Biomedical subjects

J A Williams

Publications and source records attributed to J A Williams.

At least 19 recordsLinked to original sources

PubMed1992

Effects of calyculin A on amylase release in streptolysin-O permeabilized acinar cells.

The effects of the phosphatase inhibitors calyculin A and okadaic acid on amylase release from streptolysin-O permeabilized rat pancreatic acini were investigated. Both agents induced similar biphasic effects with moderate potentiation of calcium-stimulated amylase release at medium and strong inhibition at higher concentrations. Calyculin A was thirty times more potent than okadaic acid and at 100 nM totally inhibited calcium-induced amylase release while 3 microM okadaic acid reduced amylase release by 78%. 100nM calyculin A also completely inhibited GTP gamma S-potentiated amylase release and partially inhibited phorbol ester potentiated secretion. The data indicate that inhibition of a serine/threonine phosphatase, probably a type 1 phosphatase, leads to inhibition of calcium-induced amylase release in permeabilized pancreatic acini.

Amylases↗

PubMed1992

Endothelin increases [Ca2+]i in rat pancreatic acinar cells by intracellular release but fails to increase amylase secretion.

In individual fura-2 loaded cells of rat pancreatic acini endothelin-1 (ET-1) (10-50 nM) induced sustained oscillations in [Ca2+]i. At higher concentrations a larger, but transient increase in [Ca2+]i was observed, which was largely unaffected by removal of extracellular Ca2+. ET-1 induced the release of Ca2+i from the same store as cholecystokinin (CCK), but with less potency. At concentrations of endothelin which transiently increased Ca2+, ET-1 increased the accumulation of inositol phosphates. Specific binding sites for 125I-endothelin were demonstrated on rat pancreatic acini. A single class of binding sites was identified with an apparent Kd 108 +/- 12 pM and Bmax of 171 +/- 17 fmol/mg for ET-1. The relative potency order for displacing [125I]ET was ET-1 greater than ET-2 greater than ET-3. In contrast to CCK and the non-phorbol ester tumour promoter Thapsigargin (TG) which induce both transient and sustained components of [Ca2+]i elevation, ET-1 failed to increase amylase release over the range 100 pM-1 microM.

Amylases↗

PubMed1992

U73122 inhibits Ca2+ oscillations in response to cholecystokinin and carbachol but not to JMV-180 in rat pancreatic acinar cells.

Stimulation of rat pancreatic acinar cells with low concentrations of phosphatidylinositol (PI)-linked secretagogues induces [Ca2+]i oscillations, without measurable changes in the formation of inositol 1,4,5-trisphosphate. Therefore, we tested U73122 a new phospholipase C inhibitor to determine if PI turnover is necessary for the generation of [Ca2+]i oscillations. In acini prelabeled with [3H]inositol, PI hydrolysis on stimulation with either cholecystokinin or carbachol was inhibited dose-dependently by U73122, with a maximal effect seen at 10 microM; the formation of inositol 1,4,5-trisphosphate, measured using a radioreceptor assay, was also similarly inhibited. By contrast secretin- or vasoactive intestinal peptide-stimulated production of cAMP was unaffected by 10 microM U73122. These studies indicate that U73122 is a relatively specific inhibitor of G-protein-mediated phospholipase C activation in pancreatic acini. In fura-2-loaded acini, U73122 inhibited the increases in [Ca2+]i stimulated by these high concentrations of secretagogues which can be demonstrated to elicit PI turnover. The [Ca2+]i signal generated by directly stimulating G-proteins with sodium fluoride was also inhibited by U73122; however, the [Ca2+]i rise induced by thapsigargin was unaffected. These data indicate that the mechanism of inhibition was distal to the occupation of cell surface receptors but did not involve an interference of Ca2+ metabolism in general. When [Ca2+]i oscillations were elicited by low concentrations of cholecystokinin or carbachol, U73122 rapidly inhibited the oscillating [Ca2+]i signal. In contrast, oscillations induced by an analogue of cholecystokinin, JMV-180, which does not stimulate changes in PI metabolism at any concentration, were unaffected. This indicates that cholecystokinin- and carbachol-induced oscillations are probably initiated by small, localized changes in PI metabolism, which are not readily detectable. However, the inability of U73122 to inhibit JMV-180-induced oscillations indicates that PI metabolism may not necessarily be a prerequisite for the generation of [Ca2+]i oscillations.

