Lansoprazole reverses Helicobacter pylori-inhibited gastric epithelial cell growth

Helicobacter pylori is associated with retarded healing and recurrence of peptic ulcer. Acid inhibitory agents, including proton pump inhibitors (PPIs), accelerate healing of peptic ulceration. Because epithelial cell proliferation is important for ulcer healing, we studied the effects of H. pylori and lansoprazole, a novel PPI, on gastric epithelial cell growth in vitro. Cell viability was significantly decreased when they incubated with 10(8) CFU/ml H. pylori. Nevertheless, all doses tested, from 10(6) to 10(8) CFU/ml H. pylori inhibited cell growth in a dose-dependent fashion. Co-incubation with AG-2000, an acid-converted derivative of lansoprazole, reversed H. pylori-inhibited cell growth. These results indicate that the antiulcer action of lansoprazole may involve a reversible effect on H. pylori-inhibited cell growth in addition to its well-established acid inhibitory action on parietal cells.

Effects of anti-ulcer agents on antibiotic activity against Helicobacter pylori

OBJECTIVE

To investigate the mechanism of action of a series of potential combination therapies for use against Helicobacter pylori.

DESIGN

The effects of certain anti-ulcer agents on the antimicrobial activity of antibiotics effective against H. pylori were determined in vitro.

METHODS

H. pylori was cultured on Skirrow's agar. Amoxycillin, clarithromycin, erythromycin and tetracycline were used. The anti-ulcer agents studied comprised aluminum chloride, sofalcone [2'-carboxymethyl 4,4'-bis(3-methyl-2-butenyloxy)chalcone] and zinc chloride. Urease activity was measured by the urease-indophenol method. The minimum inhibitory concentration was determined by a plating method, with H. pylori streaked on plates containing various concentrations of the antibiotics plus sublethal doses of the anti-ulcer agents.

RESULTS

This in vitro study showed that sofalcone had a direct antibacterial effect and, in addition, inhibited the adhesive property of H. pylori. It did not inhibit the antimicrobial activity of the antibiotics amoxycillin, clarithromycin, erythromycin or tetracycline against H. pylori. The metal ions had inhibitory effects on the antimicrobial activity of amoxycillin, erythromycin and tetracycline, but not on that of clarithromycin.

CONCLUSION

This study suggests that sofalcone is a suitable candidate for combination therapy.

Is phosphorylation the main physiological action of myosin light chain kinase?

The 155-kDa component of bovine stomach, which exhibits a strong actomyosin (AM) activating activity and a relatively weak myosin light chain kinase (MLCK) activity, has a strong affinity for the actin filament and the actin-binding site is confined to an 80 amino acid residue on its N-terminal side. This affinity may play a crucial role in AM activation. Some reagents preferentially abolish either the AM-activating effect or MLCK activity. In conclusion, MLCK of the 155-kDa component does not play a fundamental role in activating the AM system as far as the in vitro system is concerned. The possible mechanism of AM activation by the component is discussed.

Proliferative response of rabbit and rat gastric epithelial cells to human epidermal growth factor

The effect of human epidermal growth factor (hEGF) on gastric epithelial proliferation was studied in vitro and in vivo. In the first study, subconfluent gastric epithelial cells derived from fetal rabbit stomach were incubated with hEGF at doses of 0, 1, 10, 50, 100, 500 ng/ml and tritiated thymidine incorporation into DNA was determined. In the second study, fasted rats were given intraperitoneal injections of 100 micrograms/kg hEGF and ornithine decarboxylase activity was quantitated. In the third study, hEGF at doses of 0, 5, 10, 25, 50 micrograms/kg was administered perorally 3 times a day for 7 days. During the experiment, rats were allowed ad libitum intake of food and water. After 7 days, all rats were injected with tritiated thymidine 1 microCi/g body weight and sacrificed 1 h later. Sections from fundic and antral mucosae were processed for autoradiography. While hEGF stimulated tritiated thymidine incorporation into DNA by gastric epithelial cells in vitro, neither parenteral nor peroral administration of hEGF affected the proliferative measurements as assessed by ornithine decarboxylase activity or autoradiography in adult rat gastric fundic and antral mucosae in vivo. These results indicate that although hEGF has a direct proliferative effect on fetal rabbit gastric epithelial cells, exogenously administered hEGF has little effect on adult rat gastric mucosal steady state cell proliferation under physiological conditions.

