De-confusing the THOG problem: the Pythagorean solution.

Sources of facilitation for Needham and Amado's (1995) Pythagoras version of Wason's THOG problem were systematically examined in three experiments with 174 participants. Although both the narrative structure and figural notation used in the Pythagoras problem independently led to significant facilitation (40-50% correct), pairing hypothesis generation with either factor or pairing the two factors together was found to be necessary to obtain substantial facilitation (> 50% correct). Needham and Amado's original finding for the complete Pythagoras problem was also replicated. These results are discussed in terms of the "confusion theory" explanation for performance on the standard THOG problem. The possible role of labelling as a de-confusing factor in other versions of the THOG problem and the implications of the present findings for human reasoning are also considered.

Adulthood relocation: implications for personality, future orientation, and social partner choices.

The purpose of this study was to learn the reasons why individuals relocate and whether relocaters differ from nonrelocaters on demographic, social, and personality factors. One hundred participants from three age groups, 34 to 46 (young/middle-aged), 54 to 66 (young-old), and 69 to 93 (older) years, were designated as relocaters or residents as a function of months of residence. Relocaters did not differ from residents in age, income, health, or marital status. Reasons provided for relocating revealed the following differences: young/middle-aged moved for employment reasons, young-old moved for reasons of retirement, and older adults relocated to be closer to family members. No differences in network size occurred and older relocaters selected more cards in a social partner selection task. Most interesting was the finding that relocaters scored higher on Openness to Experience and future orientation. These data suggest personality may be an important trait that explains why some individuals are more likely to relocate.

Elementary, my dear Wason: the role of problem representation in the THOG task.

The present study was concerned with Wason's THOG problem, a hypothetico-deductive reasoning task for which performance over the past 20 years has typically been very poor (< 20% correct). We examined the hypothesis that incorporating a quasi-visual context into the problem statement would make both the binary, symmetric tree structure and solution principle of the THOG task clearer and thus facilitate performance. A version of O'Brien et al.'s (Q J Exp Psychol 42A:329-351) Blackboard THOG problem, that specifies each branch of the tree by describing a specific location for each possible color-shape combination, was used to test this hypothesis. Substantial facilitation was both observed (68% correct) and replicated (73% correct), and it was also shown that it is necessary to provide a representation of both sides of the tree to obtain this level of facilitation. The implications of these results for human deductive reasoning are considered.

Differential expression of canalicular membrane Ca2+/Mg(2+)-ecto-ATPase in estrogen-induced and obstructive cholestasis in the rat.

Extracellular adenosine triphosphate (ATP) may regulate hepatocyte and cholangiocyte functions, and under some conditions it may have deleterious effects on bile secretion and cause cholestasis. The canalicular membrane enzyme Ca2+/Mg2+-ecto-ATPase (ecto-ATPase) hydrolyzes ATP/adenosine diphosphate (ATP/ADP) and regulates hepatic extracellular ATP concentration. Changes in liver ecto-ATPase in estrogen-induced cholestasis were examined in male rats receiving 17alpha-ethinylestradiol (E groups) for 1, 3, or 5 days (5 mg/kg/day, sc) and compared with changes in rats subjected to obstructive cholestasis (O groups) for 1, 3, or 8 days. Activity of ecto-ATPase, protein mass in canalicular membranes and bile (estimated by Western blotting), steady state mRNA levels (by Northern blotting), and cellular and acinar distributions of the enzyme (histochemistry and immunocytochemistry) were assessed in these groups. Activity of ecto-ATPase, protein mass in isolated canalicular membranes, and enzyme mRNA levels were significantly increased in E group rats as compared with controls. In contrast, these parameters were markedly decreased in O group rats, and the enzyme protein was undetectable in bile. The ecto-ATPase histochemical reaction was markedly increased in the canalicular membrane of E group rats, extending from acinar zone 2 to zone 1, whereas it decreased in the O group. The ecto-ATPase immunocytochemical reaction was present in the canalicular membrane and pericanalicular vesicles in control and E group hepatocytes, but it decreased in obstructive cholestasis and was localized only to the canalicular membrane. Thus, significant changes in liver ecto-ATPase were apparent in 17alpha-ethinylestradiol-induced cholestasis that were opposite to those observed in obstructive cholestasis. Assuming that the alterations observed in obstructive cholestasis are the result of the cholestatic phenomenon, we conclude that changes in ecto-ATPase in 17alpha-ethinylestradiol-treated rats might be either primary events or part of an adaptive response in 17alpha-ethinylestradiol-induced cholestasis.

