Extracellular Hydrogen Ion Concentration Research Articles

Acid stress reduces the function of Na+-K+-ATPase in superior mesenteric artery of Capra hircus

Context: Extracellular hydrogen ion concentration (pH o ) is an important physiological regulator of vascular tone, maintained within 7.35–7.45 and any change in it leads to complex health problem including maintenance of normal blood pressure. Aims: This study aims to examine the altered function of Na + -K + pump and inward rectifier potassium channels (K ir ) channels in extracellular acidosis in goat superior mesenteric artery (GSMA). Subjects and Methods: Isolated GSMA rings were mounted in an automatic organ bath containing 20-ml modified Krebs–Henseleit solution at pH 7.4/6.8/6.0 and KCl-induced contraction was elicited either in the absence or presence of ouabain, barium (Ba 2+ ), and combination of ouabain and Ba 2+ . Rings were dilated with potassium chloride either in the absence or presence of ouabain, Ba 2+ and combination of ouabain and Ba 2+ while maintaining at acidic pH. The responses were recorded isometrically by highly sensitive isometric force transducer connected to Powerlab and analyzed using LabChart 7.1.3 software. Statistical Analysis Used: Data were analyzed in GraphPad Prism 5 software. Results: K + vasorelaxation response in K + -free solution precontracted rings the percent maximal response (93.57 ± 2.57%, 62.60 ± 3.56%, and 53.38 ± 5.41%) was decreased with decrease pH o (7.4, 6.8 and 6.0). Ouabain, Ba 2+ , and ouabain and Ba 2+ inhibited the maximal vasorelaxation of potassium chloride (26.20 ± 3.48%, 17.39 ± 0.54%, 31.92 ± 1.10%) at pH o 7.4, (42.74 ± 2.48%, 16.12 ± 3.49%, 22.32 ± 1.63%) at pH o 6.8, and (53.87 ± 2.18%, 25.24 ± 2.90%, 39.71 ± 0.14%) at pH o 6.0, respectively. Conclusions: Attenuated vasodilation in acidosis is due to reduced function or expression of ouabain-sensitive sodium–potassium ATPase (Na + -K + -ATPase) and K ir channels. In clinical acidosis, agents augmenting the activity of Na + -K + -ATPase and K + -Channel could improve hypertensive crisis. Abbreviations used: Ba 2+ : Barium; E max : Percent maximal response; E Bmax : Percent maximal response in presence of antagonist; K ATP : Adenosine triphosphate-sensitive potassium channel; K ir : Inward rectifier potassium channels; K Ca : Calcium-activated potassium channels; Na + -K + -ATPase: Sodium–potassium ATPase; NO: Nitric oxide; pH i : Intracellular hydrogen ion concentration; pH o : Extracellular hydrogen ion concentration; VSMCs: Vascular smooth muscle cells.

Silencing of vacuolar ATPase csubunit ATP6V0C inhibits the invasion of prostate cancer cells through a LASS2/TMSG1-independent manner.

Vacuolar ATPase (V-ATPase), widespread in eukaryotic cells, is extensively expressed in many highly metastatic tumors, of which the V-ATPase csubunit ATP6V0C is particularly associated with the invasion and metastasis of cancer. ATP6V0C was directly found to interact with LASS2/TMSG1 which is a new tumor metastasis inhibitory gene identified by our laboratory in 1999. In order to study the role of ATP6V0C, we generated small interference RNA (siRNA) targeting ATP6V0C and investigated its function on the invasion of human prostate cancer cell line PC-3M-1E8 with high metastatic potential and its interplay with LASS2/TMSG1. We found that the expression of ATP6V0C was higher in prostate cancer cell lines PC-3M-1E8 and PC-3M with high metastatic potential than that from cell lines PC-3M-2B4 and PC-3 with low metastatic potential, indicating that ATP6V0C enhanced metastatic capacity in prostate cancer cells. Furthermore, silencing of ATP6V0C in PC-3M-1E8 cells inhibited V-ATPase activity (by ~5-fold), decreased extracellular hydrogen ion concentration and successively decreased activation of secreted MMP-9 (by ~3.6-fold), which coincided with the inhibition of cell migration and invasion invitro, as well as a marked decrease in the expression of LASS2/TMSG1 probably through positive feedback. Thus we concluded that silencing of the ATP6V0C gene effectively suppressed the migration and invasion of prostate carcinoma cells through the inhibition of the function of V-ATPase, not through a LASS2/TMSG1-dependent manner. Therefore ATP6V0C inhibitors are promising therapeutic targets for advanced prostate cancer.

