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D H Malinowska

Publications and source records attributed to D H Malinowska.

36 records · Page 2Linked to original sources
PubMed1988

Gastric H+ secretion: histamine (cAMP-mediated) activation of protein phosphorylation.

Activation of H+ secretion by the gastric parietal cell involves major changes in morphology, metabolic activity and ion pathways of the secretory membrane. These changes are elicited by histamine binding to the H2 receptor, raising cAMP levels and presumably activating cAMP-dependent protein kinase. Concomitantly, the intracellular free Ca2+ concentration, [Ca2+]i, increases. Studies were performed to determine whether cAMP-mediated protein phosphorylation accompanies histamine activation of H+ secretion and to catalogue the major protein species serving as substrates for cAMP-dependent protein kinase in the parietal cell. 80% pure rabbit parietal cells, prepared by Nycodenz bouyant density centrifugation, were used. To investigate only cAMP-mediated effects, histamine-dependent changes in [Ca2+]i in these cells were abolished by depleting intracellular Ca2+ stores and performing experiments under Ca2+-free conditions. Acid secretion and steady-state levels of protein phosphorylation were then measured in unstimulated (cimetidine-treated) and histamine-stimulated cells. In intact parietal cells, concommitant with histamine stimulation of H+ secretion, increases in the level of protein phosphorylation were observed. Significantly changing phosphoproteins found in supernatant fractions showed apparent subunit sizes of approx. 148, 130, 47 and 43 kDa, and in microsomal fractions included those at approx. 130, 51 and 47 kDa. In parietal cell homogenates, using [gamma-32P]ATP, cAMP elicited significant phosphorylation of eight supernatant proteins and twelve microsomal proteins, which included the histamine-dependent phosphoproteins found in the intact parietal cell, except for the 51 kDa microsomal protein. As a working hypothesis, these proteins are involved in stimulus-secretion coupling in the parietal cell.

Animals↗
PubMed1988

Cytoskeletal determinants of control of gastric acid secretion.

Isolated purified parietal cells from rabbit gastric mucosae were used to investigate the functions of phosphoproteins associated with regulation of acid secretion. These cells responded well to secretagogues, increasing their level of acid secretion by ca. four-fold. Stimulation of acid secretion was accompanied by a distinct morphological change, which involves the cytoskeletal system of the parietal cell, particularly the microfilaments, as evidenced by potent inhibition of secretion by cytochalasin E. Parietal cells contained several actin binding proteins, at least one of which (47 kD) had a similar molecular weight as a previously identified stimulus-related phosphoprotein. A single 130 kD parietal cell protein was immunoreactive with anti-vinculin monoclonal antibody, correlating with another previously identified stimulus-related phosphoprotein. The functional role of these proteins may be to link the microfilaments with the secretory membrane, an important step in the generation and/or maintenance of the stimulated state of acid secretion in the parietal cell.

Actin Cytoskeleton↗
PubMed1985

CSF-brain permeability in the immature sheep fetus: a CSF-brain barrier.

The permeability of the neuroependyma between CSF and brain extracellular space has been studied in fetal sheep of 60 and 125 days gestation. Both radioactive ([3H]inulin, [14C]sucrose, [125I]albumin) and visible (horseradish peroxidase) markers have been perfused through the ventricular system for periods of up to 5 h in anaesthetized exteriorized fetal sheep whose physiological condition was monitored continuously. A previously undescribed barrier between CSF and brain extracellular fluid has been discovered in the immature (60-day) fetal sheep. Horseradish peroxidase penetration was confined to a limited depth of the neuroependyma and was mainly into the cells lining the cerebral ventricles; in older fetuses there was extracellular penetration to a distance of several millimetres from the ventricular surface, as previously described in adult animals. The volumes of distribution of sucrose and insulin were less in the immature brain than in the more mature brain, which may be a reflection of restricted diffusion across the neuroependyma in the younger brains. The morphological nature of the barrier in fetuses of 60 days and younger appears to be a membrane specialization between the cells of the neuroependyma. It is of a type not previously described; it seems to have the effect of narrowing rather than obliterating the extracellular pathway between CSF and brain. The possible functional significance of this observation is discussed.

Animals↗
PubMed1984

Cellular mechanisms of acid secretion.

Current ideas about the parietal cell are presented in the model shown in Figure 6; the cell is illustrated both in resting and stimulated states. The basal-lateral surface contains three major receptor classes mediated by either cyclic AMP responses or Ca2+ changes, Ca2+ channels and a Ca2+ pump, and a variety of ion transport pathways such as Na+:H+ and Cl-:HCO-3 exchange, a K+ conductance, a postulated NaKCl2 cotransport and the (Na+ + K+)ATPase. At rest, the tubulovesicles contain the (H+ + K+)ATPase. In the stimulated state, the apical (secretory canalicular) membrane contains a K+ and Cl- conductance as well as the (H+ + K+)ATPase. There is also a change in cytoskeletal arrangement associated with stimulation.

