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Biomedical subjects

S J Morris

Publications and source records attributed to S J Morris.

At least 19 recordsLinked to original sources
PubMed1992

Polyunsaturated fatty acid incorporation into plasmalogens in plasma membrane of glioma cells is preceded temporally by acylation in microsomes.

Plasmalogens (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) are major phospholipids in many tissues and cells, particularly of neural origin. Using cultured C6 glioma cells and subcellular fractions isolated on Percoll gradients we investigated selectivity for esterification of several polyunsaturated fatty acids (PUFA) in the sn-2 position of plasmalogens compared to [1-14C]hexadecanol, representative of de novo synthesis of the ether-linked sn-1 position. In whole cells at a final concentration of 105 microM PUFA, 2-4 nmol plasmalogen/mg protein was labeled in 4 h and 10-14 nmol in 24 h, representing 8-15% and 35-50%, respectively, of initial plasmalogen mass. Incorporation of label from hexadecanol was lower than PUFA incorporation (20:5(n-3) greater than 20:4(n-6) greater than 18:3(n-3) much greater than 18:2(n-6)) suggesting deacylation-reacylation at the sn-2 position. Plasmalogens accounted for 50% of total cell ethanolamine phospholipids and 75% in plasma membrane. Using a novel, improved method for extraction of subcellular fractions containing Percoll, plasma membrane also was enriched in plasmalogen relative to microsomes (107.4 +/- 5.2 vs. 40.0 +/- 2.9 nmol/mg protein). Selectivity for esterification at the sn-2 position of plasmalogens with respect to chain length and unsaturation of the fatty acyl chain was similar in both subcellular fractions and reflected that of whole cells. Labeling of plasma membrane with PUFA and fatty alcohol lagged behind that of microsomes. Chase experiments in cells prelabeled with [1-14C]18:3(n-3) for 2 h showed no significant reduction of label in plasmalogen of any subcellular fraction although accumulation of label in the microsomal fraction was slowed initially. Reduction of plasmalogen label (40-50%) did occur in microsomes and plasma membrane when cells prelabeled for 24 h were switched to chase medium with or without chase fatty acid. Our data suggest that esterification of PUFA to plasmalogen may occur at the endoplasmic reticulum with subsequent translocation to plasma membrane resulting in accumulation of relatively stable pools of plasmalogen that are not readily accessible for deacylation-reacylation exchange with newly appearing PUFA. Alternatively, deacylation-reacylation may occur in a more stable phospholipid pool within the plasma membrane but would involve a slower process than at the endoplasmic reticulum.

Acylation↗
PubMed1992

A multidisciplinary educational program to promote head and neck cancer screening.

An educational program to promote screening through primary health care for the squamous cell cancers of the buccal cavity, pharynx, and larynx as developed and implemented, and its impact on screening was documented. Providers of care for high-risk patients at seven inner-city health care sites in Boston were identified and targeted for training. Of the 327 providers who were targeted for training from December 1986 through June 1989, 261 (80%) attended educational sessions. Screening exams were documented on an average of 14.7 patients per targeted provider through December 1989. The educational program was associated with a large increase in documented screening for these cancers, compared with baseline rates. Several adaptations in the program were required, including a demonstration of efficient screening to address the concerns of these providers about time constraints. Variations in the quantity and quality of documented screening among health care sites were noted.

Boston↗
PubMed1979

Kinetics of cation-induced aggregation of Torpedo electric organ synaptic vesicles.

