ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01464.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Mammalian extramitochondrial pumps can be divided into two different classes: the vacuolar H+‐ATPases, which are responsible for acidification of intracellular compartments, and the E1E2‐type of ATPases, which are represented by the Na+,K+‐ATPase, the Ca2+‐ATPase and the gastric H+,K+‐ATPase. The latter enzyme is confined to the tubulovesicles and to the secretory membranes of the parietal cell and has been shown to be the proton pump of the gastric mucosa. The H+,K+‐ATPase carries out the electroneutral exchange of H+and K+and thereby generates a pH of less than 1 in the secretory canaliculus. For this process to occur, the enzyme must be activated by extracytosolic potassium ions. These ions reach the parietal cell luminal space by a secretagogue‐induced stimulation of a KCl pathway in the secretory membrane of the parietal cell. Kinetic studies in isolated ion‐tight and ion‐permeable gastric vesicles have shown that intravesicular K+stimulates the ATPase activity and accelerates the breakdown of the phosphorylenzyme intermediate formed during the catalytic cycle of the H+,K+‐ATPase.Thus the stimulation of the ATPase activity by K+is due to an increased rate of hydrolysis of phosphoenzyme. When the ATPase activity was analysed in permeable vesicles and at high K+concentrations, the ATPase activity was inhibited. In contrast, when the overall ATPase activity was analysed in ion‐tight vesicles, which developed an intravesicular positive potential in the presence of valinomycin, no inhibition of the ATPase activity was observed. This finding was interpreted as being due to the presence of a potential sensitive step in the K+‐limb of the enzyme cycle, as dissipation of the potential by the protonophore 3,3,4,5‐tetrachlorosalicylanilide (TCS) reinduced the K+inhibition. This observation indicated that, although the overall H+,K+‐ATPase transport cycle is electroneutral, intermediary steps such as the hydrogen and the potassium ion transport limbs are sensitive to potential, and ar

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01465.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Gastric parietal cells in primary culture have been tested to determine their utility as a model for the study of the role of intracellular calcium ([Ca2+]i) in the control of HCl secretion. Changes in [Ca2+]iwere measured in single cells on a microscope stage using the cell‐permeant form of the fluorescent calcium probe, fura‐2. Simultaneous images of cell fluorescence and morphology were acquired using a digitized video image analysis system and two video cameras, one for low‐light level fluorescence detection and one for high resolution DIC/transmitted light images. Both histamine and carbachol, which are known stimulants of HCl secretion, increased [Ca2+]iand stimulated dramatic changes in morphology in these cultured cells. Changes in morphology were accompanied by an increased uptake of the weak base, [14C]‐aminopyrine (AP), and a shift from green to red fluorescence of another weak base, acridine orange. These results indicate that cultured parietal cells, maintained under controlled conditions on a microscope stage, retain viability and secretagogue responsiveness. Thus, this cellular model appears to be suitable for correlation of changes in [Ca2+]iand activation of HCl se

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01466.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Stimulation of the gastric parietal cell requires massive membrane transformations as H+‐pumps from the domain of cytoplasmic tubulovesicles are recruited into the apical plasma membrane domain. The recycling of membrane pools, through fusion and fission processes that accompany stimulation and inhibition of HCl secretion, also involves highly selective events of protein incorporation and segregation. This manuscript describes several proteins that have been identified with the apical plasma membrane from maximally stimulated parietal cells, and broadly characterizes them either as permanent resident proteins of the apical membrane, or transient proteins that move into and out of the apical membrane as the cell progresses through the secretory cycle. A typical example of transient association with the apical membrane concerns the pump proteins, including the 94 kDa catalytic α‐subunit of the H+K+‐ATPase and its newly discovered β‐subunit glycoprotein, which move between tubulovesicles. Proteins that remain associated with the apical plasma membrane during rest and secretion include actin, and an 80‐kDa phosphoprotein, which has been variously called 80 K, ezrin, p81 and cytovillin, and whose phosphorylation is increased by the histamine/cAMP pathway of parietal cell stimulation. An example of a cytosolic protein that becomes associated with the apical plasma membrane after stimulation is a 120‐kDa protein, which appears to have protein kinase activity. Note that the identification, localization and characterization of the K+and Cl−transport proteins, which participate in net HCl secretion, are of immed