Non-chemotactic Dictyostelium discoideum mutants with altered cGMP signal transduction

Folic acid and cAMP are chemoattractants in Dictyostelium discoideum, which bind to different surface receptors. The signal is transduced from the receptors via different G proteins into a common pathway which includes guanylyl cyclase and acto-myosin. To investigate this common pathway, ten mutants which do not react chemotactically to both cAMP and folic acid were isolated with a simple new chemotactic assay. Genetic analysis shows that one of these mutants (KI-10) was dominant; the other nine mutants were recessive, and comprise nine complementation groups. In wild-type cells, the chemoattractants activate adenylyl cyclase, phospholipase C, and guanylyl cyclase in a transient manner. In mutant cells the formation of cAMP and IP3 were generally normal, whereas the cGMP response was altered in most of the ten mutants. Particularly, mutant KI-8 has strongly reduced basal guanylyl cyclase activity; the enzyme is present in mutant KI-10, but can not be activated by cAMP or folic acid. The cGMP response of five other mutants is altered in either magnitude, dose dependency, or kinetics. These observations suggest that the second messenger cGMP plays a key role in chemotaxis in Dictyostelium.

[Digestion of human gastric mucous by extracellular Helicobacter pylori enzyme]

Helicobacter pylori (Hp) is a causative pathogen of chronic gastritis and strongly associated with recurrence of duodenal ulcers, but the mechanism is not known. We studied the possible digestion of gastric mucus by Hp extracellular enzyme in human stomach. Hp was isolated from biopsy specimens taken from peptic ulcer patients or normal individuals and its extracellular enzyme was collected. Incubation of human gastric mucosa with Hp extracellular enzyme resulted in a significant decrease of PAS-positive staining, indicating digestion of gastric mucus. Analysis of protein profile of extracellular enzyme revealed no difference among Hp strains. Subsequent zymography showed 2 bands; 97 K and 20 K, indicating existence glycosyl-hydrase. These results suggest that Hp weakens gastric mucosal defense by digesting carbohydrates in the protective mucus layer.

Effects of intracerebroventricular injection of indomethacin on adaptive gastric cytoprotection in the conscious rat

We investigated the role of prostaglandins in the central nervous system for the adaptive gastric cytoprotection in male Wistar rats with chronic intracerebroventricular cannulas. Three, 50, 200, or 500 micrograms of indomethacin or vehicle alone was injected via the intracerebroventricular (central) or intraperitoneal route 1 h before oral administration of 20% ethanol. The animals were then given 1 ml of absolute ethanol 15 min later. One hour later, gastric mucosal damage and plasma indomethacin concentrations were measured. Pretreatment with 50-500 micrograms of indomethacin abolished adaptive gastric cytoprotection induced by 20% ethanol in a dose-dependent fashion, regardless of the route of administration. Central administration of 3 micrograms indomethacin resulted in a more than twofold increase in mucosal damage compared with intraperitoneal administration. Plasma indomethacin concentrations were increased dose-dependently. However, plasma levels were lower in rats administered centrally than those peripherally at a dose of 50 micrograms indomethacin or more. On the other hand, plasma indomethacin concentrations did not differ between central and intraperitoneal administration of 3 micrograms indomethacin. Measurement of gastric mucosal blood flow revealed that central administration of 3 micrograms indomethacin reduced gastric mucosal blood flow, whereas intraperitoneal administration of an identical dose had no effect. These results suggest that central prostaglandins may contribute to adaptive gastric cytoprotection, possibly by altered gastric mucosal blood flow.