Animals↗
PubMed1983

Cl- requirement of acid secretion in isolated gastric glands.

The dependence of acid formation, as measured by aminopyrine (AP) accumulation, on medium and intracellular Cl- was investigated in resting (10(-4) M cimetidine) and stimulated (10(-3) M dibutyryl cAMP) gastric glands isolated from the rabbit stomach. Intracellular Cl- concentrations (Cli-) were measured by the steady-state distribution of 36Cl-. In Cl- -free conditions AP accumulation was absent. Medium Cl- induced AP accumulation (AP ratio = 125) in stimulated glands with a K0.5 of 10.4 +/- 1.1 mM, equivalent to 18.0 +/- 1.2 mM Cli-, and had a small effect on resting glands (AP ratio = 6). With normal Nai+ and Ki+ maintained, similar results were obtained in stimulated glands treated with 10(-5) M amphotericin (ampho) and 10(-4) M ouabain (ouab), where the basal-lateral membrane was confirmed to be short-circuited with respect to Cl- pathways, i.e., medium Cl- and Cli- were equal. The K0.5 for Cl-i was 17.5 +/- 2.5 mM. In resting glands treated with ampho and ouab, AP accumulation increased linearly (no saturation was observed) with increasing Cl- (AP ratio = 35). These results suggest that stimulation activates a Cl- component in the secretory membrane and not in the basal-lateral membrane of the parietal cell. The K+ requirement of AP accumulation at a physiological Cl-i of 60 mM was also investigated in ampho- and ouab-treated glands. On stimulation the K0.5 for Ki+ decreased from 19.5 to 12 mM, coupled with a large increase in AP accumulation, indicating that stimulation also activates a K+ component in the secretory membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1981

Properties of the gastric proton pump in unstimulated permeable gastric glands.

It was found that digitonin-permeabilized resting gastric glands retained considerable acid-secretory ability. Oligomycin abolished this, and ATP was able to bypass this inhibition and restore acid secretion. Moreover, the effect of anoxia was also bypassed by ATP in these preparations. As in intact glands, acid secretion was K+ dependent, and the concentration for half-maximal effect was 18.5 +/- 1.76 mM in Na+-free solutions, a value similar to that found for resting intact glands. The slight inhibition of ATP-dependent secretion by either valinomycin or 2,4-dinitrophenol, but total inhibition by a combination of the ionophores, is interpreted to mean that, in resting gastric glands, the in situ proton pump is electroneutral and the KCl pathway supplying K+ to the luminal face of the pump is probably electroneutral.

Acid-Base Equilibrium↗
PubMed1981

Plasma proteins in fetal sheep brain: blood-brain barrier and intracerebral distribution.

1. Plasma proteins have been demonstrated to be present in early fetal sheep brain in amounts which cannot be accounted for by blood contamination. 2. The distribution of alpha-fetoprotein, albumin, fetuin, alpha 1-antitrypsin and transferrin has been studied by immunoassay of extracts from brain homogenates and by immunoperoxidase histochemistry of fetal brains between 37 and 125 days gestation (term is 150 days). 3. At 35 days gestation fetuin and albumin were quantitatively the most important proteins in fetal brain, both as estimated by extraction and by immunohistochemistry. Both of these proteins, and also alpha-fetoprotein and alpha 1-antitrypsin, declined considerably in amount by 60 days gestation. After 60 days the concentrations of albumin and alpha-fetoprotein were not significantly different from that due to blood contamination and only occasional cells could be demonstrated by immunohistochemistry. Fetuin and alpha 1-antitrypsin were present in reduced but significant amounts at least up to 125 days gestation. 4. The immunohistochemical results showed that considerable numbers of immature neurones were stained for some plasma proteins. Fetuin positive cells predominated both in terms of the larger number of cells which stained at 35-40 days gestation and in the persistence of positive cells up to 125 days gestation. Numerous cells in the neuroependymal layer and in several layers of the developing cortical plate were positive, especially early in gestation. Only a few transferrin or alpha 1-antitrypsin positive cells were observed. 5. Permeability of the blood-brain barrier to sheep or human serum albumin (labelled with 125I) was tested in 60 day fetal sheep by intravenous injection and estimation of brain radioactivity at 3 or 6 hr with allowance for blood contamination. Only a very small (but significant) penetration of protein was detected. Unlike penetration of protein into c.s.f. at the same age, it did not reach its natural steady state in brain. 6. It is concluded that the blood-brain barrier to protein is well developed in the immature fetal sheep but that developing neurones probably acquire certain plasma proteins directly from the c.s.f. when they are differentiating in the neuroependyma. The subsequent distribution of plasma protein positive cells in different brain regions is suggested to be due to the migration of developing neurones for the neuroependyma although the possibility of local synthesis of plasma proteins has not been excluded.

Albumins↗
PubMed1980

Proteins in cerebrospinal fluid and plasma of fetal sheep during development.