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01467.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Frog stomach transepithelial potential difference (Vt) and resistance (Rt), as well as the voltage divider ratio (VDR) and serosal membrane potential (Vs) of surface epithelial (SEC) and oxyntic (OC) cells were recorded at rest and during stimulation with histamine. Serosal membrane K+permeability was tested by sudden elevation of serosal K+concentration from 4 to 13 mmol l−1. Stimulation decreased bothVtandRtand increasedVDRof theOC(from 9.4 ± SD 3.0 to 14.4 ± 4.1,n= 10,P<0.001), whileVsremained virtually unchanged (‐66.3 ± 4.5 mV,n= 10); inSEC, however,VDRas well asVsincreased, the latter from −67.3 ± 5.9 to – 75.7 ± 7.3 mV,n= 9, P<0.001. Elevation of serosal K+reversibly diminishedVtandVSin both cell types. The transepithelial response to K+increased after stimulation. However, the cell potential response ΔVsKincreased only in the SEC (from +16.0 ± 2.9 to + 18.5 ± 2.6 mV,n= 9,P<0.001) but not significantly in theOC. We conclude that in frog stomach bothOCandSECare stimulated by histamine: theSECrespond with a hyperpolarization, which reflects an increase in their basolateral K+conductance: theOCdo not respond with a hyperpolarization, possibly because histamine increases the basolateral membrane K+conductance as well as other ion conductances which have not yet

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01468.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.The neutral proton pump (NP) model postulates a neutral exchange of K+for H+across the secretory membrane and the electrogenic proton pump (EP) model an electrogenic proton pump. Previous evidence is briefly reviewed and polarization of EMFs by transmucosal voltage clamping (VC) is presented. DuringVC, open circuit potential difference (PD) (VOC) is obtained by breaking the circuit for 2 s (after dielectric capacitors have discharged). The magnitude of polarization in Cl−media is less than in Cl−‐free media, presumably due to the high conductance of Cl−paths. The magnitude in Cl−‐free media is from 35 to 50 mV for aVCof 100 mV (nutrient side positive). The Na+/K+‐ATPase is not essential because with choline sulphate media polarization is typical. With Cl−‐free media,VOCversusIH(H+rate) is exponential but (VC ‐ VOC) versusIHis linear. Polarization on the basis of the NP model would be due to changes in K+diffusion potentials. However, with 80 mM K+on both sides (Cl−‐free media) polarization is typical. We conclude that polarization cannot be due to a change in K+diffusion potentials but to polarization of the EP model. The problem remains of how to incorporate the important finding of the H+/K+‐ATPase into a mo

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01469.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Many intracellular organelles contain a unique primary, electrogenic proton pump termed the vacuolar H+‐ATPase. This pump, found in many endocytic, secretory, and storage vesicles in fungal, plant and animal cells, functions, in conjunction with a chloride conductance, to acidify the vesicle interior. Although remotely related to the mitochondrial ATP synthase, the vacuolar H+‐ATPase is a distinct pump which differs in inhibitor sensitivity, subunit composition and function. The vacuolar H+‐ATPase transports only protons, and permeable anions (chloride) are required for optimal vesicle acidification. Allosteric and regulatory effects are not yet fully understood. Vesicle acidification appears to be essential for receptor‐mediated endocytosis, protein synthesis, and secretion and storage of small solutes such as neurotransmitters. A similar plasma membrane‐located H+‐ATPase may contribute to urinary acidification and cell pH

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01470.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.Ultrastructural studies performed on pigs revealed that numerous cytoplasmic tubulovesicles were present in resting pancreatic duct cells. Elevation of systemic arterial PCO2from 5.5 to 11 kPa increased the number of vesicles more than twofold. Following secretin administration, concurrent with the onset of HCO3−secretion (JHCO3). the cytoplasm became devoid of vesicles, and the basolateral plasma membrane surface area more than doubled. Similar phenomena were observed in bile duct cells. After pretreatment with the microtubulus‐inhibiting drug colchicine, secretin failed to reduce duct cell vesicle density, and JHCO3was reduced by c. 50% compared to the control. These ultrastructural changes resemble those described in other H+/HCO3−‐transporting organs such as the distal nephron and the urinary bladder. Our findings are compatible with the notion that cytoplasmic vesicles containing H+‐ATPases are incorporated into the basolateral plasma membrane of secretory cells during secretin stimulation. Active transport of H+into interstitial fluid might therefore be the driving force underly

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01471.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.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 par

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01472.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Abstract.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 HCO3actually enters cells in order to regulate int

ISSN:0954-6820    

DOI:10.1111/j.1365-2796.1990.tb01473.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY