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D R Scott

Publications and source records attributed to D R Scott.

At least 55 records · Page 3Linked to original sources
PubMed1993

The site of acid secretion in the mammalian parietal cell.

Initiation of acid secretion in the gastric mucosa is accompanied by a morphological transformation in which the acid pump, the H+/K(+)-ATPase, translocates from a cytoplasmic vesicular location to the secretory surface lining the canaliculi. Associated with the morphological changes, activation of K+ and Cl- pathways are necessary to supply K+ to the extracytoplasmic face of the pump. Although the pump in the secretory membrane is known to secrete acid, it is not known whether activation of the KCl pathway occurs in the tubulovesicular membrane prior to the formation of the canaliculus, or when the pump is in the secretory membrane. The cellular site of activation of acid secretion in the rabbit gastric parietal cell was investigated using the covalent binding of [3H]omeprazole as a probe of acid secretion in rabbit gastric glands that were undergoing stimulation in vitro. This compound depends on an acidic environment for activation and covalent binding to the H+/K(+)-ATPase. Electron microscopic autoradiography showed that activation of the enzyme occurred only when it was present in the canalicular membrane and not when it was present in the cytoplasmic tubulovesicular membrane. Hence there is likely to be a physical separation of K+ and/or Cl- pathways from the ATPase in the resting cell, and stimulation of acid secretion is dependent on colocalization of these pathways in the canalicular membrane.

Aminopyrine↗
PubMed1993

Histamine secretion from rat enterochromaffinlike cells.

BACKGROUND: In vivo studies have suggested an important role for gastric enterochromaffinlike (ECL) cells in mediating acid secretion. Direct evidence for this function is lacking and requires a preparation of highly purified ECL cells. This work investigates the possible role and mechanism of histamine release from the ECL cell in the peripheral regulation of acid secretion, using purified ECL cells from rat fundic mucosa. METHODS: A combination of elutriation and density-gradient centrifugation was used to purify rat fundic ECL cells. Enrichment was determined by the presence of acidic vacuoles containing a V type adenosine triphosphatase, electron microscopy, immunostaining, and histamine content and release. RESULTS: ECL cells were enriched at least 65-fold with respect to the fundic epithelium. Gastrin (EC50 0.2 nmol/L) and cholecystokinin octapeptide (nonsulfated, EC50 0.04 nmol/L) stimulated histamine release in a time- and dose-dependent manner, suggesting a CCK-B receptor subtype, confirmed by the inhibition of gastrin/CCK stimulation with the CCK-B antagonist L365,260. Somatostatin also inhibited gastrin-mediated histamine release. Single cell imaging showed that gastrin elevated intracellular cytosolic calcium concentration biphasically. Carbachol and the C kinase activator 120-tetradecanoylphorbol-13-acetate also stimulated histamine release. Epinephrine (blocked by propranolol), forskolin, and dibutyryl-5'-cyclic adenosine monophosphate were also effective, implicating a beta-adrenergic pathway. The H3 agonist R-alpha-methyl-histamine inhibited, whereas the H3-antagonist thioperamide potentiated gastrin/CCK stimulated histamine release. CONCLUSIONS: These in vitro results support a central role for the ECL cell in the peripheral regulation of gastric acid secretion.

Animals↗
PubMed1993

Solution structure of the V3 loop of a Thailand HIV isolate.

The principal neutralizing determinant (PND) of human immunodeficiency virus (HIV) is located inside the third variable loop (designated the V3 loop) of the envelope glycoprotein gp120. The V3 loop is typically 35 amino-acids long, and the 1st and the 35th residues in the loop are invariant cystines involved in a disulfide-bridge. Although PNDs from different HIV isolates contain a conserved GPG-sequence, the amino acids flanking the conserved sequence show hypervariability among HIV isolates; the GPG and the two flanking regions are collectively referred to as the GPG-crest or the PND. The amino acid sequence variability in the GPG-crest gives rise to different antigenic specificities for different PNDs from different HIV isolates. By combining two-dimensional nuclear magnetic resonance (2D NMR) and molecular modeling techniques, we have developed a method to study (1) the global tertiary fold of the V3 loops of HIV and (2) the local structure of the PND at the tip of the V3 loop. In this article, we report the results of our structural studies on the V3 loop of a Thailand HIV isolate. The sequential assignment is made by combining DQF-COSY, TOCSY, and NOESY/ROESY experiments. Various intra- and inter-residue inter-proton distances are estimated by full-matrix analyses of the NOESY data at 100 and 400 ms of mixing times and of the ROESY data at 60 and 200 ms of mixing times. 100 inter-residue distances are used as structural constraints in a simulated annealing procedure to derive energetically stable structures. Two functional motifs in the V3 loop, i.e., the glycosylation site and the GPG-crest, form defined structures: a turn is located at the glycosylation site, and the GPG-crest forms a protruding domain with a type-II GPGQ turn. The other regions of the V3 loop are rather flexible--especially the C-terminal DIRKAYC-stretch. These flexible regions of the V3 loop lead to conformational flexure of the entire V3 loop without altering the local structures of the glycosylation site or the GPG-crest. However, the ROESY experiments revealed no slow exchange among different V3 loop conformations, and therefore the flexible conformations are in fast exchange within the NMR time scale. The extent of this conformational flexibility is also discussed.