LASS2 inhibits growth and invasion of bladder cancer by regulating ATPase activity.

Homo sapiens longevity assurance homolog 2 of yeast LAG1 (LASS2) is a novel suppressor of human cancer metastasis, and downregulation of LASS2 has been associated with a poor prognosis in patients with bladder cancer (BC). However, the molecular mechanism underlying LASS2-mediated inhibition of tumor invasion and metastasis in BC remains unclear. LASS2 has been reported to directly bind to subunit C of vacuolar H+-ATPase (V-ATPase) in various types of cancer, suggesting that LASS2 may inhibit cancer invasion and metastasis by regulating the function of V-ATPase. The present study investigated the effect of LASS2-specific small interfering (si)RNA on the invasion and metastasis of the RT4 human BC cell line, which has a low metastatic potential, and its functional interaction with V-ATPase. Silencing of LASS2 in RT4 cells was able to increase V-ATPase activity, the extracellular hydrogen ion concentration and, in turn, the activation of secreted matrix metalloproteinase (MMP)-2 and MMP-9, which occurred simultaneously with enhanced cell proliferation, cell survival and cell invasion in vitro, as well as acceleration of BC growth in vivo. In this process, it was found that siRNA-LASS2 treatment was able to suppress cell apoptosis induced by doxorubicin. These findings suggest that silencing of LASS2 may enhance the growth, invasion and metastasis of BC by regulating ATPase activity.

CERS2 suppresses tumor cell invasion and is associated with decreased V-ATPase and MMP-2/MMP-9 activities in breast cancer.

Ceramide synthase 2 (CERS2) is the gene identified from a human liver cDNA library in 2001. Our previous studies have shown higher expression of CERS2 in the breast cancer patients was associated with fewer lymph node metastases. However, the molecular mechanism of CERS2 involved is unknown. Here, we found CERS2 was heterogeneously expressed in various breast cancer cells. The mRNA and protein expression levels of CERS2 in MCF7 cells, which are poorly invasive breast cancer cells, were obviously higher than that in the highly invasive cells MDA-MB-231. Results showed overexpression of CERS2 in MDA-MB-231 cells could significantly inhibit the migration and invasion ability, whereas CERS2 knockdown in MCF7 cells could significantly increase the migration and invasion ability. Overexpression of CERS2 in MDA-MB-231 cells significantly reduced the V-ATPase activity, increased the extracellular pH and decreased the pH-dependent activity of MMP-2 and MMP-9 matrix metalloproteinases (MMPs). CERS2 knockdown in MCF7 cells significantly increased the V-ATPase activity, decreased the extracellular pH and increased the activity of MMP-2 and MMP-9. Taken together, CERS2 can significantly inhibit breast cancer cell invasion and is associated with the decrease of the V-ATPase activity and extracellular hydrogen ion concentration, and in turn the activation of secreted MMP-2/MMP-9 and degradation of extracellular matrix (ECM), which ultimately suppressed tumor's invasion. Thus, CERS2 may represent a novel target for selectively disrupting V-ATPase activity and the invasive potential of cancer cells.

LASS2/TMSG1 inhibits growth and invasion of breast cancer cell in vitro through regulation of vacuolar ATPase activity.

