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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Saliva was collected from the mandibular glands of anaesthetized common wombats (Vombatus ursinus) to ascertain maximal flow rates, salivary composition and possible adaptations, particularly PO4(3-) secretion, to assist digestion. After temporary catheterization of the main duct through its oral opening, salivary secretion was evoked at flow rates ranging from 0.02 +/- 0.002 (+/- SEM) ml.min-1 (0.7 +/- 0.07 microliter.min-1.kg body weight-1) to 0.4 +/- 0.05 ml.min-1 (14 +/- 1.9 microliters.min-1.kg body weight-1) by ipsilateral intracarotid infusion of acetylcholine. The [Na+] (15 +/- 5.1 to 58 +/- 8.6 mmol.l-1) and [HCO3-] (35 +/- 1.9 to 60 +/- 1.9 mmol.l-1) were positively correlated with salivary flow rate. The [K+] (58 +/- 5.2 to 30 +/- 2.4 mmol.l-1), [Ca2+] (10.4 +/- 1.67 to 4.1 +/- 0.44 mmol.l-1), [Mg2+] (0.94 +/- 0.137 to 0.17 +/- 0.032 mmol.l-1), [Cl-] (71 +/- 9.2 to 45 +/- 6.0 mmol.l-1), [urea] (9.3 +/- 0.79 to 5.1 +/- 0.54 mmol.l-1), H+ activity (29 +/- 1.6 to 17 +/- 1.6 nEq.l-1) and amylase activity (251 +/- 57.4 to 92 +/- 23.3 mu kat.l-1) were negatively correlated with flow. Both concentration and osmolality fell with increasing flow at the lower end of the flow range but osmolality always increased again by maximal flow whereas the relation between protein and flow was not consistent at the higher levels of flow and stimulation. Salivary [PO4(3+)] was not correlated with flow and at 3-14% of the plasma concentration was extremely low.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Secretion of electrolytes, protein and urea by the mandibular gland of the common wombat (Vombatus ursinus). 773 31

In the present publication we report mainly electrophysiological studies on oxyntopeptic cells of frog gastric mucosa which aim at clarifying a possible involvement of these cells in the process of resting gastric alkali (HCO3-) secretion, described in the preceding publication. The experiments were performed on intact gastric fundus mucosa of Rana esculenta mounted in Ussing chambers. After removal of the muscle and connective tissue layer oxyntopeptic cells were punctured from the serosal surface with conventional or pH-sensitive microelectrodes to measure, besides transepithelial voltage and resistance, the basolateral cell membrane potential, the voltage divider ratio, and the cell pH in response to secretagogues and/or changes in serosal ion concentration. Carbachol (10(-4) mol/l), which transiently stimulated HCO3- secretion by 0.22 mumol.cm-2.h-1, transiently acidified the cells by 0.09 +/- SEM 0.03 pH units (n = 6) and transiently induced an apical cell membrane anion conductance. According to the model of gastric HCO3- secretion presented in the preceding publication, this anion conductance could be involved in gastric HCO3- secretion, mediating, besides Cl- efflux, also apical HCO3- efflux. In addition carbachol stimulated basolateral Na+(HCO3-)n-cotransport, which according to the results from the preceding publication mediates basolateral HCO3- uptake for secretion. By contrast, cAMP-mediated secretagogues, such as histamine or others, which stimulate HCl secretion and transiently alkalinize the oxyntopeptic cells, were found to down-regulate the basolateral Na+(HCO3-)n-cotransporter.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Model of bicarbonate secretion by resting frog stomach fundus mucosa. II. Role of the oxyntopeptic cells. 783 89