Amino Acid Sequence↗
PubMed1992

Determination of the sidedness of the C-terminal region of the gastric H,K-ATPase alpha subunit.

It cannot be predicted from hydropathy analysis whether the C-terminal end of the alpha subunit of the gastric H,K-ATPase is cytoplasmic or extracytoplasmic. The sideness of the C-terminal amino acids was determined by taking advantage of the two C-terminal tyrosines in the primary sequence of the enzyme. Intact, cytoplasmic side out vesicles derived from hog gastric mucosa or detergent solubilized vesicles were iodinated by the lactoperoxidase method and then the C-terminal amino acids hydrolyzed by carboxypeptidase Y. The alpha and beta subunits were separated by SDS gel electrophoresis. The level of iodination of the alpha subunit following solubilization was about three fold greater than when intact vesicles were iodinated, and the beta subunit was iodinated only when solubilized enzyme was used. Carboxypeptidase Y removed 28 +/- 4% of the radioactivity from the alpha subunit iodinated in intact vesicles. These data are consistent with a cytoplasmic location of the C-terminal amino acids of the alpha subunit and with a mostly extracytoplasmic location of the amino acids of the beta subunit.

Animals↗
PubMed1992

Effects of cold on vascular permeability and edema formation in the isolated cat limb.

We investigated the effects of cold temperatures on microvascular protein permeability in the isolated constant-flow perfused cat hindlimb. The perfusates were 20% cat plasma-80% albumin-electrolyte solution (low-viscosity perfusate, approximately 1 cP) or whole blood (high-viscosity perfusate, approximately 4 cP). The time at low temperature (less than 10 degrees C) was less than 3 h (short term) or greater than 5 h (long term). Decreases in the solvent drag reflection coefficient (sigma f) indicated increases in permeability. The sigma f's were determined with the integral-mass balance method from measurement of changes in protein concentration and hematocrit induced by fluid filtration into the tissues. Short-term cold exposure did not increase permeability with either a low- or a high-viscosity perfusate, whereas long-term exposure with limb temperatures of approximately 5 degrees C significantly increased permeability when the perfusate was whole blood. In addition, we verified our previous prediction that flow had to be reduced to 6-8 ml.min-1.100 g-1 to avoid the hydrostatic edema caused by short-term perfusion with whole blood at approximately 5 degrees C. Also, we found that at approximately 3 degrees C histamine's permeability-increasing effect was totally abolished, whereas at approximately 20 degrees C this effect was partially inhibited. Hence, constant-flow perfusion at low temperature with whole blood can cause edema by a pressure-dependent mechanism, whereas long-term perfusion with this perfusate at low temperatures can cause a permeability increase that further compounds edema formation. Histamine is not responsible for this permeability increase.

Animals↗
PubMed1991

Muscarinic responses of gastric parietal cells.