1. The concentration of total protein in c.s.f. and plasma has been measured in fetal sheep of different gestational ages and in the adult. In c.s.f. it was highest (approximately 840 mg/100 ml.) in the youngest fetuses (35 days) and declined steeply by 60 days (260 mg/100 ml.). It decreased less markedly in the last half of gestation to reach about 50 mg/100 ml. at 125 days which is twice the adult value. Protein concentration in plasma was lowest in the youngest fetuses and did not rise much until the second half of gestation during which time it doubled. There was a further rather larger increase between the late fetal (125 days) stage and the adult.2. Albumin, fetuin, alpha-fetoprotein (AFP), transferrin and lipoprotein were identified in c.s.f. and plasma.3. The concentrations of albumin, AFP and fetuin in c.s.f. and plasma at different gestational ages were measured using immunodiffusion and radioimmuno-assays.4. Albumin was the major protein in plasma at all ages studied (35-128 days gestation and adult). Its concentration increased throughout gestation whereas that of fetuin was similar at all fetal ages and that of AFP declined markedly during the second half of gestation. In the adult, fetuin was only about 0.1% of the total protein in plasma and AFP was not detectable.5. In 35-40 day fetuses albumin, AFP and fetuin accounted for 90% of the total protein concentration in plasma and for about 70-80% of the total protein concentration of c.s.f. As gestation progressed the concentration of all three proteins in c.s.f. declined. But the concentration of AFP and fetuin fell more rapidly and to a greater extent than that of albumin; neither AFP nor fetuin could be detected in adult c.s.f.6. The c.s.f.: Plasma ratio was above 50% for AFP and above 60% for fetuin at 35 days compared with about 25% for albumin at the same fetal age. The c.s.f.: plasma ratios for all three proteins declined with increasing fetal age and were not significantly different from each other by about mid gestation.

Albumins↗
PubMed1980

Blood-cerebrospinal fluid transfer of plasma proteins during fetal development in the sheep.

1. The penetration of human and sheep plasma proteins from blood into c.s.f. of sheep fetuses (57-86 days gestation) has been studied. The proteins were injected intravenously via cotyledonary vessels. After different time periods the c.s.f. concentrations of marker proteins were estimated by radioactive counting of iodinated human or sheep proteins or by immunoassay of human proteins.2. Several proteins of similar molecular size penetrated into c.s.f. to a different extent in 60 day fetuses. The steady-state c.s.f.: plasma ratios were about 15% for human AFP, 10% for human transferrin and sheep albumin, 7% for human alpha(1)-antitrypsin, and 5% for human albumin. In older fetuses the penetration of protein from blood into c.s.f. was much reduced and no evidence for differential penetration of different proteins was found.3. The penetration of human AFP, transferrin and sheep albumin from blood into c.s.f. was greater than can be accounted for by passive diffusion.4. The results of this paper are discussed in relation to those of the preceding paper on the identification and quantification of proteins in fetal c.s.f. and plasma. The hypothesis is put forward that the choroid plexus of the immature (60 days and less) sheep fetus contains a mechanism for the transcellular transfer of plasma proteins which may be selective in nature and of importance for some aspects of brain development.

Albumins↗
PubMed1979

Studies of the development of brain barrier systems to lipid insoluble molecules in fetal sheep.

1. The development of the blood-brain and blood-c.s.f barriers to lipid insoluble substances of different molecular radii has been studied in fetal sheep, early (60 days) and late (125 days) in gestation, using labelled erythritol (C14), sucrose (3H or 14C), inulin (3H or 14C) and albumin (125I), or albumin and IgG detected by immunoassay. 2. Morphological studies of fetal brain and choroid plexus at the same gestational stages were carried out using thin section electron microscopy and the freeze fracture techniques. 3. Penetration of markers into c.s.f. was substantially greater at 60 days than at 125 days, but at both ages the steady-state level achieved appeared to be related to molecular size. 4. A simple model describing penetration from blood into c.s.f. at 60 days is proposed. It involves the assumption that c.s.f. and brain extracellular fluid are effectively separate compartments; morphological and permeability data which supports this assumption is presented. The data for c.s.f. at 60 days are consistent with the suggestion that the markers penetrate into c.s.f. by diffusion and are not restricted by small pores in the interface between blood and c.s.f. 5. The reduction in penetration which occurred by 125 days for all markers except erythritol appears to be accounted for by an increase in the sink effect and a decrease in the effective surface area for exchange between blood and c.s.f. 6. Intercellular tight junctions of both cerebral endothelial cells and choroid plexus epithelial cells were well formed at 60 days gestation. There was no change in junctional characteristics previously thought to correlate with transepithelial permeability (tight junction depth and strand number) between the two ages studied, although there were marked changes in permeability. 7. Evidence is advanced in support of the hypothesis that in the fetus much of the penetration of lipid insoluble non-polar substances across the blood-c.s.f. barrier and perhaps across the blood-brain barrier occurs via a transcellular route consisting of a system of tubulo-cisternal endoplasmic reticulum. Penetration via the choroid plexus appears to be the dominant route for penetration from blood into c.s.f. in the 60 day fetus.

Animals↗