Synaptic vesicles from the Torpedo ray can be induced to aggregate in the presence of Ca2+ and K+ in the 4 mM and 50 mM range, respectively. The reactions are strikingly similar to those of chromaffin granule membranes reported previously (Morris, S.J., Chiu, V.C.K. and Haynes, D.H. (1979) Membrane Biochem. 2, 163-202). The Ca2+-induced reaction includes dimerization and higher order aggregation, and is shown to be due to electrostatic screening interactions and bindng to negatively-charged groups on the membrane surface. The K+-induced reaction includes only dimerization and is shown to be due to screening interactions alone. The kinetics of the dimerization reactions were studied using the stopped-flow rapid mixing technique. The Ca2+-induced reaction has a 'bimolecular' rate constant of 4.77 . 10(8) M-1 . s-1. These values are close to the limit of diffusion control (8.03 . 10(9) M-1 . s-1), indicating that no large energy barriers or structural barriers to aggregation exist. Arrhenius plots for the Ca2+-induced aggregation showed a break at 5 degrees C. Above this temperature, the activation energy is low (+0.65 kcal/mol), consistent with the above. Below this temperature, the activation energy is high, consistent with a membrane structure change increasing theenergetic and structural barriers. This information, and the observation of a high stability constant of the complex, were taken as evidence for the involvement of 'recognition sites' on the membrane surface. The results were analyzed in terms of an encounter complex model in which vesicles with separations of 26-126 A are considered capable of transformation into a stable complex. The rate constant of the transformation step is 1.4 . 10(3) s-1 for Ca2+ and approx. 1.6 . 10(5) s-1 for K+. The values are compared with previous results for chromaffin granule membranes and for phospholipid vesicles derived from chromaffin granule lipids and from acidic phospholipids. The half-time for Ca2+-induced transformation of the encounter complex into the stable complex is 435 microseconds. It is concluded that the recognition sites are almost as optimally deployed as the vesicle plasma membrane recognition sites involved in exocytotic release.

Animals↗
PubMed1979

Light scattering turbidity changes as a measure of the kinetics of Ca2+ -promoted aggregation of chromaffin granule membrane ghosts.

Changes in turbidity seen when chromaffin granule membrane ghosts are aggregated by Ca2+ can be modelled as dimerization of hollow spheres using Rayleigh-Gans-Debye light-scattering theory. The experimental changes agree well with the calculations. Thus, if shape or refractive index changes produced by osmotic perturbation, ion uptake, etc. can be excluded, turbidity readings can be used to follow the progress of the aggregation reaction of storage vesicles and other small particles or macromolecules.

Animals↗
PubMed1979

The lipid and protein content of cholinergic synaptic vesicles from the electric organ of Torpedo marmorata purified to constant composition: implications for vesicle structure.

The lipid, protein, acetylcholine and ATP content of cholinergic synaptic vesicles isolated from the richly innervated electric organ of Torpedo marmorata and purified to constant composition has been determined. The number of vesicles present in the preparations has been estimated by quantitative electron microscopy and the mean composition of the vesicle deduced. The acetylcholine content of the purest preparations was considerably greater than that previously attained and reached a mean of 6.10 mmole/g of protein and 2.6 X 10(5) molecules/vesicle; the mean values, for all determinations, were 4.1 +/- S.E.M. 0.6 and 2.6 X 10(5) +/- S.E.M. 0.6 X 10(5) respectively. The lipid and protein content of the vesicle (about 140 and 80 ag/vesicle respectively) is relatively low, indicating a thin, lipid-rich membrane and a highly hydrated core of which not more than 1-2% can be occupied by protein. These findings are consistent with conclusions drawn from recent density determinations made at different osmotic pressures using penetrating and non-penetrating gradients.

Acetylcholine↗
PubMed1979

Diarrhea after gastrectomy and vagotomy.

Development of diarrhea in a patient following gastric surgery can be a confusing problem. The clinician is forced to consider and exclude causes that may be independent of the surgery as well as those that are unique to the postgastrectomy state. An orderly approach is mandatory for appropriate workup and management.

Biopsy↗
PubMed1979

Divalent cation-induced aggregation of chromaffin granule membranes.