Effects of transforming growth factor alpha and beta on rabbit gastric epithelial cell proliferation: a preliminary report

The effects of epidermal growth factor (EGF), transforming growth factor alpha (TGF alpha), insulin-like growth factor-I (IGF-I), and transforming growth factor beta (TGF beta) on tritiated thymidine incorporation into DNA by rabbit gastric epithelial cells were investigated. EGF, TGF alpha, and IGF-I at concentrations of 10(-10) and 10(-9) M all produced a serum-like stimulatory effect, whereas TGF beta at both concentrations was inhibitory. Coadministration of TGF alpha had no additional effect on EGF-stimulated tritiated thymidine incorporation into DNA. On the other hand, coadministration of TGF beta abolished EGF-stimulated tritiated thymidine incorporation into DNA, suggesting possible interactions between the two growth factors.

The role of cyclic GMP in regulating myosin during chemotaxis of Dictyostelium: evidence from a mutant lacking the normal cyclic GMP response to cyclic AMP

Evidence has previously been reported that, during chemotaxis of the cellular slime mould Dictyostelium discoideum, cyclic GMP regulates the association of myosin II with the cytoskeleton and that this regulation is effected by inhibiting myosin II heavy chain phosphorylation (Liu and Newell, J. Cell Sci., 90, 123–129, 1988; 98, 483–490, 1991). Here we provide further evidence in support of this hypothesis using a mutant (KI-10) that is defective in chemotaxis and lacks the normal cyclic AMP-induced cyclic GMP response. We found that the cyclic AMP-induced cytoskeletal actin response was similar to that of the parental strain in this mutant (although showing a slight displacement in the dose-response curve) but the cytoskeletal myosin II heavy chain response was abolished. Moreover, the mutant showed no phosphorylation of myosin II heavy chain in response to cyclic AMP. Compared to the parental strain XP55, the mutant cells contained approximately 40% more protein and their doubling time was 30% longer. These differences could be due to differences in the efficiency of cell division, a process in which the proper regulation of myosin function is essential and in which cyclic GMP may therefore play a role.

Photoaffinity labeling of skeletal myosin with 2-azidoadenosine triphosphate

The purine binding site of ATP on skeletal muscle myosin has been photoaffinity labeled with 2-azidoadenosine diphosphate (2-N3ADP). 2-N3ADP was stably trapped at the active site (t1/2 approximately 5 days, 0 degree C) by complexation of the two heavy chain reactive thiols (Cys-697 and Cys-707) with Co(III)phenanthroline. Photoincorporation occurred only in the 23-kDa NH2-terminal tryptic fragment of the heavy chain. Extensive serial digestion of photolabeled subfragment 1 of myosin by trypsin and subtilisin yielded a series of labeled peptides which were purified by HPLC. Sequence and radiolabeling analysis of eight photolabeled peptides all indicated that tryptophan-130 was the only labeled residue. This site of labeling confirms earlier photolabeling studies with the non-nucleotide ADP analogue, 2[(4-azido-2-nitrophenyl)-amino]ethyl diphosphate (NANDP), which also labeled Trp-130 [Okamoto, Y., & Yount, R. G. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 1575-1579]. Comparison of the structures of 2-N3ADP and NANDP indicate that their azido groups can be superimposed if both analogues bind to the active site in an extended conformation in a manner analogous to the anti conformation of ATP.