Homo sapiens longevity assurance homologue 2 of yeast LAG1 (LASS2)/tumor metastasis suppressor gene 1 (TMSG1) was a novel tumor metastasis-related gene identified using messenger RNA differential display from non-metastatic human prostate cancer cell variants. The mechanism of LASS2/TMSG1 inhibiting tumor invasion metastasis in breast cancer cells had not been well investigated. In the present study, a full length of 1.2kb LASS2/TMSG1 complementary DNA (cDNA) coding for a protein of 380 amino acids was cloned. PcDNA3 eukaryotic expression plasmids of LASS2/TMSG1 were constructed and transfected into human breast cancer cell line MCF-7 by lipofectin transfection method. And, the biological effects were observed comparing with control groups. As the result, LASS2/TMSG1 inhibited cell growth in vitro by increasing apoptosis and changing cell cycle distribution. Furthermore, the vacuolar ATPase (V-ATPase) activity and extracellular hydrogen ion concentration were significantly decreased and the activity of secreted matrix metalloproteinase-2 (MMP-2) was downregulated in MCF-7 cells overexpressing LASS2/TMSG1 compared with the controls. Therefore, LASS2/TMSG1 may inhibit growth and invasion of breast cancer cell in vitro through decreasing V-ATPase activity and extracellular hydrogen ion concentration and inactivating secreted MMP-2. The findings provided the evidence that the LASS2/TMSG1 gene had tumor growth and invasion suppressor function in human breast cancer cell and may provide a promising target for cancer metastasis diagnosis and therapy.

LASS2/TMSG1 gene silencing promotes the invasiveness and metastatic of human prostatic carcinoma cells through increase in vacuolar ATPase activity

To explore the effects of LASS2/TMSG1 silencing on the growth, invasion and metastasis of prostate carcinoma cells and to investigate the related molecular mechanisms. LASS2/TMSG1 expression of human prostate carcinoma cell line with low metastatic potentiality (PC-3M-2B4 cells) was knocked down using DNA vector-based small interfering RNA (shRNA), followed by evaluations of tumor cell invasion and metastasis. A stable PC-3M-2B4 cell line with expression of LASS2/TMSG1-shRNA was successfully established. MTT assay showed PC-3M-2B4 cells exhibited a strong proliferation after transfection of LASS2/TMSG1-shRNA.LASS2/TMSG1-shRNA transfected clones demonstrated an increased clonogenicity by soft agar colony formation assay and a significant increase of tumor cell invasion by matrigel invasion study.Flow cytometry showed that after LASS2/TMSG1 gene silencing, the apoptotic rate of PC-3M-2B4 cell significantly decreased (P<0.01) without significant cell cycle change (P>0.05).Eight weeks after implantation into subcutaneous tissues in BAL B/c (nu+) mice, the size and weight of sh-LASS2/TMSG1 xenografts were significantly larger than those of the control group (P<0.05).Nuclear proliferation index of the subcutaneous tumor was also higher in the LASS2/TMSG1 shRNA group than those in the control group. Lymph node metastasis was observed in 5 of 6 mice of LASS2/TMSG1 shRNA group and only 1 of 6 of the control group. V-ATPase activity, activities of secreted MMP-2 and MMP-9 and extracellular hydrogen ion concentration were significantly increased in LASS2/TMSG1-shRNA group compared with the control group (P<0.05). Silencing of LASS2/TMSG1 promotes the growth, invasion and metastasis of prostate cancer cells through up-regulation of V-ATPase activity, indicating that LASS2/TMSG1 is a tumor metastasis suppressor gene.

Silencing of LASS2/TMSG1 enhances invasion and metastasis capacity of prostate cancer cell