Isolated rabbit gastric glands were used to study the nature of the muscarinic cholinergic responses of parietal cells. Carbachol (CCh, 100 microM) stimulation of acid secretion, as measured by the accumulation of aminopyrine, was inhibited by the M1 antagonist, pirenzepine, with an IC50 of 13 microM; by the M2 antagonist, 11,2-(diethylamino)methyl-1 piperidinyl acetyl-5,11-dihydro-6H-pyrido 2,3-b 1,4 benzodiazepin-6-one (AF-DX 116), with an IC50 of 110 microM; and by the M1/M3 antagonist, diphenyl-acetoxy-4-methylpiperidinemethiodide (4-DAMP), with an IC50 of 35 nM. The three antagonists displayed equivalent IC50 values for the inhibition of carbachol-stimulated production of 14CO2 from radiolabeled glucose, which is a measure of the turnover of the H,K-ATPase, the final step of acid secretion. Intracellular calcium levels were measured in gastric glands loaded with FURA 2. Carbachol was shown to both release calcium from an intracellular pool and to promote calcium entry across the plasma membrane. The calcium entry was inhibitable by 20 microM La3+. The relative potency of the three muscarinic antagonists for inhibition of calcium entry was essentially the same as for inhibition of acid secretion or pump related glucose oxidation. Image analysis of the glands showed the effects of carbachol, and of the antagonists, on intracellular calcium were occurring largely in the parietal cell. The rise in cell calcium due to release of calcium from intracellular stores was inhibited by 4-DAMP with an IC50 of 1.7 nM, suggesting that the release pathway was regulated by a low affinity M3 muscarinic receptor or state; Ca entry and acid secretion are regulated by a high affinity M3 muscarinic receptor or state, inhibited by higher 4-DAMP concentrations (greater than 30 nM), suggesting that it is the steady-state elevation of Ca that is related to parietal cell function rather than the [Ca]i transient. Displacement of 3H N-methyl scopolamine (NMS) binding to purified parietal cells by CCh showed the presence of two affinities for CCh, but only a single affinity for 4-DAMP and lower affinity for pirenzepine and AFDX 116, providing further evidence for the parietal cell location of the [Ca]i response. Elevation of steady-state [Ca]i levels with either ionomycin or arachidonic acid did not replicate M3 stimulation of acid secretion or glucose oxidation, hence elevation of [Ca]i is necessary but not sufficient for acid secretion.

Aminopyrine↗
PubMed1991

Microvascular permeability transients due to histamine in cat limb.

We measured the protein solvent drag reflection coefficient (sigma f) and the capillary filtration coefficient (CFC) before and after adding 1 or 10 microM histamine to the recirculating fluid (20% plasma, remainder albumin and electrolytes, hematocrit of 1-2%) perfusing the isolated cat hindlimb preparation. Transient sigma f measurements were made at 3- to 15-min intervals after histamine using a modification of the steady-state integral-mass balance method. CFC measurements were made at approximately 10-min intervals after histamine in separate experiments. A 1 microM dose of histamine caused sigma f to fall from approximately 0.8 to approximately 0.3 in 2-3 min; sigma f then returned to control in approximately 20 min. CFC response to the 1 microM histamine was a peak increase approximately 2 times control and a return to control in approximately 40 min. A 10 microM dose caused sigma f to fall rapidly to near zero. In general, recovery was much slower than for the 1 microM dose, most of the limbs not returning to control by 40 min after histamine. CFC measurements after 10 microM histamine increased only approximately 5 times control even though sigma f was near zero at the same time. CFC remained above control for approximately 60 min. The combined sigma f and CFC data could be described quantitatively if histamine simultaneously opened both short-lived large gaps (approximately 1,000 A) and a longer-lived pathway that sieved protein like the normal pathway and if the numbers of channels of each pathway closed exponentially with 4- and 15-min time constants, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Second messengers in the gastric gland: a focus on calcium.

The rabbit gastric gland model was used to study the nature of the muscarinic cholinergic and gastrin responses of parietal cells. Carbachol (100 microM) stimulation of acid secretion, as measured by the accumulation of aminopyrine, was inhibited by the M1 antagonist pirenzepine with an IC50 of 13 microM; by the M2 antagonist 11,2-(diethylamino)methyl-1-piperidinyl acetyl-5,11-dihydro-6H-pyrido 2,3-b 1,4-benzodiazepin-6-one (AF-DX 116) with an IC50 of 110 microM; and by the M3 antagonist diphenylacetoxy-4-methylpiperidinemethiodide (4-DAMP) with an IC50 of 35nM. The three antagonists displayed similar IC50 values for the inhibition of carbachol-stimulated production of 14CO2 from radiolabeled glucose, which is a measure of the turnover of the H(+)-H(+)-ATPase. Intracellular calcium levels wer measured in gastric glands loaded with FURA2. Carbachol was shown both to release calcium from an intracellular pool and to promote calcium entry across the plasma membrane. The calcium entry was inhibitable by 20 microM La3+. The relative potency of the three muscarinic antagonists for inhibition of calcium entry was essentially the same as for inhibition of acid secretion or metabolism. However, the rise in cell calcium due to release of calcium from intracellular stores was inhibited by 4-DAMP with an IC50 of 1.7 nM. Image analysis confirmed that the effect of carbachol and of the antagonists on intracellular calcium was occurring in the partial cell. In particular, the high-affinity inhibition of calcium release by 4-DAMP occurs in the parietal cell. Accordingly, it appears that the secretory receptor of the parietal cell is of the M3 type, and acid secretion depends on the entry of calcium rather than on calcium release from intracellular stores. In parallel experiments gastrin (G-17-sulfated) produced a dose-dependent increase in intracellular calcium (EC50, 0.14 +/- 0.013 microM). No stimulation of acid secretion was observed, but pepsinogen secretion was stimulated dose-dependently (EC50 = 1.17 +/- 0.21 microM).