Animals↗

PubMed1992

The comparative strengths of commercial glass-ionomer cements with and without metal additions.

Metal reinforced glass-ionomer cements are said to possess superior mechanical properties when compared to non-metal reinforced glass-ionomer cements. However, the literature to date does not always support this view, owing to the variety of materials and test methods employed. In this study the mechanical properties of three reinforced and three standard materials were tested using the standard specification tests of compressive and diametral strength in addition to tensile strength using the four point bend test. The tensile strength was also measured using the shell test in order that this test, which on theoretical grounds is more suited to these materials, may be evaluated. Six specimens of each material were prepared for each of the test modalities resulting in the conclusion that the addition of metal to glass-ionomer cements can markedly increase the strength of the materials. However, the method of fusing the metal to the glass rather than by simple addition does not produce any advantages in strength. In this evaluation one reinforced material was significantly stronger than all other materials in all four test modalities. The compressive strength test which appears in most standards does not appear to be very discriminatory. Of the tensile tests, which have more clinical significance, the results of the diametral strength tests, which are included in some standards, appear to be at variance with the other two tensile tests, suggesting that the flexural or shell test would be more appropriate.

Cermet Cements↗

PubMed1992

Transforaminal escape of a lumbar epidural catheter.

A patient is presented whose lumbar epidural catheter was found to lie in the paravertebral tissues during a right radical nephrectomy. The catheter had been placed with the patient awake and the procedure performed in a routine fashion without difficulty or indication of catheter malposition. Four ml of 2% CO2 lidocaine were initially injected as a test dose without any demonstrable effect. After the induction of general anaesthesia, fentanyl 100 mu and 0.25% bupivacaine 10 ml were injected slowly into the catheter. Previous studies suggest that transforaminal escape of an epidural catheter occurs after 1-6% of insertions. It may occur without nerve root symptoms during catheter placement. The authors recommend that epidural catheters be introduced whilst the patients are awake and an effective block demonstrated before induction of general anaesthesia.

Aged↗

PubMed1992

In vitro erosion of 20 commercial glass ionomer cements measured using the lactic acid jet test.

The lactic acid jet test has been proposed for incorporation in international standards for dental cements, since results correlate well with in vivo erosion. In the literature, jet test results have been reported on only six glass ionomer cements. This study examines three types of glass ionomer, restorative, luting and metal reinforced, twenty materials from six manufacturers. A wide range of erosion rates was found particularly for restorative cements. The hypotheses put forward by previous workers to explain differences in erosion rates found on their limited range of glass ionomers do not apply to the wider range that we tested.

Biocompatible Materials↗

PubMed1992

Quantitative comparison of radiolabeled antibody therapy and external beam radiotherapy in the treatment of human glioma xenografts.

Using 90Yttrium radiolabeled antibodies, radioimmunotherapy was compared to fractionated external beam radiotherapy in the treatment of human glioma xenografts. Antibody treatments required administration of an approximately threefold greater total dose compared to external beam treatments to achieve the same tumor regrowth delay. Following multi-fraction external beam radiation treatments, tumor regrowth delay demonstrated a large fractionation effect (alpha/beta = 2.3 Gy, 95% confidence limits 0.4-4.2 Gy), suggesting that much of the ineffectiveness of the antibody treatments could be caused by a large dose-rate effect in this system. Despite the large fractionation effect, the regrowth delay was small for a large single-fraction external beam irradiation, possibly because of tumor hypoxia. When compared to external beam radiation, radiolabeled antibody treatments resulted in a comparatively diminished tumor bed effect, suggesting radioimmunotherapy spares normal tissue surrounding the tumor.

Animals↗

PubMed1992

Identification of a novel 5-HTN (Nematoda) receptor from Ascaris suum muscle.

1. The abilities of various serotonergic drugs to bind with the 5-HT receptor of Ascaris suum muscle and to affect cyclic AMP levels in muscle tissue were examined. 2. Ligands which selectively interact with either the 5-HT1 or the 5-HT2 receptor in mammalian systems interact with the 5-HT receptor from A. suum muscle and increase cyclic AMP levels. 3. No binding of 5-HT3 ligands to 5-HT receptors from A. suum muscle was observed. 4. The 5-HT receptor of A. suum muscle should be called the 5-HTN (for Nematoda) receptor because its pharmacological and biochemical behaviors were different from those of mammalian 5-HT receptors.

