acid base balance in hypoxia and infection. The SIA (serotonin-immune-adrenergic) system is proposed as a working model, which allows central nervous system and endocrine-mediated macro- and micro vascular ‘fine tuning’. The neurotransmitter serotonin serves as a ‘hypoxic sensor’ in concert with other operators to orchestrate homeostatic balance in normal and pathological states. The SIA system finely regulates oxygen, fuel and metabolic buffering systems at local sites to ensure optimum conditions for the immune response. The SIA system is fragile and its operation may be affected by infection, stress, diet, environmental toxins and lack of exercise.The hypothesis provides new insight in the area of neuro-gastroenterology, and emphasizes the importance of diet and nutrition as a complement in the treatment of infection, as well as the normalization of intestinal flora following antibiotic therapy.

Effect of storage on nutrient composition and mycoflora of sundried soyabean (Glycine max.)

Sundried Glycine max were stored for 20 weeks. During storage, monthly analyses were carried out to determine the effect of storage on the nutrient composition, minerals and mycoflora present in the sample. The mycoflora isolated from sundriedGlycine max during storage were Aspergillus niger, Aspergillus candidus, Aspergillus glaucus, Aspergillus versicolor, Aspergillus flavus and Rhizopus sp. The results of the proximate of stored sun dried G. max showed that moisture content increased from 6.80 to 8.34%, ash content from 5.07 to 6.45% and crude protein from 40.94 to 42.33% as the storage time increases while the fat decrease from 19.15 to 18.37%, fibre from 5.72 to 5.35% and carbohydrates from 22.33 to 19.18% with the storage time. The results of mineral analysis indicated that all the mineral elements; sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn) and phosphorus (P) were found to decrease as the storage time increased while potassium (K) and zinc (Zn) increased as the storage time increased but copper (Cu) and cadmium (Cd) were detected in the first two months of storage in the samples. Some of these isolated fungi play important role in the soil, Aspergillus spp. are common mould found in soil and the second most commonly recovered fungus in opportunistic mycoses whileRhizopus sp. is responsible for the damage of blood vessels, nerves and cause necrosis of the infected tissues. These mineral elements found in the plant serves an important role in the body system, such as teeth formation by calcium, formation of haemoglobin by iron (Fe) and regulation of acid base balance of the body by phosphorus (P). Finally, this work has shown that there is urgent need to develop a better drying method for local use since the drying methods encouraged contamination by air microflora and spores of fungi present in the air. Key words: Mycoflora, crude protein, chemical composition, soya bean, storage

Immunohistological classification of ionocytes in the external gills of larval Japanese black salamander, Hynobius nigrescens Stejneger

In this cytological and immunohistological study, we clarified the localization of the membrane transporters Na(+) , K(+) -ATPase (NKA), vacuolar-type H(+) -ATPase (VHA), and epithelial sodium channel (ENaC) and distinguished ionocyte subtypes in the gill of the Japanese salamander (Hynobius nigrescens). In larvae (IY stages 43-65), NKA immunoreactivity was observed on the basolateral plasma membrane in more than 60% cells and less than 20% cells in the primary filaments and secondary lamellae of the external gills, respectively. VHA immunoreactivity was observed on the apical membrane of some epithelial cells in the secondary lamellae of the external gills. High ENaCα immunoreactivity was widely observed on the apical cell membrane of a population of squamous cells, presumably pavement cells (PVCs), and mitochondria-rich cells (MRCs), in the primary filaments and secondary lamellae of the external gills. Using double immunofluorescence microscopy, epithelial cell types involved in ionic regulation were characterized and divided into three ionocyte types: NKA-, NKA- and ENaC-, and VHA-positive cells. VHA-immunoreactive cells as well as NKA-positive cells were observed during IY stages 43-65 of the salamander larvae. During late stages of metamorphosis, NKA, VHA, and ENaCα immunoreactivities in the external gills decreased and finally disappeared during the completion of metamorphosis (IY stage 68). PVCs and MRCs in the external gills are probably involved in acid-base balance regulation and osmoregulation in urodele amphibian larvae. The results are discussed in relation to the ionocytes previously reported in fish gills and the frog skin epithelium.