Acetylcholine↗
PubMed1990

Implantation of scleral-fixated posterior chamber intraocular lenses.

A surgical technique for implanting a posterior chamber intraocular lens (IOL) in eyes without capsular or zonular support is presented. A 10-0 polypropylene suture attached to a standard needle is tied to the apex of each haptic and passed transclerally through the ciliary sulcus to secure the haptics at the 3 o'clock and 9 o'clock meridians. This technique produced good visual results in six aphakic patients who were contact lens intolerant, two patients in whom capsular or zonular rupture at the time of cataract surgery precluded standard nonsuture fixation techniques, one patient who had intracapsular cataract extraction for a subluxated, cataractous lens, and one patient who had secondary IOL implantation in combination with penetrating keratoplasty for aphakic bullous keratopathy. Advantages over other techniques of posterior chamber lens implantation in the absence of capsular support include technical ease, avoidance of iris fixation, and more precise placement of scleral fixation sutures, thus minimizing IOL decentration.

Adult↗
PubMed1989

Congenital idiopathic corneal endotheliopathy.

Two unrelated boys had a history of bilateral corneal clouding at birth following uncomplicated full-term gestations and spontaneous vaginal deliveries (without forceps). Clinical examinations disclosed bilateral corneal edema, no inflammation, and normal intraocular pressures. There was no history of similarly affected family members. The patients underwent penetrating keratoplasty at ages 4 months (patient 1) and 12 years (patient 2). Light and electron microscopic studies of the corneal buttons from both patients revealed areas of degeneration of the endothelium and separation of rounded endothelial cells. The morphologic features were strikingly similar to those in two acquired forms of corneal disorders--autoimmune endotheliopathy and "acute endotheliitis." Immunocytologic and in situ hybridization studies for herpes simplex virus were not consistent with either productive or latent corneal infection. Ultrastructural changes in Descemet's membrane reflect delayed or abnormal development of the postnatal nonbanded layer in patients 1 and 2, respectively. These suggest an intrauterine insult that resulted in endothelial dysfunction. The histologic and ultrastructural features of these two congenital cases are not typical of those seen in any of the recognized causes of congenital corneal clouding. We propose that these cases represent a unique congenital corneal endotheliopathy of undetermined origin.

Child↗
PubMed1989

Angiographic embolization of intractable puerperal hematomas.

Puerperal hematomas may not respond to conventional therapy, including vaginal packing, drainage, and hypogastric artery ligation. Two cases are presented in which selective angiographic arterial embolization was used to manage this potentially lethal complication.

Angiography↗
PubMed1988

South African health care and the proprietary medicine industry.

A large-scale national sample survey was conducted to assess the health and sickness profiles of the population by conventional demographic parameters. The objective was to ascertain how people treated particular ailments and in particular how and when they used proprietary medicines and other self-medication alternatives rather than a professional medical practitioner. The attitudes to self-medication by the respondents were largely positive. Self-selected treatments were perceived to be successful. A panel of physicians was asked to comment on the medical suitability of the ailments chosen for self-treatment and of the medicines selected. People were deemed generally to administer self-medication responsibly and sensibly and in the case of more serious ailments did, correctly, consult professionals.

Adolescent↗
PubMed1988

Medical management of a high bleb phase after trabeculectomies.

In the first 2 months after trabeculectomy, elevated intraocular pressure (IOP) associated with a high bleb develops in some patients. This has been referred to as an encysted bleb, and some have recommended surgical techniques to repair it and to restore controlled IOP. This clinical picture occurred in 18 of 181 eyes (10%) undergoing simple trabeculectomy with a limbus-based conjunctival flap and tenonectomy. It did not occur among 69 eyes in which trabeculectomy with a fornix-based flap was combined with extracapsular cataract extraction (ECCE). Its occurrence may, therefore, be related to surgical technique. In eyes with this syndrome, the authors used IOP-lowering eyedrops and/or pills, along with continued corticosteroid eyedrops. None required surgical manipulation. All 18 eyes achieved long-term IOP control, and in 14 all medications were ultimately discontinued. An hypothesis is suggested to explain the occurrence of this event and the rationale for this therapy. A trial of IOP-lowering treatment is indicated in the management of a high bleb phase after filtering surgery.