Unfertilised mouse oocytes absorbed the pH-sensitive fluoroprobe SNARF-1-AM (carboxyseminaph-thorhodafluor-1-acetoxymethylester), the ester being hydrolysed by an intracellular esterase. Ratio-imaging of oocytes containing the resultant SNARF-1 excited by laser light (514 nm) has been obtained by scanning confocal microscopy with appropriate barrier filters to monitor emission maxima about 590 and 640 nm recorded simultaneously in separate channels of the framestore. Images produced by pixel-by-pixel division of these channel images showed uniform distribution of SNARF-1 in equatorial regions in most cells. However, in some oocytes regions (about 4 microns diameter) with smaller ratios (i.e. lower pHi) were detected. The relation between the ratio of emitted maxima and the extracellular pH (pHo) in the presence of nigericin allowed a calibration procedure to determine the intracellular pH (pHi). With this method pHi was estimated to be 7.13 +/- 0.05 (mean +/- SEM, n = 31). Whereas the application of a weak acid (butyric) caused a fall in the ratio and hence in pHi, exposure to weak bases (NH4Cl or trimethylamine) caused a rise. Large changes in pHo did not evoke corresponding changes in the ratio and hence in pHi. Addition of 5% CO2 to the external solution buffered at the usual value of pH 7.4, however, did cause a fall in the ratio which was reversible only when HCO3- was present in the external solution.
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PMID:Confocal ratio-imaging of intracellular pH in unfertilised mouse oocytes. 788 14

In the present experiments we have made a new attempt to characterize the ion transport properties of H(+)-secreting cells of the gastric mucosa using electrophysiological techniques. Individual gastric glands of bullfrog fundus mucosa were manually dissected, mounted in holding pipettes and superfused with various test solutions while individual cells were punctured with conventional or H(+)-sensitive double-barrelled microelectrodes. All measurements were performed in the resting state (0.1 mmol/l cimetidine). In HCO3(-)-containing control Ringer solution the cell membrane potential (Vb) averaged -45.6 +/- 0.9 mV (+/- SEM, n = 54). From the fast initial Vb responses to changing bath K+, Na+, Cl- or HCO3- concentrations we deduced that the basolateral cell membrane contains conductances for K+, Na+, and Cl- but not for HCO3-, and that a Na(+)-HCO3- cotransporter is not present. The K+ conductance was inhibited by Ba2+ (3 mmol/l), but the Cl- conductance was not inhibited by 4,4' diisothiocyanato-stilbene-2,2' disulphonic acid (DIDS, 0.3 mmol/l), nor selectively inhibited by 5-nitro-2-(3)- phenylpropyl-aminobenzoate (NPPB, 10 mumol/l). In a great number of cells the Vb response to Cl- substitution revealed two components: an initial spiking depolarization which reflected conductive Cl- efflux and a secondary slow hyperpolarization, the origin of which was not immediately evident. Since the latter response could be mimicked by CO2-free perfusion, strongly depressed by Ba2+ and eliminated by DIDS, we conclude that it reflects HCO3- uptake into the cells via a DIDS sensitive Cl-/HCO3- exchanger which alkalinizes the cells and stimulates the basolateral K+ conductance. Our results confirm, revise and extend the results of previous, less direct, investigations of gastric cell ion transport.
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PMID:Electrophysiological investigation of microdissected gastric glands of bullfrog. I. Basolateral membrane properties in the resting state. 789 5

Following the technical approach described in the preceding publication we have investigated if, and how, stimulation of gastric HCl secretion affects the basolateral ion transport properties of oxyntopeptic cells of Rana catesbeiana stomach. To this end microdissected gastric glands were punctured with conventional or H(+)-sensitive glass microelectrodes and the effects of changing bath ion concentrations on the cell membrane potential (Vb) and cell pH (pHi) were determined. Except for a transient alkalinization, histamine (0.5 mmol/l) did not significantly affect Vb or pHi. The latter averaged 7.18 +/- 0.03 (mean +/- SEM, n = 5) under resting conditions (0.1 mmol/l cimetidine) and 7.21 +/- 0.07 (n = 5) in the presence of histamine. In addition, neither the initial velocity nor the final steady-state value of the cell alkalinization following a 10:1 reduction of bath Cl- concentration changed in the presence of histamine, and the same holds true for the cell acidification following a 10:1 reduction of bath HCO3- concentration. These observations indicate that the basolateral Cl-/HCO3- exchanger was not stimulated by histamine, and that no other base transporters were activated. By contrast, the Vb response to elevation of bath K+ concentration decreased, and so did the initial depolarizing Vb response to bath Cl- substitution, while the secondary hyperpolarizing response increased. The latter observations are compatible with the notion that stimulation by histamine reduced a pH-insensitive part of the basolateral K+ conductance and reduced also the basolateral Cl- conductance.
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PMID:Electrophysiological investigation of microdissected gastric glands of bullfrog. II. Basolateral membrane properties in the presence of histamine. 789 6