Homo sapiens longevity assurance homolog 2 of yeast LAG1 (LASS2), also known as tumor metastasis suppressor gene 1 (TMSG1), was firstly cloned by our laboratory in 1999. However, its antitumor molecular mechanisms are still unclear. LASS2/TMSG-1 could directly interact with the C subunit of Vacuolar H(+) ATPase (V-ATPase), which suggested that LASS2/TMSG1 might inhibit the invasion and metastasis through regulating the function of V-ATPase. In this study, we explored the effect of small hairpin RNA (shRNA) targeting LASS2/TMSG1 on the invasion and metastasis of human prostate carcinoma cell line PC-3M-2B4 with low metastatic potential and its functional interaction with V-ATPase. Silencing of LASS2/TMSG1 gene in PC-3M-2B4 cells increased V-ATPase activity, extracellular hydrogen ion concentration and in turn the activation of secreted MMP-2 and MMP-9, which coincided with enhancing cell proliferation, cell survival, and cell invasion in vitro, as well as acceleration of prostate cancer (PCA) growth and lymph node metastases in vivo. Thus we concluded that silencing of LASS2/TMSG1 enhances invasion and metastasis of PCA cell through increase of V-ATPase activity. These results establish LASS2/TMSG1 as a promising therapeutic target for advanced PCA.

Silencing of a novel tumor metastasis suppressor gene LASS2/TMSG1 promotes invasion of prostate cancer cell in vitro through increase of vacuolar ATPase activity

Homo sapiens longevity assurance homologue 2 of yeast LAG1 (LASS2), also known as tumor metastasis suppressor gene 1 (TMSG1), is a newly found tumor metastasis suppressor gene in 1999. Preliminary studies showed that it not only suppressed tumor growth but also closely related to tumor metastasis, however, its molecular mechanisms is still unclear. There have been reported that protein encoded by LASS2/TMSG-1 could directly interact with the C subunit of Vacuolar ATPase (V-ATPase), which suggested that LASS2/TMSG1 might inhibit the invasion and metastasis through regulating the function of V-ATPase. Thus, in this study, we explored the effect of small interference RNA (siRNA) targeting LASS2/TMSG1 on the invasion of human prostate carcinoma cell line PC-3M-2B4 and its molecular mechanisms associated with the V-ATPase. Real-time fluorogentic quantitative PCR (RFQ-PCR) and Western blot revealed dramatic reduction of 84.5% and 60% in the levels of LASS2/TMSG1 mRNA and protein after transfection of siRNA in PC-3M-2B4 cells. The V-ATPase activity and extracellular hydrogen ion concentration were significantly increased in 2B4 cells transfected with the LASS2/TMSG1-siRNA compared with the controls. The activity of secreted MMP-2 was up-regulated in LASS2/TMSG1-siRNA treated cells compared with the controls; and the capacity for migration and invasion in LASS2/TMSG1-siRNA treated cells was significantly higher than the controls. Thus, we concluded that silencing of LASS2/TMSG1 may promote invasion of prostate cancer cell in vitro through increase of V-ATPase activity and extracellular hydrogen ion concentration and in turn the activation of secreted MMP-2.

Effect of Hypoxemia and Hyperglycemia on pH in the Intact Cat Retina

To examine the effects of acute hypoxemia and hyperglycemia on retinal pH to understand hyperglycemia-induced changes in the normal intact cat retina. Spatial profiles of extracellular hydrogen ion (H+) concentration were obtained from the cat retina, in vivo, using pH-sensitive microelectrodes during normoxia (arterial partial pressure of oxygen [PaO2] = 114.5 +/- 7.9 mm Hg), normoglycemia (plasma glucose concentration, 117 +/- 19 mg/dL), acute hypoxemia (PaO2 = 29.5 +/- 2.2 mm Hg), and acute hyperglycemia (plasma glucose concentration, 303 +/- 67 mg/dL). An H+ diffusion model was fitted to the outer retinal data to quantify photoreceptor H+ production. The inner retinal pH was also examined. Hypoxemia induced a mean acute panretinal acidification of 0.16 pH units that originated from a 2.55-fold increase in net photoreceptor H+ production. Hyperglycemia induced an acute panretinal acidification of 0.12 pH units; however, photoreceptor H+ production levels remained unchanged. Retinal pH changes followed the course of arterial PaO2 and blood glucose changes. The increase in photoreceptor H+ production during hypoxemia confirms the importance of glycolysis in the retina. Hyperglycemia-induced pH changes resulted from either increased inner retinal H+ production or decreased H+ clearance/neutralization. Clinical Relevance The hyperglycemia-induced acidification that originates in the inner retina suggests that retinal acidosis may contribute to the development of diabetic retinal disease.