Animals↗

PubMed1992

The treatment of pelvic soft tissue radiation necrosis with hyperbaric oxygen.

OBJECTIVE: The purpose of this study was to examine the therapeutic effects of hyperbaric oxygen on radiation-induced soft tissue necrosis in patients who previously received treatment for a gynecologic malignancy. STUDY DESIGN: Fourteen patients whose necrotic wounds failed to heal after 3 months of conservative therapy were enrolled in a prospective observational study. Outcome of hyperbaric oxygen treatment was measured by resolution of necrosis. RESULTS: Fourteen patients underwent 15 courses of hyperbaric oxygen treatments. All those with radiation necrosis of the vagina alone or in association with rectovaginal fistula had complete resolution of necrosis with hyperbaric oxygen. Only one treatment failure occurred. CONCLUSION: Hyperbaric oxygen is a safe, effective, and well-tolerated treatment for radiation-induced soft tissue necrosis.

Adult↗

PubMed1992

A P element chimera containing captured genomic sequences was recovered at the vestigial locus in Drosophila following targeted transposition.

A P element carrying the Dopa decarboxylase gene, P[Ddc], was targeted into vg21, a cryptic P element induced mutant allele of the vestigial (vg) locus. The resulting allele, vg28w, contained the expected P[Ddc] plus an additional 9.5 kb of DNA, captured from elsewhere on chromosome II. Reversion of the vg28w mutant allele demonstrated that the entire insert can excise but cannot reinsert at an appreciable frequency. We explain the targeted transposition as the repair of a double stranded gap, created by the excision of the P element at vg21, and suggest that the formation of chimeric elements may be an important component of P element dependent genomic instability.

Alleles↗

PubMed1992

Regulation of phospholipid hydrolysis in streptolysin-O-permeabilized rat pancreatic acini.

To investigate the mechanism of phospholipid hydrolysis in pancreatic acinar cells, the effects of Ca2+, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) and cholecystokinin (CCK) on both polyphosphoinositide (PI) and phosphatidylcholine (PC) hydrolysis were studied in rat pancreatic acini permeabilized with the bacterial toxin, streptolysin-O. When acini were prelabeled with myo-[3H]inositol, permeabilized, and then incubated with various concentrations of free Ca2+ for 15 min, Ca2+ stimulated [3H]inositol phosphate release at a concentration of 100 nM and was maximally effective at 100 microM. Both GTP gamma S and CCK enhanced Ca(2+)-induced [3H]inositol phosphate release, although these agents had no effect in the absence of Ca2+. At a physiological concentration of Ca2+ (100 nM), CCK stimulated [3H]inositol phosphate release which was further enhanced by GTP gamma S. When acini were similarly prelabeled with [3H]choline before permeabilization, [3H]choline phosphate release was also stimulated by free Ca2+ over the concentration range from 100 nM to 10 microM. In contrast to PI hydrolysis, however, neither GTP gamma S, CCK, or GTP gamma S plus CCK had an additional effect on [3H]choline phosphate release stimulated by 100 nM-100 microM free Ca2+. Furthermore, Ca(2+)-induced [3H]choline phosphate release appeared to be due to the redistribution from cell to the medium rather than to an increase in choline phosphate production. Therefore, choline phosphate release following prelabeling with [3H]choline is not useful as an indicator of PC hydrolysis in permeabilized acini.

Animals↗

PubMed1992

The pancreatic duct cell.

A conference entitled "The Pancreatic Duct Cell: Physiology and Pathophysiology" was held September 26-29, 1991, at the Engineering Society Club of Baltimore. The conference was organized by a committee consisting of John Williams of the University of Michigan (Co-Chair), Daniel Longnecker of Dartmouth Medical School (Co-Chair), Barry Agent of Newcastle Upon Tyne, Raymond Frizzell of the University of Alabama at Birmingham, Sherwood Githens of the University of New Orleans, and Sarah Kalser of the NIDDK. The meeting was sponsored by the NIDDK with contributions from NCI, NIDR, ADAMHA, and the American Gastroenterological Association. About 100 investigators from the United States, England, Canada, Germany, Norway, and Israel attended the conference. The participants were based in a number of distinct disciplines including both basic and clinical sciences. While the main focus was on pancreatic ducts, comparison of salivary and bile ducts was also included.