Development of the actin and the cytokeratin cytoskeletons of parietal cells during differentiation of the rat gastric mucosa.

Available evidence strongly suggests that microfilaments and cytokeratin intermediate filaments (IF) play a role in the reorganization of the luminal pole required for the secretion of acid by parietal cells. To correlate the organization of both cytoskeletal systems with the differentiation of the secretory membranes of parietal cells, the distribution of F-actin and cytokeratin was studied during the ontogenic development of the rat. Primitive parietal cells were detected with parietal cells autoantibodies and ultrastructurally by transmission electron microscopy (TEM). The distribution of IF and of F-actin in differentiating parietal cells was determined using anticytokeratin antibodies and FITC-phalloidin, respectively. Development of both cytoskeletal systems was followed by TEM. Ultrastructurally, parietal cells are identified from day 19 on, by the presence of an incipient canaliculus, which later enlarges and fills with microvilli. No intracellular tubulovesicular system is observed. Using parietal cells autoantibodies these cells are detected from day 20 on. Immunocytochemistry and TEM demonstrate that parietal cells possess organized cytokeratin and actin cytoskeletons, which develop further as differentiation proceeds. At birth, parietal cells show an ultrastructure and a distribution of IF and microfilaments similar to that of differentiated cells. In newly born rats, the F-actin cytoskeleton redistributes after suckling. This reorganization results from an enlargement of the canalicular lumen, filled with microvilli rich in actin. Thus, functional maturation of parietal cells is paralleled by the development of organized IF and F-actin cytoskeletons associated to the secretory surface.

Effects of diosgenin, a plant-derived steroid, on bile secretion and hepatocellular cholestasis induced by estrogens in the rat.

Increased biliary secretion of cholesterol and lipid vesicles (unilamellae and multilamellae) induced by diosgenin (D), a plant-derived steroid, has cytoprotective effects in the rat liver subjected to obstructive cholestasis. In this study, our aims were to investigate the following: 1) the effects of D on the bile secretory process and on the cholestasis induced by estradiol-17beta-(beta-D-glucuronide) (E17G) or 17 alpha-ethynylestradiol (E) administration; 2) whether the potentially protective effects of D are related to D-induced increase of biliary cholesterol and lipid lamellae; and 3) whether D has other effects capable of modifying specific bile secretory processes or preventing the cholestatic effects of estrogens. Rats were fed a standard ground chow (control group) or chow containing D for 6 days. E17G was administered i.v. to control and D-fed rats and bile flow, bile salt output, and alkaline phosphatase excretion were examined. 17alpha-E was administered from days 4 to 6 to rats fed standard chow or chow plus D for 6 days and different functional parameters of the bile secretory process as well as the ultrastructure of hepatocytes and histochemistry of alkaline phosphatase and Mg2+-adenosine triphosphatase (ATPase) were examined. D-treatment markedly increased cholesterol and lamellar structures in bile and attenuated the acute cholestatic effects of E17G. D-feeding prevented the decrease of taurocholate maximum secretory rate and the increase of biliary alkaline phosphatase and Ca2+,Mg2+-EctoATPase (EctoATPase) excretion, as well as the increase of cholesterol/ phospholipids ratio, alkaline phosphatase activity, and EctoATPase content in canalicular plasma membranes induced by E. D-feeding did not prevent E-induced decrease of basal bile flow, bile salt, cholesterol, and phospholipid secretory rates nor the decrease of Na+,K+-ATPase activity and Na+-taurocholate cotransporting polypeptide (Ntcp) content in isolated sinusoidal membranes. Cholestatic alterations of canalicular domain were apparent in E-treated rats. D administration was also associated with changes of ultrastructure and histochemistry of hepatocytes. E-induced alterations in ultrastructure and acinar distribution and intensity of histochemical reaction of both enzymes were partially prevented by D-feeding. We conclude that D administration, in addition to inducing a marked increase of biliary cholesterol and lipid lamellar structures output, was associated to changes in hepatocyte morphology and plasma membrane composition, enzymes activity, and histochemistry. D-feeding attenuated the acute cholestatic effects of E17G. D-induced increase of bile cholesterol and lipid lamellae content was not apparent when D-fed rats received E. Despite this fact, D administration prevented some cholestatic effects of E, probably through different metabolic effects and/or direct membrane effects, not related to increased lipid lamellae excretion.