Animation-Based Lectures in Renal Physiology: Transcendence into Metacognition

Renal physiology has often been the most difficult topic for students to grasp and provides pedagogical challenge to educators. It has an inherent difficulty associated with it (intrinsic cognitive load). This inherent difficulty may not be altered by an instructor by didactic lecture or by static slides without animation (extraneous cognitive load) and it then becomes difficult for the student to understand core concepts in renal physiology like renal regulation of acid-base balance through ion exchange (eSlide). The first example is that of typical conventional diagram provided in almost all physiology text books. To learn from these diagrams learners must split their attention between various arrows to understand and grasp ion exchange. This is a typical example of Split-attention effect (extraneous cognitive load) and eludes elucidation as it has to be decoded mentally to which many learners may not be adept at and also our working memory capacity is limited. The later slides depicting “Integrated example” enhances learning because embellished with animations and displayed sequentially, it guides the learner’s attention through the worked example. The linguistic invention-animation-based lectures (ABL) as a protologism was first used by us in 2009. Majority of the students agreed that ABL helped to sustain interest, visualize concepts better, remembering facts, applying knowledge and understanding better different aspects of physiology teaching (including renal physiology)

The kidney and acid-base regulation

Since the topic of the role of the kidneys in the regulation of acid-base balance was last reviewed from a teaching perspective (Koeppen BM. Renal regulation of acid-base balance. Adv Physiol Educ 20: 132-141, 1998), our understanding of the specific membrane transporters involved in H(+), HCO(3)(-), and NH(4)(+) transport, and especially how these transporters are regulated in response to systemic acid-base disorders, has advanced considerably. In this review, these new aspects of renal function are presented, as are the broader and more general concepts related to the role of the kidneys in maintaining the acid-base balance. It is intended that this review will assist those who teach this aspect of human physiology to first-year health profession students.

Effect of a supplement rich in alkaline minerals on acid-base balance in humans

BackgroundWestern diets are considered acidogenic due to the high dietary acid load and a low intake of base-forming dietary minerals such as potassium, magnesium or calcium. In the present study we investigated the effect of a multimineral supplement (MMS) rich in alkaline minerals on acute and chronic regulation of acid-base balance with the pH of blood, urine and saliva as potential surrogate markers.MethodsParameters were measured (i) without MMS intake, (ii) in the three consecutive hours following ingestion (blood and urinary pH) and (iii) during one week with or without MMS intake (self-monitored using pH measurement strips).Results25 (15 female; 10 male) subjects (age 44 ± 14 y; BMI 23.9 ± 1.9 kg/m2) were enrolled in the investigation. Following acute administration of the MMS in the morning, blood ph (1 and 2 h after ingestion) rose from 7.40 to 7.41; p < 0.05, and also urinary pH 3 h after ingestion (5.94 to 6.57; p < 0.05) increased significantly.Following longer-term supplementation, both the increase in urinary pH in the morning and in the evening occurred within 1 day. Compared to pH values without the MMS, average pH in urine was 11% higher in the morning and 5% higher in the evening. Analyses of food records showed that the increase in urinary pH was not related to dietary change.ConclusionOur results suggest that the ingestion of a multimineral supplement is associated with both a significant increase in blood and urinary pH. The health related consequences of this supplementation remain to be determined.

Effects of Broiler Rearing Environment on Transmission of F-Strain Mycoplasma gallisepticum from Commercial Layer Hens to Broiler Chickens: Role of Acid-Base Balance

Two trials were conducted concurrently to determine and compare, blood pH, blood gases, hematocrit and hemoglobin in F-strain Mycoplasma gallisepticum (FMG) inoculated layers and FMG contactinfected broilers. At the termination of the study, FMG-inoculated layers had the highest partial pressure of O and the lowest partial pressure of CO as compared with the other treatment groups. Blood pH values 2 2 were unaffected by FMG inoculation. Hematocrit and blood concentrations of hemoglobin were slightly higher and HCO levels were lowest in FMG contact-infected broilers in comparison to the other treatments groups. 3 Mycoplasma gallisepticum inoculated layers also resulted in a significant increase in blood concentrations of K , a decrease in Na , but no significant effects on blood concentrations of Ca and Cl . There were no + + 2+ differences in plasma glucose, cholesterone, triglyceride and anion gap, but osmolality was significantly reduced in FMG contact-infected broilers. Results indicate that inoculation of layers with FMG vaccine results in changes in plasma acid-base status along with changes in other blood metabolic variables. However, the FMG inoculation did not prevent homeostatic regulation of acid-base balance, as indicated by constant blood pH. The significant increase in pO in FMG inoculated layers is generally associated with an oxygen2 dependent improvement in tissue oxygenation. Elevated arterial partial pressure of oxygen is beneficial to maximize oxygen transport capacity along with high concentrations of hemoglobin and hematocrit to carry oxygen throughout the body. It was concluded that in addition to protecting birds from MG infection, an FMG vaccine may improve the layer chicken’s ability to withstand the harmful effects of stressors on their performance and well-being.