Adolescent↗
PubMed1987

Savings from generic drug substitution in the RSA--is its cost justified?

The causes of the recent rapid increases in health care costs in the RSA are briefly studied. Drug costs have increased largely through the use of new innovations, greater usage and price factors, but price increases have been below the rate of inflation. The savings in drug costs to be expected from the introduction of generic substitution have been calculated to be low in relation to overall health care costs, although of significance in relation to the survival of individual drug manufacturing businesses. The thrust towards generic substitution is possibly misplaced in that the potential savings in hospitalisation costs from the discovery of new drugs are so large that they justify the encouragement of the innovative drug manufacturers.

Cost Control↗
PubMed1987

Integral-mass balance method for determination of solvent drag reflection coefficient.

We have developed the integral-mass balance (IMB) method to measure the solvent drag reflection coefficient (sigma f) for transcapillary macromolecular transport in skeletal muscle and other organs. Of course, sigma f is calculated from the cumulative amounts of water and macromolecule that move convectively across the microvascular membrane as determined from changes in hematocrit and plasma macromolecule concentration over a period of fluid filtration. We have investigated the effects of both theoretical and experimental factors that affect the validity and accuracy of the method. The effect of the following factors on sigma f determination by the IMB method were explored: low Peclet number; random-measurement errors; and systematic errors due to vascular leakage, hemolysis of red blood cells, evaporation, and osmolality changes. We found that all of these factors produced overestimations of sigma f, but their effects could be corrected. Also, appropriate experimental design could minimize these effects. Experiments using the IMB method in the isolated, perfused cat hindlimb preparation to determine sigma f for albumin and plasma proteins resulted in mean values of 0.82 +/- 0.08 (SD) (n = 7) and 0.83 +/- 0.02 (n = 4), respectively.

Animals↗
PubMed1985

Motor axon sprouting in frog sartorius muscles is not altered by contralateral axotomy.

Sartorius muscles of the frog Rana pipiens were used to study the incidence of motor nerve sprouting in normal unoperated muscles, in experimental muscles contralateral to axotomy of the sartorius nerve, and in sham-operated control muscles. Muscles were stained with either a combination of nitroblue tetrazolium nerve terminal stain and cholinesterase stain or with a combination of silver nerve terminal stain and cholinesterase stain. Each endplate that could be clearly seen was classified into one or more of the following categories: normal endplates without sprouts, three types of terminal sprouts, preterminal sprouts, nodal sprouts, sprouts of unknown origin and destination, and doubly innervated gutters. A quantitative study of 318 endplates from nine unoperated muscles, 779 endplates from 45 experimental muscles, and 694 endplates from 41 control muscles showed that all muscles had a high incidence of motor nerve sprouting and other forms of remodelling (20-28% of all endplates). There were, however, no significant differences between experimental, control, and unoperated muscles when results obtained with the same stains were compared. Results obtained with the two different stains were only slightly different. We conclude that sprouting is a very common but highly variable feature of normal frog neuromuscular junctions, and in the sartorius, contralateral axotomy does not alter this ongoing remodelling.

Animals↗
PubMed1984

Anoxia and capillary filtration coefficient in the isolated cat hindlimb.

Isolated cat hindlimbs were perfused from a reservoir with an albumin-blood mixture at a constant flow of 20 ml X min-1 X 100 g muscle-1 while alternately bubbling the perfusate with either 95% O2-5% CO2 gas mixture or a 95% N2-5% CO2 mixture for 50- to 60-min periods. Capillary filtration coefficient (CFC), vascular resistance (R), and perfusate O2 content were measured in each period. The arterial O2 content fell from fully equilibrated to 0.25 vol% during the use of N2. R fell from about 6 mmHg X min X 100 g X ml-1 during O2 bubbling to approximately 1.0 with N2. CFC averaged 0.012 +/- 0.002 ml X min-1 X mmHg-1 X 100 g muscle-1 (SD, n = 6) during the 1st O2 period, rising to 0.016 +/- 0.002 (n = 4) in the 3rd O2 period 4 h later. CFC fell by 5% (P less than 0.001) during the periods of N2 bubbling. Papaverine was present in two experiments without effect on the CFC data. It was concluded that CFC was not meaningfully influenced by vascular resistance or anoxia, a finding that is inconsistent with the concept of local metabolic control of CFC by precapillary resistance vessels.

Animals↗