Isolation of intact organelles by differential centrifugation of digitonin-treated hepatocytes using a table Eppendorf centrifuge.

A quick subcellular fractionation procedure using differential centrifugation, which is applicable to isolated and cultured cells, is presented. This technique was developed for studying the subcellular localization of phosphorylated proteins in isolated liver cells after various stimuli, but is also applicable to many other situations. The main difference with the usual techniques is that by including digitonin in the homogenization buffer, the procedure is greatly shortened. Furthermore, because the soluble fraction is separated from the particulate fraction very early in the fractionation procedure, subcellular organelles are not exposed to phosphatases and other soluble enzymes such as esterases and proteases during the fractionation. The entire procedure is carried out in an Eppendorf centrifuge, which allows isolation of the cytosolic fraction in less than 1 min, a washed nuclear fraction in about 4 min, a mitochondrial fraction in less than 10 min, and a washed light mitochondrial L fraction in about 40 min. Judging by the behavior of marker enzymes and the morphology of the fractions, the method is highly comparable to classical procedures.

Modulation of hepatic content and biliary excretion of P-glycoproteins in hepatocellular and obstructive cholestasis in the rat.

BACKGROUND/AIMS: Release into bile of canalicular membrane enzymes, such as alkaline phosphatase and gamma-glutamyl transpeptidase, is significantly increased in rats subjected to experimental models of hepatocellular or obstructive cholestasis. This effect appears to be related to a greater susceptibility of these membrane intrinsic proteins to the solubilizing effects of secreted bile acids. It is not known whether canalicular membrane transport proteins, such as P-glycoprotein isoforms, involved in ATP-dependent xenobiotic biliary excretion and phospholipid secretion, are excreted into bile and whether this process is modified in cholestasis. The aims of this work have been to investigate in the rat: a) whether P-glycoproteins are normally excreted into bile, b) whether their excretion is modified in two experimental models of cholestasis, i.e., hepatocellular cholestasis induced by ethynylestradiol and obstructive cholestasis, and c) whether observed changes correlate with bile acid and phospholipid secretion and enzyme release into bile and with relative P-glycoprotein content in hepatic tissue and isolated and purified canalicular membranes. METHODS: P-glycoproteins in bile and hepatic tissue were identified and quantitated by Western-blotting and immunohistochemistry using the C219 MAb. Changes in total mdr mRNA were analyzed by Northern-blotting. RESULTS: Like canalicular membrane enzymes, P-glycoproteins are normally excreted into bile. Ethynylestradiol-induced cholestasis was associated with a 4.9-fold increase in P-glycoprotein excretion compared with controls while, in contrast, the excretion of the carrier decreased markedly in obstructive cholestasis to 2% of control values. P-glycoprotein excretion per nmol of secreted bile acids increased 4.4-fold in ethynylestradiol-induced cholestasis but decreased to 2% of control values in obstructive cholestasis. Total mdr mRNA levels in hepatic tissue were markedly increased (3.4-fold) in rats subjected to obstructive cholestasis and moderately increased (1.6-fold) in the ethynylestradiol group, compared with controls. P-glycoprotein content in isolated canalicular membranes was slightly decreased by 15% in ethynylestradiol-induced cholestasis, while it increased 4.7-fold in obstructive cholestasis. Immunohistochemistry of rat livers showed that P-glycoprotein reaction at the canalicular domain of hepatocytes at acinar zone 1 was decreased in ethynylestradiol-treated rats and markedly increased in obstructive cholestasis. CONCLUSIONS: Ethynylestradiol-induced cholestasis is associated with increased P-glycoprotein biliary excretion and decreased hepatic content. In contrast, obstructive cholestasis results in decreased P-glycoprotein biliary excretion and increased hepatic content. These results suggest that biliary P-glycoprotein excretion might be a modulating factor in canalicular membrane P-glycoprotein content. Increased P-glycoprotein release into bile in ethynylestradiol-treated rats is apparently not a consequence of cholestasis, but it might be a primary event and play a pathogenetic role in ethynylestradiol-induced cholestasis.