Effects of prostaglandins on ornithine decarboxylase activity in rat small intestine

Role of prostaglandins on feeding-associated induction of ornithine decarboxylase in small intestine was studied. Rats received intraperitoneal injection of either saline, or 16,16-dimethyl prostaglandin E2, or TRY-200 (a stable prostaglandin I2 analog), or refeeding, after a 44 hr-fast. Four hours later, mucosae from duodenum, jejunum, and ileum were scraped for subsequent measurements of enzyme activity of ornithine decarboxylase by a radiometric technique. Refeeding resulted in a profound induction of enzyme activity throughout the small intestine. Parenteral administration of prostaglandin I2 also led to a significant induction with the level similar to refeeding. The stimulatory effect of prostaglandin I2 was completely abolished by a specific and irreversible enzyme inhibitor, difluoromethylornithine. Prostaglandin E2 had a similar but lesser effect than prostaglandin I2 on the induction of the enzyme activity. Pretreatment with indomethacin, a cyclooxygenase inhibitor had no effect on feeding-associated enzyme induction. These results indicate that although exogenous prostaglandin I2 appears to be a potent stimulant for ornithine decarboxylase activity in rat small intestine, endogenous prostaglandins seem to play little or no role in feeding-associated induction of ornithine decarboxylase.

Isolation of cDNA for bovine stomach 155 kDa protein exhibiting myosin light chain kinase activity

Two proteins with myosin light chain kinase activity and electrophoretic molecular weights of 155,000 and 130,000 were each isolated from bovine stomach smooth muscle [Kuwayama, H., Suzuki, M., Koga, R., & Ebashi, S. (1988) J. Biochem. 104, 862-866]. The 155 kDa component showed a much higher superprecipitation-inducing activity than the 130 kDa component, when compared on the basis of equivalent myosin light chain kinase activity. In this study, we isolated a cDNA for the entire coding region of the 155 kDa protein. The deduced amino acid sequence revealed a high degree of similarity to those of chicken and rabbit smooth muscle myosin light chain kinases. Multiple motifs, such as three repeats of an immunoglobulin C2-like domain, a fibronectin type III domain, and unusual 20 repeats of 12 amino acids were detected in the sequence. Part of the amino-terminal sequence was similar to that of the actin- and calmodulin-binding domain of smooth muscle caldesmon. These observations suggest that the 155 kDa protein has additional functions other than its enzymatic activity. Two mRNAs of 6.0 and 2.6 kb in length in the bovine stomach smooth muscle RNAs were hybridized with cDNA probes. The 2.6-kb RNA probably encodes telokin, which is the carboxyl terminus of smooth muscle myosin light chain kinase. mRNAs with identical lengths were also detected in bovine aorta.

Effects of prostaglandins on hydrocortisone-induced delayed healing of chronic gastric ulcers in the rat

We have previously shown that chronic steroid administration delays the healing of experimental gastric ulcers in rats. This study was designed to test the beneficial effects of 16,16-dimethylprostaglandin E2 or TRY-200, a stable prostaglandin I2 analogue, on the delayed healing by hydrocortisone (HC) of chronic gastric ulcers in rats. Chronic gastric ulcers were produced in male Wistar rats, weighing 180 g, by serosal application of 100% acetic acid. The rats were randomly divided into six groups: (1) saline, (2) saline, HC-treated, (3) 10 micrograms/kg of 16,16-dimethylprostaglandin E2, (4) TRY-200, a stable prostaglandin I2 analogue, at 5 micrograms/kg, or (5) 10 micrograms/kg, or (6) 30 micrograms/kg. All rats, except for control, were given daily intraperitoneal injection of 2.5 mg/kg of HC sodium phosphate. Tested drugs were administered intragastrically twice a day for 2 weeks. Rats were killed 14 days later and ulcer size was measured. Chronic administration of HC sodium phosphate resulted in a significant delay of ulcer healing induced by acetic acid. Treatment with TRY-200 at 10 or 30 micrograms/kg abolished the deleterious effect of steroids, whereas 16,16-dimethylprostaglandin E2 had no effect. These results indicate that prostaglandin I2 is more effective than prostaglandin E2 in reversing the delayed healing by steroids of chronic gastric ulcers in the rat.