Animals↗

PubMed1992

Prolonged hepatic ischaemia due to liver injury: a case report.

A case is reported in which a young male who underwent right hepatectomy necessitated by gunshot wound to the liver, survived 2 h 20 min of normothermic hepatic ischaemia. This case extends the documented duration of hepatic ischaemia compatible with survival and documents the histopathology of the post-ischaemic liver.

Adult↗

PubMed1992

Low molecular mass GTP-binding proteins in subcellular fractions of the pancreas: regulated phosphoryl G proteins.

Low molecular mass guanine nucleotide-binding proteins [small guanosine 5'-triphosphate (GTP)-binding proteins] and phosphoproteins of the pancreatic acinar cell were compared by two-dimensional gel electrophoresis. [35S]GTP alpha S blotting analysis of the total cell protein revealed 20 GTP-binding proteins ranging in molecular mass from 20 to 28 kDa and pI of 4.8-6.4. Analysis of 32P-labeled total cell protein revealed over 300 phosphoproteins. The subcellular distribution of the small GTP-binding proteins was examined: 17 were located in the rough endoplasmic reticulum (RER) fraction, 19 in the smooth microsome fraction, 14 in the zymogen granule membrane fraction, and 11 in the cytosolic fraction, with overlap between fractions. Of the GTP-binding proteins, two were also found to be phosphoproteins, one located on the RER and one on the zymogen granule membrane. The phosphorylation of both small GTP-binding proteins was increased by secretagogue stimulation of the cells but with different time courses. The RER small GTP-binding protein demonstrated a rapid and transient increase in 32P labeling, whereas the granule membrane small GTP-binding protein showed an increase at longer times (30 min). Two of the cytosolic small GTP-binding proteins were also seen in particulate fractions, especially in the zymogen granule membrane fraction, suggesting the possibility of cycling between cytosolic and membrane-associated forms.

Animals↗

PubMed1992

Effects of okadaic acid indicate a role for dephosphorylation in pancreatic stimulus-secretion coupling.

Okadaic acid completely inhibits phosphatase 2A at nanomolar concentrations, while complete inhibition of type 1 phosphatases occurs at 1 microM. Phosphatase 2B is significantly inhibited only at concentrations > 1 microM. In rat pancreatic acini, 1 microM okadaic acid shifted the cholecystokinin (CCK) dose-response curve for stimulating amylase release to the right without reducing maximal secretion. At 3 microM, okadaic acid inhibited maximal CCK-induced amylase release to 78 +/- 7% of control, whereas the inactive analogue 1-Nor-okadaone had no effect. Three lines of evidence indicate that this inhibition by okadaic acid occurs at a late step in stimulus-secretion coupling: 1) intracellular Ca2+ signaling in response to agonist stimulation was not appreciably altered by okadaic acid; 2) stimulation with phorbol ester plus thapsigargin (thus by-passing receptor activation), which gave 85 +/- 4% of maximal CCK-induced amylase release, was inhibited 66 +/- 4% by 3 microM okadaic acid; and 3) Ca(2+)-induced amylase secretion in streptolysin O-permeabilized cells was also reduced by 85 +/- 7%. Two-dimensional polyacrylamide gel electrophoresis of 32P-labeled acini and autoradiography demonstrated that okadaic acid dose dependently increased overall protein phosphorylation. Correspondingly, okadaic acid also led to an inhibition of CCK-induced dephosphorylation. These results show that okadaic acid inhibits pancreatic acinar secretion at a step after generation of intracellular messengers and indicate a role for protein dephosphorylation in stimulus-secretion coupling.

Amylases↗

PubMed1992

Regulation of [Ca2+]i by secretagogue stimulation of canine gastric parietal cells.