Mechanisms of renal ammonia production and protein turnover

Renal synthesis and excretion of ammonia are critical for efficient removal of acids from the body. Besides the rate of ammonia production, the intrarenal distribution of produced ammonia is a crucial step in the renal regulation of acid-base balance. Various acid-base disorders are associated not only with changes in ammonia production but also with its distribution between the urine and the renal veins. The final effect of ammonia production on acid-base balance largely depends on the events that determine the distribution of ammonia produced between urine and blood. Several factors, among which urine pH, urine flow, total ammonia production "per se" and renal blood flow may affect the percent of ammonia excreted into urines in humans with different acid-base disturbances. Among these factors, urine pH is the most important. An additional effect of stimulated ammoniagenesis is kidney hypertrophy. In tubule epithelial cells, the associated increase in ammonia production, rather than the acidosis per se, is responsible for favoring tubular hypertrophy. This effect is related to the inhibition of protein degradation, owing to changes in lysosomal pH and cathepsin activity, without effects on cell cycle. Both changes of PI-3 kinase pathway and the suppression of chaperone-mediated autophagy are candidate mechanism for ammonia-mediated inhibition of protein degradation in tubule cells. Available data in humans indicate that the response of kidney to metabolic acidosis includes both changes in amino acid uptake and suppression of protein degradation. The latter effect is associated with the increase in ammonia excretion and partition into the urine.

Increased Acid Load and Deletion of AE1 Increase Slc26a7 Expression

Background/Aims: Slc26a7 is a member of a family of anion transport proteins, Solute-Linked Carrier 26 (Slc26). Slc26a7, which can mediate Cl^–/HCO3– exchange, is expressed in the acid-secreting, A-intercalated cells of the kidney collecting duct. On the basolateral side of the A-intercalated cells, Slc26a7 co-localizes with the anion exchanger 1 (AE1), a Cl^–/HCO3– exchanger that mediates bicarbonate reabsorption in the collecting duct. Methods: To test if Slc26a7 is involved in acid-base regulation, as its localization and function suggest, we examined the effect of acid loading and deletion of AE1 on Slc26a7 expression with quantitative real-time RT-PCR and Western blotting. Results: Four days of acid loading increased Slc26a7 mRNA expression in the kidney inner medulla by 57% (n = 6 acid loaded vs. n = 6 control rats; p < 0.001), whereas mRNA expression in the outer medulla and the cortex did not change. Western blotting analysis demonstrated increased Slc26a7 protein expression in both outer (140%) and inner medulla (50%) in acid-loaded animals (n = 3) compared to controls (n = 3; p < 0.05). The expression of Slc26a7 mRNA was increased by 66% in the kidneys of AE1 knockout mice (n = 5) compared to the wild types (n = 5, p < 0.001). The increase in Slc26a7 mRNA correlated with a twofold increase in protein expression (p < 0.05). Conclusion:We suggest that the increase in Slc26a7 expression caused by acid challenge and deletion of AE1 represents an adaptive response, indicating that Slc26a7 contributes to the regulation of acid-base balance by the kidney.

Effects of dietary strong acid anion challenge on regulation of acid-base balance in sheep1