Effects of sucralfate, lansoprazole, and cimetidine on the delayed healing by hydrocortisone sodium phosphate of chronic gastric ulcers in the rat

We have previously shown that chronic sucralfate ingestion stimulates gastric epithelial proliferation in rats, which may explain one of the beneficial effects of sucralfate in healing of peptic ulcers. In a separate study, we have found that chronic steroid administration delays the healing of experimental gastric ulcers in rats. This study was designed to test the beneficial effects of sucralfate, cimetidine, and lansoprazole (AG-1749, a new proton pump inhibitor), on the delayed healing by steroids in rat chronic gastric ulcers. Chronic gastric ulcers were produced in male Wistar rats, weighing 180 g, by the application of 100% acetic acid. The rats were randomly divided into five groups; (1) control, (2) vehicle alone, (3) 10 mg/kg lansoprazole, (4) 500 mg/kg sucralfate, and (5) 100 mg/kg cimetidine. Except for controls, all rats received daily intraperitoneal injections of 2.5 mg/kg hydrocortisone sodium phosphate. Tested drugs were administered intragastrically (lansoprazole and sucralfate) or intraperitoneally (cimetidine) twice a day for 2 weeks. Rats were sacrificed 14 days later and ulcer size was measured. Chronic administration of hydrocortisone sodium phosphate resulted in a significant delay of ulcer healing induced by acetic acid. Treatment with either lansoprazole or sucralfate abolished the deleterious effect of steroids, whereas cimetidine had no effect. These results indicate that lansoprazole and sucralfate overcome the delayed healing by steroids of chronic gastric ulcers in the rat.

A rapid, accurate, immunohistochemical method to label proliferating cells in the digestive tract. A comparison with tritiated thymidine

A rapid immunohistochemical method using 5'-bromo-2'-deoxyuridine (BrdU), a thymidine analog, for labeling proliferating epithelial cells was modified and tested for accuracy against standard tritiated thymidine autoradiography (3H-TdR) in rat esophagus, stomach, duodenum, and colon. Either BrdU or 3H-thymidine or both compounds (simultaneously) were injected IP. Histological sections of these tissues were immunostained with monoclonal anti-BrdU antibody, linked to horseradish peroxidase by standard avidin-biotin techniques and stained with diaminobenzidine, or sections were dipped for autoradiography, or both techniques were applied to the same tissue section. Results showed that (a) BrdU labeled the same number of proliferating cells in all organs as 3H-TdR; (b) BrdU colabeled with 3H-thymidine; (c) immunostaining was complete in 3-4 days but standard 3H-TdR took 2 weeks; and (d) qualitative analysis took 50% less time with BrdU than with standard 3H-TdR.

Roles of the amino acid side chains in the actin-binding S-site of myosin heavy chain

The heptapeptide Ile-Arg-Ile-Cys-Arg-Lys-Gly-OEt is the analog of the S-site, one of the actin-binding sites in myosin [Suzuki et al. (1987) J. Biol. Chem. 262, 11410-11412]. Various substituted heptapeptides were synthesized, and the dissociation constants of each acto-heptapeptide complex was measured. Comparison of the dissociation constants indicated that the hydrophobic side chain of Ile-1 was critical for the binding with F-actin, but not that of Ile-3. The positive charge and the side chain length of Arg-2 were also important. The presence of a sulfur atom in the Cys-4 was also necessary. The affinity of the N-terminal Ile-Arg-Ile part for F-actin was influenced by the kind of residues in the C-terminal tetrapeptide part. Based on these results, the side chains of Ile(702), Arg(703), and Cys(SH1)(705) in myosin subfragment-1 heavy chain were assigned to be critical for the binding with F-actin. The amino acid sequence of S-1 heavy chain containing these critical residues for the S-site from residue number 700 to 717 can be predicted as an analogue of the segment B of the ATP-binding site [Walker et al. (1982) EMBO J. 1, 945-951]. The actin-binding S-site possibly shares a part of the ATP-binding site in myosin. We discuss the possibility that the S-site is an inhibitory site of myosin ATPase and the so-called actin-activation of myosin ATPase is a deinhibition induced by transient binding of F-actin to the S-site.