Characterization of efferent projections of chemosensitive neurons in the caudal parapyramidal area of the rat brain

The caudal parapyramidal area of the rat brain contains a population of neurons that are highly sensitive to an increase in the extracellular hydrogen ion concentration ([H +] o). Some of them fire synchronously with respiration when [H +] o is increased. These chemosensitive neurons are located in the caudal ventrolateral medulla in a medial region, closest to the pyramidal tract, and a lateral region, beneath the lateral reticular nucleus. To assess the nature of medullary connections, biotinylated dextran amine injections were performed after recordings from the neurons had been completed. The injections were located within the areas containing serotonergic neurons of the caudal parapyramidal area. The injections within the medial and lateral parts of the caudal parapyramidal region revealed bilateral terminal fields of varicosities within the nucleus of the solitary tract and the ventral respiratory column. Efferent bilateral projections to the lateral paragigantocellular, lateral reticular, and inferior olive nuclei, as well as ipsilateral projections to medial and lateral caudal parapyramidal regions were also identified. Efferent projections towards the raphe obscurus from both medial and lateral caudal parapyramidal regions were found. Medial caudal parapyramidal regions also sent efferent projections towards the raphe pallidus, B1–B3 region, and to the dorsal and ventral parts of the medullary reticular nuclei. The detection of H +-sensitive neurons in the caudal parapyramidal area and their projections towards the nucleus of the solitary tract and to the ventral respiratory column, associated with respiratory regulation, indicate that this region could be an excellent candidate for central chemoreception.

Acidic pH and capsaicin activate mechanosensitive group IV muscle receptors in the rat

Strenuous exercise of muscle as well as inflammation and ischaemia are associated with tissue acidosis. However, so far, nothing is known about the sensitivity to hydrogen ions of slowly conducting muscle afferent units. The study investigated if acid-sensing ion channels, e.g. the polymodal acid/capsaicin-sensitive vanilloid receptors, were present on unmyelinated (group IV) muscle afferent units of the gastrocnemius-soleus muscle of the rat. Intramuscular injections of acidic phosphate buffer pH 6 excited 56.0% of the group IV units. A similar proportion (54.29%) was activated by capsaicin (655 μM). Tests of the same unit with both adenosine triphosphate at neutral pH (ATP, 7.6 mM; pH 7.4) and acidic phosphate demonstrated that most acid-sensitive units were also excited by ATP at neutral pH. The data show that (1) a high proportion of group IV muscle receptors are responsive to an increased extracellular hydrogen ion concentration, and (2) a subpopulation of these units are sensitive to both acidic pH and ATP.

Disorders of mineralocorticoid synthesis.

Abnormalities of mineralocorticoid synthesis and/or metabolism profoundly affect the regulation of electrolyte and water balance and of blood pressure. Characteristic changes in extracellular potassium, sodium and hydrogen ion concentrations are usually diagnostic. Serious deficiency may be acquired, for example in Addison's disease, or inherited. In most of the inherited syndromes, the precise molecular changes in specific steroidogenic enzymes have been identified. Mineralocorticoid excess may be caused by aldosterone or 11-deoxycorticosterone by inadequate conversion of cortisol to cortisone by 11beta-hydroxysteroid dehydrogenase type 2 in target tissues (see Chapter 4), by glucocorticoid receptor deficiency or by constitutive activation of renal sodium channels. Changes in electrolyte balance and renin as well as the abnormal pattern of corticosteroid metabolism are usually diagnostic. Where these abnormalities are inherited (e.g. 11beta- or l7alpha-hydroxylase deficiencies, glucocorticoid remediable hyperaldosteronism (GRA), receptor defects, Liddle's syndrome), the molecular basis is again usually known and, in some cases, may provide the simplest diagnostic tests. Primary aldosteronism, although readily identifiable, presents problems of differential diagnosis, important because optimal treatment is different for each variant. Moreover, the mechanisms by which the variants develop are poorly understood. Finally, a significant proportion of patients with essential hypertension show characteristics of mild mineralocorticoid excess, for example low renin levels. Is this relevant to pathophysiology and, if so, is the effect induced via classic mechanisms of action or through newly discovered direct actions on the brain, heart and blood vessels? These questions are the subject of current research.