Association of canalicular membrane enzymes with bile acid micelles and lipid aggregates in human and rat bile.

This study was undertaken to gain insights into the characteristics of the polymolecular association between canalicular membrane enzymes, bile acids, cholesterol and phospholipids in bile and into the celular mechanisms whereby the enzymes are secreted into bile. With this purpose, we studied the distribution of bile acids, cholesterol, phospholipids, proteins and representative canalicular membrane enzymes (alkaline phosphatase, 5'-nucleotidase and gamma-glutamyl transpeptidase), which can be considered specific marker constituents, in bile fractions enriched in phospholipid-cholesterol lamellar structures (multilamellar and unilamellar vesicles) and bile acid-mixed micelles. These fractions were isolated by ultracentrifugation from human hepatic bile, normal rat bile and bile of rats treated with diosgenin, a steroid that induces a marked increase in biliary cholesterol secretion, and were characterized by density, lipid composition and transmission electron microscopy. These studies demonstrate that alkaline phosphatase, 5'-nucleotidase and gamma-glutamyl transpeptidase are secreted into both human and rat bile where they are preferentially associated with bile acid-mixed micelles, suggesting a role for bile acids in both release of these enzymes and lipids from the canalicular membrane and solubilization in bile. In addition, heterogeneous association of these enzymes with nonmicellar, lamellar structures in human and rat bile is consistent with the hypothesis that processes independent of the detergent effects of bile acids might also result in the release of specific intrinsic membrane proteins into bile.

Parietal cells contain most of the myosin, filamin and actin present in rat gastric glands.

The association of myosin and a filamin-like protein to the F-actin cytoskeleton of parietal cells was studied in the rat gastric mucosa. Myosin and the filamin-like protein were localized by indirect immunofluorescence microscopy while the distribution of actin was established by using FITC-phalloidin. These cytoskeletal proteins, concentrated in the parietal cells, changed their distribution in correlation with the hydrochloric acid (HCl) secretory state of the cells and the appearance of a developed intracellular canaliculus. Thus, in resting parietal cells, actin showed a patchy distribution, delimiting the poorly developed secretory canaliculi, while myosin and the filamin-like protein distributed diffusely over the cytoplasm. In secreting cells, F-actin was concentrated in the cytoplasmic projections filling the canalicular lumen, while myosin and the filamin-like protein were excluded from this region, concentrating in the adjoining cytoplasm. The present results show that myosin and the filamin-like protein change their association with the secretory membranes in relation to the development of the secretory canaliculus of parietal cells. In resting cells, both proteins associate with the endocellular secretory membranes. In secreting cells, the microvillar projections of the canalicular surface formed by these membranes bind F-actin, but exclude myosin and the filamin-like protein.

Differentiation of oxyntic cells and cell-matrix interactions during avian gastric gland morphogenesis.