[Clinical significance of gastrointestinal hormone]

Gastrointestinal hormones have been used for diagnostic and therapeutic applications. Although it is assumed that gastrointestinal hormones may be involved in many diseases of the gut. So far, however, we can identify significant roles only in peptic ulcer disease, syndromes caused by gastrointestinal hormone-producing tumors, chronic pancreatitis, and sprue. Future investigation will make the role of gastrointestinal hormone clearer in many diseased states.

Effects of single parenteral indomethacin injection in rat fundic and antral epithelial proliferation

To study the effects of a single parenteral dose of indomethacin on gastric epithelial proliferation, we performed the following study. Male Wistar rats weighing about 200 g were divided into two groups and given single intraperitoneal injections of indomethacin 5 mg/kg, either suspended in 0.5% carboxymethyl cellulose sodium salt or vehicle alone, after an overnight fast. After 6 h, all rats were injected by tail vein with tritiated thymidine, 1 microCi/g body weight, to label proliferating cells and were killed 1 h later. Sections from fundic and antral mucosae were processed for light autoradiography. Parenteral indomethacin resulted in spotty erosions in fundic mucosa. Histologically, there was congestion with or without epithelial disruption. These areas were excluded in the proliferation measurements. There was a significant decrease not only in the number of labeled cells but also in the thickness of the proliferative zone with the thinning of the entire mucosal thickness in the fundic mucosa. None of the measurements in antral mucosa showed significant difference. These results showed that a single parenteral injection of indomethacin inhibits epithelial proliferation and decreases mucosal thickness in fundic, but not antral mucosa of the rat.

The effect of the replacement of ADP with a photoaffinity ATP analogue, 2-azido-ADP, in F-actin on its function

2-Azido-ATP, a photoaffinity ATP analogue, was incorporated into actin and the influence of the incorporation on the actin function was studied. The replacement of ADP with 2-azido-ADP in F-actin both before and after photocross-linking decreased appreciably the actin-activated S1-ATPase activity. Photocross-linked 2-azido-ADP-F-actin could be depolymerized by dialysis against a solution containing 0.1 mM CaCl2, 0.1 mM ATP and 1 mM Tris-HCl (pH 8.0). However, once it depolymerized, it lost very quickly the ability to polymerize even in the presence of a sufficient amount of ATP and Ca2+.

Effects of water-immersion restraint stress on rat gastric epithelial cell loss and migration

The effect of water-immersion restraint stress on cell loss and migration was studied in rats. In order to label the proliferating cells, tritiated thymidine was injected 72 h prior to the stress. Histoautoradiography was prepared for the measurement of cell migration and residual mucosal DNA-bound radioactivity by means of liquid scintillation count for cell loss. Residual DNA-bound radioactivity was significantly decreased in fundic mucosa, but not in antral mucosa, after 60-90 min of water-immersion restraint stress. Cell migration was also found to be accelerated in fundic mucosa after 90 min of stress. These results indicate that water-immersion restraint stress results in an increase of cell loss, which is accompanied by compensated acceleration of cell migration, in fundic mucosa of rats before the development of gastric erosions. In view of the previous observation that stress for the same short-term duration inhibits fundic epithelial proliferation in rats, this combination, increased cell loss with depressed epithelial proliferation, may contribute to stress-related gastric mucosal lesions in rats.