Extreme derangements of acid-base balance in exercise: advantages and limitations of the Stewart analysis.

The acid-base analysis method described by Stewart (1981) was applied to the greyhound, an animal that undergoes large changes in intra- and extracellular hydrogen ion concentrations during a race. Increases in plasma [H+] especially during the first 15 min of recovery, induced by increases in lactate concentration in the plasma, were reduced by lowering of PCO2 (hyperventilation) and removal of Cl- from the plasma. [H+] calculated by the Stewart method is similar to that measured directly with a pH electrode when the strong ion difference is within 10 meq/L of resting values (approximately 40 meq/L); thus the measured independent variables were sufficient to account for the [H+] using the Stewart analysis. When the strong ion difference became lower than 30 meq/L, increased variability between measured and calculated [H+] occurred. An error analysis demonstrated the importance of minimizing measurement error of all independent variables, including as many strong and weak electrolytes as possible in the analyses, using the most accurate dissociation constants possible, and understanding the dissociation behavior of the weak electrolytes, especially the plasma proteins, when using the Stewart analysis. The Stewart method of analyzing acid-base balance can contribute to improved training methods for obtaining maximum exercise performance.

Understanding the dynamics of cellular responsiveness to modifications of metabolic substrates in perifusion

A novel microperifusion system with capabilities for continuous, real-time, potentiometric monitoring of extracellular hydrogen ion concentration has been used to define the response of HeLa cells to abrupt changes in extracellular energy sources or introduction of an inhibitor of glycolysis. Glycolytic inhibition, induced by removal of glucose or introduction of iodoacetate, each led to a rapid, continuous decrease in acid release. The response to iodoacetate took longer than removal of glucose, perhaps due to the time required for binding and activation. Once inhibition began, however, the rate of change was greater than following glucose removal. Conversely, recovery time following iodoacetate inhibition was much slower than with glucose removal. Unlike the response to short-term glucose depletion, a second pulse of iodoacetate resulted in a faster response followed by an even longer recovery time. The response to switching between glucose and glutamine began almost without evident delay. The response patterns revealed that HeLa cells prefer glutamine to glucose, but, in the presence of both energy sources, some glucose continues to be used. In summary, these results indicate that continuous, real-time monitoring of the kinetics of hydrogen-ion release can be used to gain new insights into the dynamics of cellular response to perturbations of extracellular energy sources.

Factors affecting nerve excitability and conduction as a basis for desensitizing dentine

Nerve excitability is principally determined by the state of membrane sodium channels, which can be influenced by factors such as drugs or the ionic composition of the extracellular fluids. The excitability of isolated nerves is increased by lowered extracellular calcium and hydrogen ion concentrations, and similar effects are seen on intradental nerve excitability. This is of interest as some agents used to desensitize hypersensitive dentine are believed to act by reducing intradental nerve excitability. A variety of ions, including potassium and divalent cations, have been shown to reduce intradental nerve excitability when applied in relatively high concentrations to dentine close to the pulp. However, these conditions do not mimic the clinical situation, where agents are applied to outer dentine, up to 2 mm from the pulp. Also, when agents are applied to dentine it is difficult to quantify the precise changes in extracellular fluid composition, and there is the additional complication of possible interactions between the agents and dentine. These problems can be minimized by using isolated nerves, which allow better control over the conditions and ionic concentrations necessary to achieve nerve conduction block. Such methods can provide a convenient way to screen potential desensitizing agents before evaluation in vivo or in clinical trials.

Manipulation of intra- and extracellular pH in spontaneous canine tumours by use of hyperglycaemia.