The effects of beta-adrenergic agonists on pHi were studied on single ventricular myocytes isolated from adult rat heart and loaded with the acetoxymethyl ester (AM) form of the pH indicator SNARF-1. In modified Krebs' solution containing 20 mmol/L HEPES and 4.4 mmol/L HCO3-, isoproterenol (1 mumol/L) caused a significant decrease of steady-state pHi from 7.20 +/- 0.02 to 7.13 +/- 0.02 (mean +/- SEM) within 2 minutes. This acidification, which was also observed in myocytes that were preloaded with the Ca2+ chelator BAPTA and superfused with nominally Ca(2+)-free solution, was blocked by propranolol as well as by the specific beta 1-antagonist CGP 20712 A but not by the beta 2-antagonist ICI 118,551. Forskolin (10 mumol/L) induced a similar reversible decrease of pHi (average decrease, 0.11 +/- 0.02 pH unit). Furthermore, adenosine (100 mumol/L) substantially attenuated the isoproterenol-induced decrease of pHi. The effect of isoproterenol was not prevented by inhibitors of the Na(+)-H+ antiport, amiloride (1 mmol/L) and 2-N,N-hexamethylene amiloride (20 mumol/L). On the other hand, blockers of Cl- transport mechanisms, DIDS (200 mumol/L) and probenecid (100 mumol/L), inhibited this acidification, Isoproterenol also failed to induce a decrease of steady-state pHi in myocytes incubated in Cl(-)-free medium. Rather, the initial rate of rise of pHi observed on removal of external Cl- ions was significantly increased in the presence of isoproterenol or dibutyryl cAMP. Because the alkalinization induced by removal of Cl- ions is mainly due to reversal of the Cl(-)-HCO3- exchanger, the augmentation of this initial rate of pHi rise directly points to a beta-adrenergic stimulation of the exchanger. Furthermore, the pHi recovery following NH4Cl exposure was accelerated by isoproterenol in the presence of probenecid, indicating that the Na(+)-HCO3- cotransport and/or the Na(+)-H+ antiport also could be activated.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Chloride dependence of pH modulation by beta-adrenergic agonist in rat cardiomyocytes. 792 32

We have previously demonstrated (M. Stubbs, Z. M. Bhujwalla, G. M. Tozer, L. M. Rodrigues, R. J. Maxwell, R. Morgan, F. A. Howe, and J. R. Griffiths, NMR Biomed., 5: 351, 1992) that the intracellular pH (pHi) of several rat tumors is higher (> pH 7.0) than that of the tumor extracellular fluid (pHe), in contrast to normal tissues (e.g., liver) in which pHi is lower than pHe. In this paper we confirm a pHe of 6.8 +/- 0.07 (SEM) in Morris hepatoma 9618a by an independent method and report the tissue content of other ions by both 31P magnetic resonance spectroscopy and by conventional analysis in hepatomas and livers in rats. Compared with liver, tissue Na+ was 2-fold higher and tissue K+ was lower. Tissue Ca2+ was 8-fold higher (7.4 +/- 4.3 mumol/g wet weight) and tissue Pi was 2-fold higher (8.5 +/- 1.3 mumol/g wet weight) suggesting the presence of insoluble calcium phosphate. Cl- was unchanged (approximately 40 mumol/g wet weight), whereas HCO3- was lower in the hepatoma (12.4 +/- 0.83 compared to 15.5 +/- 0.76 mumol/g wet weight). Total tissue Mg2+ was similar in both tissues, but free [Mg2+] (calculated by two different methods) was approximately 5-fold lower in the hepatoma. The ATP values were 3.5-fold and [NAD]/[NADH] 9-fold lower in the hepatoma. The results are compatible with the hypothesis that the chronic partial hypoxia of tumor tissue involves changes in the linked equilibria of many ions and metabolites and may help explain such pathologies as calcification.
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PMID:Metabolic consequences of a reversed pH gradient in rat tumors. 803 32