Isolation from bovine brain of 155 kDa component exhibiting myosin light chain kinase activity

1) Taking myosin light chain kinase (MLCK) activity as the index, bovine extract was fractionated by the use of anion-exchange chromatography, cation-exchange chromatography, and calmodulin affinity chromatography. The kinase activity of the fraction thus obtained was elevated up to about 12,400 times over that of the original crude extract. 2) The fraction mentioned above was subjected again to anion exchange chromatography. The kinase activities were divided into two parts, i.e., part I which contained the 155 kDa component and part II which was virtually free of 155 kDa component. The MLCK activity of part I was considerably lower than that of part II. 3) Part I was subjected to gel filtration using AcA 34 gel and the 155 kDa component was isolated. The fraction contained the 155 kDa component in a homogeneous state and showed myosin specific kinase activity, which was about 2 X 10(5) times that of the original crude extract. 4) The high kinase activity of part II seemed to be ascribable to the 130 kDa component, in accord with the report of Hathaway, Adelstein, and Klee (J. Biol. Chem. 256, 8183-8189, 1981).

Preparation of protein components exhibiting myosin light chain kinase activities from bovine aorta: discrepancies between its enzyme activity and actomyosin activating effect

1) Two protein components, 155 and 130 kDa in their electrophoretic molecular weights, respectively, were isolated in a homogeneous state from bovine aorta; they showed both the superprecipitation-inducing effect on desensitized natural actomyosin and the myosin light chain kinase (MLCK) action on gizzard myosin. 2) The superprecipitating activity of the 155 kDa component was 5 time higher than that of the 130 kDa component on the basis of equivalent MLCK activity. 3) The same procedure was applied to bovine stomach, giving rise to a 155 kDa component in a homogeneous state as in the case of aorta, but the 130 kDa component thus prepared was contaminated by higher molecular weight components. 4) If compared on the basis of equivalent MLCK activity, bovine stomach 155 kDa component showed more than 10 times higher superprecipitating activity than the fraction that contained the 130 kDa component as the main constituent. 5) The discrepancy between the superprecipitating activity and MLCK activity mentioned above was discussed in relation to the Ca2+ regulation mechanism in smooth muscle contraction. The possibility that the 130 kDa component might be a proteolytic product of the 155 kDa component was also discussed.

Effects of parenteral hydrocortisone sodium succinate on epithelial renewal in hamster gastric mucosa

The aim of this study was to determine whether parenteral administration of steroids affects epithelial renewal in hamster stomach. Male golden hamsters received either hydrocortisone sodium succinate or saline intraperitoneally for three days. In the first experiment, hamsters were sacrificed 1 hr after injection of tritiated thymidine [( 3H]TdR) to label proliferating cells. In the second experiment, hamsters were sacrificed hourly after a single [3H]TdR injection up to 48 hr in order to determine cell cycle time by the method of fraction of labeled mitoses. In the third experiment, hamsters were sacrificed 1, 24, and 72 hr after [3H]TdR injection for the study of epithelial migration and cell turnover time. Sections of fundic and antral mucosae were prepared for light autoradiography. Steroid treatment caused no gross or microscopic injury to gastric mucosa, but the number of [3H]TdR-labeled cells as well as the thickness of the proliferative zone were reduced significantly in fundic mucosa, but not in antral mucosa. The study of the fraction labeled mitoses indicated that steroid treatment lengthened the cell cycle time in fundic mucosa, which was due primarily to prolonged G1 and DNA synthesis phases. Furthermore, epithelial migration was significantly slower in fundic mucosa after steroid treatment, which was associated with a prolonged cell turnover time. Thus, parenteral steroids depress the entire process of epithelial renewal in hamster fundic mucosa.

The membrane potential modulates the ATP-dependent Ca2+ pump of cardiac sarcolemma

The effect of membrane potential on the activity of the ATP-dependent Ca2+ pump of isolated canine ventricular sarcolemmal vesicles was investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K+, and the initial rates of Ca2+ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca2+ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K+ channel blocker, tetraethylammonium ion or Ba2+. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca2+ pump is suggested from the increase of Ca2+ uptake by negative potential induced by valinomycin.