We evaluated the use of hyperglycaemia to reduce tumour pH in dog with spontaneous tumours. Dogs were randomized to two groups: control and glucose. Intravenous administration of 20% glucose was used to induce and maintain hyperglycaemia. Extra- and intracellular tumour pH were measured using interstitial pH microelectrodes and 31P-MRS, respectively. During the administration of glucose, the mean (+/- SEM) blood glucose concentration was 419.8 (+/- 32.8) and 121.1 (+/- 8.0) mg/dl for the glucose and control groups, respectively. The mean extracellular tumour pH before and following 90 min of hyperglycaemia was 7.15 (+/- 0.08) and 7.15 (+/- 0.09). During consecutive measurements, intracellular tumour pH did not change significantly for the control group or the group subjected to hyperglycaemic manipulation. In contradistinction to previous rodent studies, our results demonstrate that hyperglycaemia alone is not sufficient to manipulate either intra- (pHi) or extracellular (pHe) hydrogen ion concentration in spontaneous canine soft tissue tumours.

Potassium and sodium transport and pH regulation.

The excitatory and metabolic events in nervous tissue lead to localized increases in extracellular potassium (K+) and intracellular hydrogen (H+) and calcium (Ca2+) ion concentrations. Even more pronounced increases are seen under pathological conditions and may interfere with the maintenance of cellular function and structure. Most presentations on the second day focused on these processes and the mechanisms for the clearance of K+, H+, and Ca2+ from intra- or extra-cellular compartments. The essential role of glial cells was a returning theme. Extracellular K+ is transported into cells by the Na-K pump and by two other processes, Na-K-Cl2 cotransport and spatial buffering, which both depend on the operation of the Na-K pump. The clearance of H+ from the cytoplasm and into the extracellular space is mediated by Na+ gradient dependent processes, Na+/H+ antiport, Cl-/HCO3- exchange, and Na(+)-HCO3- cotransport. Also the clearance of cytoplasmic Ca2+ is to a large extent mediated by a Na+ gradient dependent process, the Na+/Ca2+ antiport. There is a wide divergence between the rates of Na-K pump mediated K+ influx measured in various cultures of glial and neuronal cells. There is a considerable need for systematic comparison between the functional capacity and the concentration of Na-K pumps in cell cultures and intact nervous tissue. It has not yet been ascertained whether K+ transport as measured in cultured astrocytes is representative for K+ transport in the in situ functioning astrocyte. In astrocytes, glutamate was shown to elicit a rapid intercellular propagation of a rise in cytoplasmic Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of plasma aldosterone by physiological changes in hydrogen ion concentration.

To assess the effect of extracellular hydrogen ion concentration (PH+) on aldosterone secretion, studies in which other known modulators could be controlled were performed on 13 patients undergoing hemodialysis. High (35 mM) or low (14-17 mM) dialysate bicarbonate concentrations were utilized on separate days to either decrease or increase PH+, while plasma potassium concentrations (PK) were held at constant levels and changes in plasma renin activity (PRA) were minimized by avoiding changes in body weight. Changes in PH+ were associated with concordant changes in plasma aldosterone concentration (Pa) in both high- and low-bicarbonate studies. When these changes in Pa in high- and low-bicarbonate studies were analyzed together as a function of corresponding changes in PH+, a significant correlation could be demonstrated (r = 0.659, P less than 0.001). There was no correlation between changes in Pa and changes in PK, plasma sodium, plasma adrenocorticotropic hormone (ACTH), or PRA. Using the same methods to control PH+ and other variables during hemodialysis, the effects of altered PH+ on ACTH-stimulated aldosterone and cortisol secretion were evaluated in studies on six patients who received incremental infusions of ACTH after pretreatment with dexamethasone. In these studies, there was no demonstrable effect of PH+ on Pa or plasma cortisol concentration. We conclude that physiological changes in PH+ have a weak modulating effect on basal aldosterone secretion that may not be evident in the presence of other acutely applied stimuli.