The acid-base status of the extracellular fluid is directly affected by the concentrations of strong basic cations and strong acid anions that are absorbed into the bloodstream from the diet. The objective of this study was to develop and characterize a model for dietary acid challenge in sheep by decreasing the dietary cation-anion difference (DCAD) using NutriChlor (HCl-treated canola meal), an anionic feed supplement. Ten fully fleeced sheep (Rideau-Arcott, 54.3 +/- 6.7 kg of BW) were fed either a control supplement [200 g/d of canola meal, DCAD = 184 mEq/kg of DM, calculated as (Na+ + K+) - (Cl- + S2-)] or an anionic supplement (AS; 200 g/d of NutriChlor, DCAD = -206 mEq/kg of DM) offered twice daily at 0700 and 1100 in a randomized complete block design. The sheep were individually housed and limit-fed a basal diet of dehydrated alfalfa pellets (22% CP and 1.2 Mcal of NE(g)/kg, DM basis) at 1.1 kg of DM/d offered twice daily at 1000 and 1300. Two days before the beginning of the experiment, the sheep were fitted with vinyl catheters (0.86-mm i.d., 1.32-mm o.d.) in the left jugular vein to facilitate blood sampling. Blood and urine samples were obtained daily from 1100 to 1130 on d 1 through 9 and at 0700, 1000, 1300, 1600, and 1900 on d 10. Blood was analyzed for hematocrit, plasma pH, gases, strong ions, and total protein. Urine samples were analyzed for pH. The AS induced a nonrespiratory acid-base disturbance associated with lower (P < 0.05) plasma pH (7.47 vs. 7.39), lower (P < 0.05) urine pH (8.13 vs. 6.09), and lower (P < 0.05) strong ion difference (42.5 vs. 39.5). The AS reduced (P < 0.05) the concentration of plasma glucose, base excess, and bicarbonate and increased (P < 0.05) the concentration of K+ and Cl-. Lowering DCAD increased (P < 0.05) Ca2+ concentrations in plasma by 13%. In conclusion, this dietary model successfully induced a significant acid-base disturbance in sheep. Although the acidifying effects of negative DCAD in the diet may have short-term prophylactic effects of elevating the concentration of Ca2+ in plasma, negative DCAD may have detrimental effects on acid-base balance.

Characterization and Inhibition of the Recently Discovered Carbonic Anhydrase Isoforms CA XIII, XIV and XV

The carbonic anhydrase (CA) protein family consists of twelve active isozymes in humans and thirteen in most other mammals. The most recently discovered members of this family include cytosolic CA XIII and membrane-bound CAs XIV and XV. In this article we will review the characterization and inhibition profiles of these isozymes. CA XIII is expressed in the kidney as well as in the gastrointestinal and reproductive tracts, and therefore it may have a role in various physiological processes. The inhibition studies with CA XIII have shown that this isozyme can be inhibited efficiently with some sulfonamide inhibitors, while it is resistant to inhibition with chloride and bicarbonate ions. CA XIV is a membrane-bound enzyme that is expressed in numerous organs such as the brain, kidney, eye, liver and epididymis, where it has a role in the regulation of acid-base balance. The inhibitory properties of CA XIV have been studied, but no specific inhibitors have been found for this isozyme. The membrane-bound CA XV is an exceptional member of this protein family, because it is expressed in numerous species but absent in humans and chimpanzees. A detailed biochemical characterization of this isozyme is under way in our laboratories.

The kidney responds to respiratory acidosis by altering the fractional clearance of chloride as against sodium in pregnant ewes

Using Stewart’s physiochemical acid-base theory, we hypothesized that the kidney will balance the net excretion of chloride as against sodium in response to acute respiratory acidosis. The experiment was performed in pregnant ewes on days 118 and 125 of gestation. Ewes were placed in carts where the head resides within a sealed plexiglass chamber. Inspired CO2 concentration was manipulated for 1 hour to produce acute respiratory acidosis. When the arterial partial pressure of carbon dioxide (PaCO2) and pH changed from 32 ± 1 mm Hg and 7.52 ± 0.02 at the 0th hour to 74 ± 2 mm Hg and 7.22 ± 0.02 respectively at the 1st hour, the renal fractional clearance of chloride with respect to sodium increased significantly by 71 ± 28%. The clearance returned to baseline at 2nd hour when PaCO2 and pH were 37 ± 0.6 mm Hg and 7.49 ± 0.01 respectively. Thus, we conclude that the renal response to respiratory acidosis is to increase the strong ion difference by differential reabsorption of sodium and chloride. Since sodium reabsorption is strongly related to renal regulation of extracellular fluid volume, net chloride excretion relative to sodium is the primary mechanism for renal regulation of acid-base balance. Supported by NIAAA 10940 (T.A.C.) and the Pediatric Initiatives.