The ability of gastrin, histamine, and carbachol to stimulate acid secretion by direct action on gastric parietal cells is well established but the role of intracellular Ca2+ concentration ([Ca2+]i) in mediating these effects is the subject of some controversy. To examine this issue further, secretagogue-mediated changes in [Ca2+]i in single isolated canine gastric parietal cells were examined by microspectrofluorometry of fura-2-loaded cells. Resting [Ca2+]i in single parietal cells was 63 +/- 6 (SE) nM. Carbachol, 10(-5) M, induced a maximum elevation in [Ca2+]i with an initial transient rise of 178 +/- 24 (SE) nM, which was maintained in the absence of extracellular Ca2+ and a sustained plateau of 112 +/- 20 (SE) nM, which was abolished by removal of extracellular Ca2+. Both effects were reversed by the muscarinic receptor antagonist atropine. Gastrin (10(-9)-10(-7) M) also induced a bimodal rise in [Ca2+]i with a maximal initial transient rise of 206 +/- 14 nM and a sustained plateau of 94 +/- 9 nM. Both components of the [Ca2+]i response to gastrin were reversed by the gastrin specific antagonist L 365260. Lower concentrations of gastrin (10(-10) M) induced repetitive transient increases (oscillations) in cytosolic Ca2+. The amplitude of the first spike was less than 50% of the transient rise in [Ca2+]i stimulated by 10(-8) M gastrin. The oscillations occurred at a rate of 0.9/min, gradually decreasing in amplitude within 15 min of secretagogue administration. Histamine (10(-4) M) led to a minimal rise in [Ca2+]i (less than 5% of control) in less than 10% of the canine parietal cells tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

ATP induces two cholecystokinin binding affinity states in permeabilized rat pancreatic acini.

The influence of adenine and guanine nucleotides on cholecystokinin (CCK) receptor binding was examined in streptolysin O-permeabilized rat pancreatic acini. Specific binding of tracer to intact acini was 12.1 +/- 0.4% per milligram protein, while permeabilized acini bound 34.6 +/- 2.9% (n = 7). The increase in binding was also seen when normalized to DNA. Binding to permeabilized acini was reduced by the presence of 1 mM ATP to 23.0 +/- 1.3%. Analysis of competitive inhibition of tracer binding by unlabeled CCK-8 was consistent with binding to two affinity states on intact acini, with the equilibrium dissociation constants for the high (KdH)- and low (KdL)-affinity states equal to 41 +/- 5 pM and 5.2 +/- 0.4 nM, respectively; permeabilized acini displayed a single binding site with Kd = 598 +/- 40 pM. In the presence of 1 mM ATP, two states were seen on permeabilized acini with KdH = 85 +/- 11 pM and KdL = 2.7 +/- 0.6 nM. ATP, ATP gamma S, GTP, and GTP gamma S all inhibited binding, with half-maximal inhibition occurring at greater than 1 mM, 21 microM, 5 microM, and 0.4 microM, respectively. GTP gamma S (1 microM) also induced two affinity states with KdH = 112 +/- 7 pM and KdL = 1.5 +/- 0.2 nM (n = 3). Binding of CCK to pancreatic membranes was also decreased by ATP, and a similar regeneration of two binding affinity states was observed. ATP also decreased binding of [125I-Tyr4]bombesin to permeabilized acini, but in contrast did not generate two measurable binding affinity states.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗

PubMed1992

Membrane properties of mesopontine cholinergic neurons studied with the whole-cell patch-clamp technique: implications for behavioral state control.

1. The whole-cell patch-clamp technique was used to study the membrane properties of identified cholinergic and noncholinergic laterodorsal tegmental neurons in slices of rat brain maintained in vitro. 2. On the basis of their expression of the transient outward potassium current IA and the transient inward calcium current IT, three classes of neurons were observed: type I neurons exhibited a large IT; type II neurons exhibited a prominent IA; and type III neurons exhibited both IA and IT. 3. Combining intracellular deposition of biocytin with NADPH diaphorase histochemistry revealed that the vast majority of type III neurons were cholinergic, whereas only a minority of type I and type II neurons were cholinergic. Thus mesopontine cholinergic neurons possess intrinsic ionic currents capable of inducing burst firing. 4. Delineation of the intrinsic membrane properties of identified mesopontine cholinergic neurons, in concert with recent results regarding the responses of these neurons to neurotransmitter agents, has led us to present a unifying and mechanistic hypothesis of brain stem cholinergic function in the control of behavioral states.

4-Aminopyridine↗