The relation between the expression of the oxyntic cell phenotype and the modifications of the extracellular matrix during development of the gastric glands, was studied in 10 to 21 day-old chick embryos. Cytodifferentiation of the oxyntic cells was established by ultrastructural methods, while the expression of pepsinogen, mitochondrial enzyme markers and apical secretory membranes was determined by histochemical and biochemical procedures. Results show that the morphogenesis of the glandular lobules occurs between days 8 and 15 of gestation. Later on, the lobules enlarge but maintain their basic morphology. Until day 13, the developing glands consist of primary tubes lined by a stratified columnar epithelium. The apical poles of the cells that contact the lumen show cytoplasmic processes, and Mg-ATPase activity and F-actin are concentrated at the apical cell borders. From day 13 on, the cells of the simple epithelium that lines secondary tubules budding from the primary tube, show all the features that define differentiated oxyntic cells. The synthesis of glycosaminoglycans during glandular morphogenesis was studied measuring the incorporation of radioactive sulfate into developing chick embryo proventriculi. An important increase in isotope incorporation was found between days 13 and 18 of development. Histochemical localization of these macromolecules shows that glycosaminoglycans are closely associated with the developing glandular lobules. Variations in the structure of epithelial cells undergoing morphogenesis and in the composition of the extracellular matrix are synchronous, suggesting that interactions between them may be significant in terms of the establishment and maintenance of the adult gastric gland phenotype.

A lipid-anchored heparan sulfate proteoglycan is present in the surface of differentiated skeletal muscle cells. Isolation and biochemical characterization.

We have investigated the presence of hydrophobic membrane-associated heparan sulfate proteoglycans (HSPG) on the cell surface of differentiated skeletal muscle cells. A HSPG releasable by incubation with a phosphatidylinositol-specific phospholipase c (PtdIns-PLC) was obtained. HSPG were also isolated from Triton X-100 extracts of the cells. The hydrodynamic characteristics of the PtdIns-PLC-releasable and detergent-extracted HSPG were indistinguishable. SDS/PAGE analysis of the PtdIns-PLC-releasable HSPG indicated a molecular mass of 250 kDa. Analysis of proteins immunoprecipitated by specific antibodies against a HSPG isolated from Schwann cells demonstrated that the antisera precipitated an intact HSPG that was present in the pool of proteins released by PtdIns-PLC and by Triton X-100 from [35S]sulfate labeled cells. Nitrous acid degradation of the immunoprecipitated proteins released by PtdIns-PLC from [35S]methionine labeled cells produced a single 67-kDa core protein. Analysis of hydrophobicity of the purified HSPG revealed that only the HSPG obtained from the detergent extract were able to be incorporated into the liposomes whereas the PtdIns-PLC-released HSPG was not. Immunocytolocalization analysis of the differentiated cells indicated that the PtdIns-PLC-releasable HSPG was located on the cell surface. Prior incubation of the cells with PtdIns-PLC significantly reduced the surface staining. Analysis of skeletal-muscle sections of adult rat skeletal muscles indicated that this HSPG localized exclusively at the endomysium. This localization suggest that these HSPG may be acting as a cell receptor for extracellular-matrix (ECM) components.

Isolation of peroxisomes from frozen human liver samples.

This paper shows the successful isolation of peroxisomes from human liver samples that were kept frozen at -70 degrees C. Purification of these peroxisomes was obtained by a combination of two subcellular fractionation techniques: differential centrifugation and isopycnic fractionation in Nycodenz density gradients. Peroxisome integrity was evaluated by latency measurements and by ultrastructural observation. The procedure described here may be useful for the isolation of other subcellular organelles from frozen human samples.

Redistribution of membranes and cytoskeletal proteins in chicken oxyntic cells during the HCl secretory cycle: ultrastructural and immunofluorescence study.