Fetal and newborn cerebral vascular responses and adaptations to hypoxia.

I n the developing fetus and newborn infant, as in the adult, regulation of the cerebral circulation is unique in several regards. First, large arteries including the internal carotid, basilar, circle of Wilhs, and immediate branches of these vessels are important resistance vessels. It has been suggested that this arrangement helps to protect cerebral microvessels, and minimizes a vascular “steal” during localized blood flow increases in the brain. Also, cerebral vessels, particularly small arterioles and capillaries, possess a morphological and biochemical barrier between the blood and brain interstitial space. This blood-brain barrier is composed of a continuous endothelium, with tight junctions between adjacent cells. This biochemical barrier consists of high levels of degradative enzymes that prevent circulating neurotransmitters from gaining access to the brain. In addition, this barrier plays a key role in regulating cerebral vascular reactivity, as it does in other vascular beds. In response to physiological stimuli, such as acute hypoxemia, cerebral blood flow increases to maintain a normal rate of oxygen consumption and metabolism. During chronic hypoxia the flow responses exhibit adaptation in direct response to environmental circumstances. To establish some background for an understanding of the role of vascular endothelium in cerebrovascular regulation, we wiI1 first detail several “facts” and the problems associated with them. Fact. Many factors can affect blood flow to the brain and other organs, including changes in 02 and substrate availability, arterial CO, tension, extracellular hydrogen ion concentration, and extrinsic neurovascular influences (see Fig 1). These influences are integrated via homeostatic regulatory mechanisms that maintain brain 02 consumption and metabolism within a given region by altering cerebral vascular resistance. Problem. The question arises how this multitude of factors, both intrinsic and extrinsic to the cerebrovascular system, is orchestrated and integrated to result in precise regulation. Specifically, in regard to the fetus and newborn, to what extent do factors such as immaturity of the receptor populations and their coupling, vascular endothelium, or adrenergic innervation affect the responses? (As an aside, the various models proposed are not simple. Regulation is complicated by interactions and interdependence among many of the variables.) Fact. In the change at birth from fetus to newborn, a large number of cardiovascular, respiratory, hormonal, and metabolic changes occur that can influence cerebral blood flow regulation (see Table 1). Problem. In the face of this virtual physiologic “storm,” the question arises how these changes interact and are orchestrated or integrated to insure optimal function with maintenance of the matching between cerebral blood flow and cerebral metabolic rates. Fact. In response to acute hypoxia, a number of physiologic changes of the cardiovascular, respiratory, and endocrine systems occur. In response to chronic or long-term hypoxia, many different acclimatization responses take place (see Fig 2). Problem. The question arises how the fetus and newborn adjust and/or regulate cerebral blood flow, 02 consumption, etc, to compensate for acute and/or chronic hypoxia, and what role is played by the vascular endothelium in these adaptations. Fact. A number of clinical problems in the fetus and newborn infant occur as sequelae of dysregulation of blood flow to the brain, lungs, and other organs. Problem. A further question regards the means and to what extent the various regulatory factors, including the vascular endothelium, play a roIe in the genesis of these disorders.

Protonation of histidine groups inhibits gating of the of the quisqualate/kainate channel protein in isolated catfish cone horizontal cells

Increases in the extracellular hydrogen ion concentration ([H +] o) but not the intracellular concentration ([H +] i) antagonized the inward going membrane currents recorded from isolated cone horizontal cells during application of quisqualate, α-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid, and kainate. The pK determined from a titration curve was 6.5 with a slope greater than 1, indicating protonation of several histidines. The reduction in membrane current was voltage-independent. The affinity of the agonist for the receptor, the single-channel conductance, and the open time were unaffected by [H +] o· [H +] o antagonism was not the result of charge neutralization such as screening surface charge. Diethylpyrocarbonate, a histidine-modifying reagent, reduced the agonist-induced current, but disulfide- and sulfhydryl-modifying reagents were ineffective. These results suggest that histidine groups on the external face of the channel protein provide a functional site regulating channel gating.