The effect of picomolar concentrations of angiotensin II (AII) was investigated in isolated perfused rabbit renal proximal tubules using conventional or pH-sensitive intracellular microelectrodes. Under control conditions cell membrane potential (Vb) and cell pH (pHi) averaged -53.8 +/- 1.9 mV (mean +/- SEM, n = 49) and 7.24 +/- 0.01 (n = 10), respectively. AII (at 10(-11) mol/l), when applied from the bath (but not when applied from the lumen perfusate), produced the following effects: approximately 85% of the viable tubules responded with a small depolarization (+5.5 +/- 0.4 mV, n = 43) which was accompanied in half of the pHi measurements by a slow acidification (delta pHi = -0.03 +/- 0.01, n = 5). The remaining 15% responded with a small hyperpolarization (delta Vb = -3.1 +/- 0.4 mV, n = 6). All changes were fully reversible and repeatable. Experiments with fast changes in bath HCO3 or K concentrations, as well as measurements of the basolateral voltage divider fraction in response to transepithelial current flow, explain these observations as stimulation of a basolateral Na-HCO3 cotransporter and of a basolateral K conductance. Both counteract in their effect on Vb, but can be individuated by blocker experiments with 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and barium. Both the stimulation of Na-HCO3 cotransport and the stimulation of the K conductance may result from down-regulation of the level of cyclic adenosine monophosphate in the cell.
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PMID:An electrophysiological study of angiotensin II regulation of Na-HCO3 cotransport and K conductance in renal proximal tubules. I. Effect of picomolar concentrations. 805 63

In the first part of our study, we described the effect of picomolar concentrations of angiotensin II (AII) on cell membrane potential (Vb) and cell pH (pHi) of isolated perfused rabbit renal proximal tubules. In the present publication we summarize respective observations with micromolar concentrations of AII. With a few exceptions nearly all experiments showed mirror-image-like results. In the majority of the experiments 10(-6) mol/l AII, when applied from the bath (but not when applied from the lumen), slightly hyperpolarized the cells by -3.4 +/- 0.3 mV (mean +/- SEM, n = 20) and alkalinized them by up to 0.06 pH units, while the lower AII concentrations, which were applied in the previous study, depolarized and acidified. The present observations suggest that micromolar concentrations of AII inhibit basolateral Na-HCO3 cotransport. This conclusion was confirmed by a decreasing Vb response to step changes of basolateral HCO3 concentration. In addition, there was a tendency of the Vb response to K concentration steps to decrease, but measurements of the voltage divider ratio did not point to a significant inhibition of a basolateral K conductance. In spite of the almost perfect reciprocity of the results with 10(-6) and 10(-11) mol/l AII, some specific observations suggest that micromolar concentrations of AII do not simply cause mirror-image-like effects, but influence still further transport systems compared to picomolar concentrations.
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PMID:An electrophysiological study of angiotensin II regulation of Na-HCO3 cotransport and K conductance in renal proximal tubules. II. Effect of micromolar concentrations. 805 64

This study aimed to assess the suitability of sheep tracheal epithelium as a model for studies of human airway ion transport. Ovine and human airway epithelium were mounted in Ussing chambers under short circuit conditions. Bumetanide (100 microM) reduced short-circuit current (Isc) by a mean of 21.3% +/- SEM 2.0, n = 8, in sheep, and 30.4% +/- 9.7, n = 3, in human airway epithelium. Acetazolamide (100 microM) decreased Isc by 10.6% +/- 1.2, n = 18, in sheep, and 5.8% +/- 2.9, n = 3, in human airways. Phloridzin (200 microM) reduced Isc by 4.7% +/- 0.8, n = 7, and 3.1% +/- 5.1, n = 3 in sheep and human tissue respectively. Amiloride (100 microM) decreased Isc by 42.9% +/- 3.5, n = 12, in sheep airways, whilst bathing the mucosal surface with Na(+)-free solutions reduced Isc by 67.4% +/- 4.2, n = 18. The sequential addition of acetazolamide, bumetanide, phloridzin, amiloride and mucosal Na(+)-free solutions totally inhibited the basal Isc in both sheep and human tissues, suggesting that Cl- and HCO3- secretion, Na(+)-glucose co-transport and amiloride-sensitive and -insensitive Na+ absorption contribute to the Isc. The similarities between the species suggest that sheep tracheal epithelium is a useful model for basal studies of airway ion transport, and may prove a valuable tool for further regulatory studies.
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PMID:Characterization and comparison of ion transport across sheep and human airway epithelium. 819 65


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