Changes in ultrastructure and cytoskeletal organization by avian oxyntic cells, at the onset of HCl secretion, were analysed. Cells in resting state, induced by fasting and cimetidine, were compared with histamine stimulated secreting cells. Ultrastructural studies were done by transmission electron microscopy; the distribution of prekeratin, myosin, and filamin-like protein, by immunofluorescence; and that of F-actin using FITC-phalloidin. Resting cells show short pericellular clefts. These are increasingly deepened in secreting cells by a reorganization of the lateral cell borders involving displacement of the junctional complexes toward the cell base and incorporation of the tubular system to the luminal plasma membrane. In secreting cells, the processes of the secretory surface are concentrated in a pericellular groove. Histamine stimulation induces a drastic redistribution of cytoskeletal proteins. In chicken oxyntic cells, in addition to the F-actin cytoskeleton associated with the membranes of the secretory surface, there is a cytoskeletal ring containing F-actin, myosin, and a filamin-like protein, located at the level of the junctional complexes. In resting cells, filaments and masses of cytoskeletal matrix are associated with the zonula adherens. In secreting cells, the junctional complexes maintain their association with the filamentous ring, while the amorphous matrix is replaced by microfilaments that support the processes of the luminal surface. Intermediate filaments form a peripheral ring probably associated with the zonula adherens, and project from the ring toward the cell cytoplasm. Thus, with the onset of HCl secretion, the apical cytoskeletal ring of resting cells displaces toward the cell base. A role for this cytoskeletal ring in the changes in shape parallel to HCl secretion is discussed.

Distribution of intermediate filaments in epithelial cells of the amphibian urinary bladder: an immunofluorescence study.

The distribution of intermediate filaments in toad and frog urinary bladder was studied on frozen sections by indirect immunofluorescence microscopy using specific antiprekeratin antibodies. Our results show that in both species, epithelial cells lining the urinary bladder are very rich in cytokeratin, organized as a filamentous network. In granular cells, the most abundant cells facing the urinary lumen, vasopressin promotes fusion of the membranous tubular structures located in the luminal cytoplasm with the apical cell membrane. A role for intermediate filaments in the membrane rearragements induced by vasopressin in these cells, is proposed.

Quantitative subcellular study of apical pole membranes from chicken oxyntic cells in resting and HCl secretory state.

Vertebrate oxyntic cells, responsible for gastric HCl production, undergo a remarkable morphological reorganization in relation to their secretory cycle. In resting state, the luminal surface of the cells is smooth; a peculiar system of endocellular membranes, the tubular system, occupies the luminal cytoplasm. Actin filaments frame a cortical network between the tubular system and the luminal plasma membrane. With the onset of HCl secretion, the tubular system becomes incorporated into the luminal plasma membrane. Villous processes containing microfilaments fill the secretory surface. This morphological reorganization of membranes and cytoskeletal matrix could regulate HCl secretion by translocation of membranes containing the proton pump from the endocellular compartment to the secretory surface. In this paper, we describe the isolation of membranes that selectively belong to the tubular system or to the cytoplasmic processes of the secretory surface of chicken oxyntic cells. Chicken oxyntic cells are the main cellular component of the proventricular glands. A resting state was obtained after cimetidine treatment, whereas the HCl-secretory state was induced by histamine. We present a comparative analysis of resting and stimulated chicken gastric glands by quantitative subcellular fractionation. The HCl secretory state was related to specific modifications in membrane fractions derived from the secretory pole of oxyntic cells. Morphological and functional reorganization of oxyntic cells was closely correlated with changes in: the sedimentation pattern of the marker enzyme of the apical pole membrane (K-NPPase), the total activity of K-NPPase and nonmitochondrial Mg-ATPase, the valinomycin dependence of K-ATPase, and polypeptides that cosediment in purified membrane fractions. Changes in the distribution pattern of K-NPPase after fractionation of histamine-stimulated glands were consistent with the replacement of the small vesicles typical of resting glands by dense membrane profiles, analogous to the luminal processes of stimulated oxyntic cells. SDS-PAGE showed that, in purified membrane fractions of stimulated glands, the concentration of 28-, 43-, and 200-kD polypeptides increased while that of 95- and 250-kD polypeptides decreased. The present results define the tubular system of oxyntic cells as an organelle with properties different from those of endoplasmic reticulum, mitochondria, and plasma membrane. The biochemical and physico-chemical properties of this membraneous system changed when the organization of the membranes and the cytoskeletal matrix of the apical pole was modified by the onset of HCl secretion.