Na +/H + Exchangers in Renal Regulation of Acid-Base Balance

The kidney plays key roles in extracellular fluid pH homeostasis by reclaiming bicarbonate (HCO(3)(-)) filtered at the glomerulus and generating the consumed HCO(3)(-) by secreting protons (H(+)) into the urine (renal acidification). Sodium-proton exchangers (NHEs) are ubiquitous transmembrane proteins mediating the countertransport of Na(+) and H(+) across lipid bilayers. In mammals, NHEs participate in the regulation of cell pH, volume, and intracellular sodium concentration, as well as in transepithelial ion transport. Five of the 10 isoforms (NHE1-4 and NHE8) are expressed at the plasma membrane of renal epithelial cells. The best-studied isoform for acid-base homeostasis is NHE3, which mediates both HCO(3)(-) absorption and H(+) excretion in the renal tubule. This article reviews some important aspects of NHEs in the kidney, with special emphasis on the role of renal NHE3 in the maintenance of acid-base balance.

Stress and acid-base balance in chickens

Two trials were conducted to study the effects of continuous infusion of adrenocorticotropic hormone (ACTH) on acid-base balance in broiler chickens. Osmotic pumps delivered 8 IU of ACTH in saline/kg of BW/d for 7 d or the same saline volume as used in ACTH at 1 µL/h for 7 d. Blood samples were taken on d 0 (baseline values) and on d 4, 7, and 14 after onset of the infusions. The ACTH treatment increased the hematocrit, partial pressure of CO2, anion gap, corticosterone, mean corpuscular hemoglobin concentration, the blood concentrations of hemoglobin and HCO3-, and reduced the partial pressure of O2, plasma concentrations of Na+, K+, and Cl-. Blood pH values and plasma concentrations of Ca2+ were unaffected by ACTH treatment. The ACTH infusion also resulted in a significant increase in plasma glucose, cholesterone, high-density lipoprotein, and triglyceride. There were no differences in any of the blood constituents measured from control groups. Results indicate that infusion of ACTH resulted in changes in plasma acid-base status along with changes in other blood metabolic variables. However, the ACTH treatment did not prevent homeostatic regulation of acid-base balance, as indicated by constant blood pH. There was, however, an increased need for O2 to support gluconeogenic energy production; the birds responded by increased erythropoiesis. This adaptive response provided greater numbers of erythrocytes and thus a higher amount of circulating hemoglobin to deliver O2 for metabolism.

Characterization of CA XV, a new GPI-anchored form of carbonic anhydrase.

The main function of CAs (carbonic anhydrases) is to participate in the regulation of acid-base balance. Although 12 active isoenzymes of this family had already been described, analyses of genomic databases suggested that there still exists another isoenzyme, CA XV. Sequence analyses were performed to identify those species that are likely to have an active form of this enzyme. Eight species had genomic sequences encoding CA XV, in which all the amino acid residues critical for CA activity are present. However, based on the sequence data, it was apparent that CA XV has become a non-processed pseudogene in humans and chimpanzees. RT-PCR (reverse transcriptase PCR) confirmed that humans do not express CA XV. In contrast, RT-PCR and in situ hybridization performed in mice showed positive expression in the kidney, brain and testis. A prediction of the mouse CA XV structure was performed. Phylogenetic analysis showed that mouse CA XV is related to CA IV. Therefore both of these enzymes were expressed in COS-7 cells and studied in parallel experiments. The results showed that CA XV shares several properties with CA IV, i.e. it is a glycosylated glycosylphosphatidylinositol-anchored membrane protein, and it binds CA inhibitor. The catalytic activity of CA XV is low, and the correct formation of disulphide bridges is important for the activity. Both specific and non-specific chaperones increase the production of active enzyme. The results suggest that CA XV is the first member of the alpha-CA gene family that is expressed in several species, but not in humans and chimpanzees.

Atherosclerosis: The carbonic anhydrase, carbon dioxide, calcium concerted theory

Atherosclerosis is a dynamic multifaceted disease which affects the aorta and its major branches, characterized by the presence of lesions called atheromatous plaques. The plaque is a focal thickening of the intima caused by proliferation of smooth muscle cells, and the deposition of cholesterol, other lipids, hydroxyapatite and fibrous connective tissue. It is proposed that the determinant step of the process which leads to the disease atherosclerosis is the calcium precipitation which traps cholesterol in the plaque precursor matrix which contains lipoproteins, calcium carbonate, hydroxyapapatite, triglycerides, albumin, calmodulin and other proteins. The bear, a species which does not contract the disease is used as an example in support of the hypothesis. The bear's ability to regulate calcium levels and the regulation of acid base balance via regulation of carbon dioxide levels permits the control of the determinant step of plaque formation, that is calcification of the plaque.