Divalent cations induce the aggregation of chromaffin granule ghosts (CG membranes) at millimolar concentrations. Monovalent cations produce the same effect at 100-fold higher concentrations. The kinetics of the dimerization phase were followed by light-scattering changes observed in stopped-flow rapid mixing experiments. The rate constant for Ca2+-induced dimerization (kapp) is 0.86-1.0 x 10(9) M-1sec-1, based on the "molar" vesicle concentration. This value is close to the values predicted by theory for the case of diffusion-controlled reaction (7.02 x 10(9) M-1sec-1), indicating that there is no energy barrier to dimerization. Arrhenius plots between 10 degrees and 42 degrees C support this; the activation energy observed, +4.4 Kcal, is close to the value (4.6-4.8 Kcal) predicted for diffusion control according to theory. Artificial vesicles prepared from CG lipids were also found to have cation-induced aggregation, but the rates (values of kapp) were less than 1/100 as large as those with native CG membranes. Also, significant differences were found with respect to cation specificity. It is concluded that the slow rates are due to the low probability that the segments of membrane which approach will be matched in polar head group composition and disposition. Thus large numbers of approaches are necessary before matched segments come into aposition. The salient features of the chromaffin granule membrane aggregation mechanism are as follows: (a) In the absence of cations capable of shielding and binding, the membranes are held apart by electrostatic repulsion of their negatively charged surfaces. (b) The divalent and monovalent cation effects on aggregation are due to their ability to shield these charges, allowing a closer approach of the membrane surfaces. (c) The major determinants of the aggregation rates of CG membranes are proteins which protrude from the (phospholipid) surface of the membrane and serve as points of primary contact. Transmembrane contact between these proteins does not require full neutralization of the surface charge and surface potential arising from the negatively charged phospholipids. (d) After contact between proteins is established, the interaction between membranes can be strengthened through transmembrane hydrogen bonding of phosphatidyl ethanolamine polar head groups, divalent cation-mediated salt bridging, and segregation of phosphatidylcholine out of the region of contact.

Adrenal Medulla↗
PubMed1979

Brucella-induced cholecystitis.

Acute cholecystitis is a rare complication of systemic brucellosis. This report details the occurrence of acute noncalculous cholecystitis in which Brucella suis was cultured from both the blood and the gallbladder. A discussion of the various diagnostic tests and the recommended therapy for brucellosis is included.

Acute Disease↗
PubMed1979

Radiation therapy of a pancreatic fistula.

A patient with a pancreatic cutaneous fistula subsequent to laparotomy was unresponsive to medical management including intravenous hyperalimentation. Radiation therapy resulted in progressive diminution of volume from the fistula with subsequent complete closure. Radiation thus offers another therapeutic modality for pancreatic fistulas.

Female↗
PubMed1978

Jaundice, choledocholithiasis, and a nondilated common duct.

In two cases of jaundice due to choledocholithiasis, the biliary tree was not dilated on skinny-needle transhepatic cholangiography. Visualization of the biliary tree before arriving at a diagnosis in certain cases of jaundice is needed.

Cholangiography↗
PubMed1978

A structural model of cholinergic synaptic vesicles from the electric organ of Torpedo marmorata deduced from density measurements at different osmotic pressures.

Density measurements made on cholinergic synaptic vesicles from the electric organs of Torpedo marmorata at different osmotic pressures are consistent with the following structural model of the vesicle. The particle behaves like a sphere 80-100 nm in diameter bounded by a semi-permeable membrane. The bulk of its soluble constituents are in true solution at physiological osmolalities. The limiting membrane is approximately 4-5 nm thick, suggesting that it contains large areas of phospholipid bilayer exposed to its bathing medium. The limiting membrane takes up about 26% (v/v) of the particle, a further 34% (v/v) of which is osmotically active water and 31% (v/v) hydrated core material at 800 mosmol/1. The buoyant density of the membrane is 1.132 g . cm-3. The density of the hydrated core material is approximately 1.05 g . cm-3. The membrane is selectively permeable to small molecules when subjected to hypo-osmotic stress. It is proposed that this occurs by the formation of small transient pores in the lipid bilayer of the membrane, which are induced by stretching caused by the osmotic pressure change.

Acetylcholine↗