Filamin and myosin are present in the secretory pole of amphibian oxyntic cells. An immunofluorescence study.

The presence of a filamin-like protein in oxyntic cells was established by indirect immunofluorescence microscopy. The location of this protein and myosin was studied, using specific antibodies, on frozen sections and isolated cells. Antifilamin and antimyosin reacted strongly with the luminal cytoplasm of the cells. In resting oxyntic cells, filamin appeared organized as a reticular sheet in the apical border. In stimulated cells, the apical concentration of filamin decreased, and its distribution appeared rather diffuse. This immunoreactive band seems to correspond to the cytoplasmic region where actin microfilaments have been described previously. The changes in the apical concentration of filamin, induced by the onset of HCl secretion, correlate with the ultrastructural reorganization of the actin network that occurs during the secretory cycle. The use of antimyosin antibodies showed that this protein forms an apical peripheral ring in both resting and stimulated cells. No clear changes in the distribution of myosin, in relation to secretion, could be established by immunofluorescence. These findings, taken together with published morphological and biochemical evidence, suggest that a three-dimensional network composed of actin and filamin is present in the secretory pole of resting amphibian oxyntic cells. The hypothesis that gel-sol transitions play a role in the structural reorganization of the secretory pole of these cells is supported by the present results.

Redistribution of gastric K+-NPPase in vertebrate oxyntic cells in relation to hydrochloric acid secretion: a cytochemical study.

Gastric K+-NPPase represents a partial reaction of the (K+-H+)ATPase system, which is considered to be the proton pump in mammalian parietal cells. In the present paper, K+-NPPase activity was cytochemically studied by the method of Mayahara et al. (1980) in gastric glands of birds, amphibia, and mammals, either in the resting state induced by cimetidine or after stimulation of HCl secretion by histamine. The gastric K+-NPPase cytochemical reaction was localized only in oxyntic cells of the gastric mucosa in the three species tested. The subcellular distribution of the K+-NPPase reaction product drastically changes with the secretory state of HCl. In resting cells, the K+-NPPase staining is associated with the membranes of the endocellular tubular system while in HCl-secreting cells, it is associated with the plasma membrane of the elaborate secretory surface characteristic of this functional state. The above results demonstrate that the same enzymatic activity, which is associated with the gastric proton pump, is present in both membranous systems of the oxyntic cell secretory pole. This fact supports the proposal that the tubular system represents a membrane reserve that inserts the proton pump into the luminal plasma membrane in vertebrate oxyntic cells under the action of HCl secretagogues.

Intermediate filaments of the cytoskeleton in glandular cells of the rat fundic mucosa: immunofluorescence and electron microscopy study.

The organization of intermediate filaments (IF) in cells of the rat fundic mucosa was studied by electron microscopy and immunofluorescence microscopy using specific antiprekeratin antibodies on frozen sections and isolated cells. Our results suggest that mucous cells lining the gastric surface and the gastric pits, which appeared strongly decorated, are the most rich in IF. These cells displayed coarse bundles of IF oriented in all directions as well as desmosome-attached tonofibrils. Mucous neck cells contained fewer bundles of IF located preferentially toward the apical region. Zymogen cells showed a strong staining along the contour of the luminal border, together with a faint decoration of a fine meshwork extending throughout the cytoplasm. A poorly defined fibrillar cortex present underneath the secretory plasma membrane and sparse bundles of IF among the elements of the rough endoplasmic reticulum were seen in thin sections. In contrast, parietal cells appeared brightly stained and the prekeratinlike material formed a cortical polygonal meshwork especially visible in isolated cells. A developed system of IF formed by conspicuous bundles located underneath the secretory canaliculi, among the mitochondria and in the vicinity of the basal plasma membrane, was observed in the electron microscope.