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K R Peters

Publications and source records attributed to K R Peters.

At least 19 recordsLinked to original sources
PubMed1992

Freeze-substitution of chemically stabilized samples for biological field emission scanning electron microscopy.

The high resolution imaging capabilities of modern field emission scanning electron microscopes require adequately improved tissue preparation procedures to prevent the collapse of macromolecular structures and the extraction of molecules. A routine cryo-stabilization technique is described which utilizes chemical crosslinking and cryo-dehydration for mechanical and chemical stabilization of protein and lipid structures and increase of electrical conductivity of the sample. Thiocarbohydrazide (TCH) serves as a general mordant for osmium tetroxide crosslinking. However, extensive washing after all impregnation steps is necessary to dissolve unspecific osmium black precipitations at the sample surface. Collagen I aggregates showed increased stability against collapse after TCH osmification alone, whereas pulmonary surfactant liposomes require additional freeze-substitution in methanol and Freon 113 for stabilization during critical point drying. Environmental scanning electron microscopy (at water vapor pressures of 5-10 torr within the specimen chamber) was used to control, in the wet phase, the stabilization procedure at the level of chemical crosslinkage. It could be confirmed that tannic acid, often used to stabilize lipids, leads to artificial rearrangement of bilayered liposomes into compact presumable multilayered bodies, whereas the TCH osmification preserved liposome structures and their aggregates. The increase of electrical conductivity of sliced tissue was demonstrated on kidney. Support technologies for the cryo-stabilization procedures are described in detail, as well as simple routines for first stabilization trials with new samples. On pulmonary tissue, the excellent preservation of alveolar shape and fine structures of intermediate forms of surfactant are described.

Animals↗
PubMed1992

Lecture practices in United States anesthesiology residencies.

We obtained data on lecture practices from 100 of the 110 university-affiliated anesthesiology residency programs certified in the United States in 1988. Of these residency programs, 36% had a majority of their lectures before the operating room schedule began, 57% had no lectures at all in this early time slot, and 78% had morning lectures at least once a week in conjunction with a delayed operating room start. Seventy-one percent of programs had one or more afternoon lectures each week. An attendance of more than 80% was reported in 66% of the programs for morning lectures and in 50% of the programs for afternoon lectures, which is a significant difference. Aggregate pass rates on the American Board of Anesthesiology written examinations in 1987 and 1988 correlated significantly with morning-lecture attendance, but not with afternoon-lecture attendance, number of lecture days per week, or mandatory lecture attendance. These findings suggest the need for further study and definition of the role of lectures in resident education in anesthesiology.

Anesthesiology↗
PubMed1991

Persistent nidus blood flow in cerebral arteriovenous malformation after stereotactic radiosurgery: MR imaging assessment.

Stereotactic radiosurgery has become a major force in the treatment of arteriovenous malformations (AVMs) of the brain. After treatment, obliteration of flow through the malformation occurs in 75%-85% of cases within 2 years, assuming the entire AVM nidus can be encompassed by the radiation field. Because the follow-up period is relatively long, a noninvasive means to assess residual transnidus blood flow is desirable. The authors report favorable findings after a comparative analysis of 85 posttreatment magnetic resonance images and 27 follow-up cerebral arteriograms in 34 patients treated with stereotactic radiosurgery. The authors found that transnidus flow can be determined from apparent signal intensity differences between tandem two-dimensional gradient-recalled echo images obtained first without and then with gradient moment nulling (flow compensation), with empirically derived pulse parameters. This method provides a means to monitor the reduction in AVM matrix size and to assess the extent of persistent arteriovenous shunting (ie, blood flow) across the nidus.

Brain↗
PubMed1989

Alcohol use by heroin addicts: evidence for an inverse relationship. A study of methadone maintenance and drug-free treatment samples.

This study examines the relationship between the patterns of use of alcohol and heroin by narcotics addicts, and evaluates the hypothesis--frequently reported during methadone maintenance--that this form of treatment can be causally implicated in an increased consumption of alcohol. Data were obtained on lifetime patterns of alcohol and heroin use of 375 Anglo and Chicano male addicts sampled from two treatment sources: the nonmethadone (drug-free) California Civil Addict Program (CAP) and several Southern California Methadone Maintenance (MM) programs. Repeated-measures MANOVAs revealed that alcohol and heroin consumption were inversely related throughout the addicts' careers. This pattern was evident in the addiction, treatment, and postdischarge stages of Anglo and Chicano addict careers, in both the CAP and MM samples. Consequently, the authors reject the hypothesis that increased alcohol consumption is caused solely by addicts' participation in methadone maintenance treatment. Rather, the findings suggest that addicts' alcohol use during methadone treatment reflects a lifetime pattern of increased alcohol use following any decline in heroin intake.

Adult↗
PubMed1988

Outpatient pediatric neurosurgery.

In a 16-month period, 31 children underwent outpatient operations for a variety of neurosurgical problems. None of the patients experienced any anesthetic complications. One patient was admitted for management of a surgical complication and was discharged uneventfully 4 days later. A saving of at least 49.5% in hospital charges was produced when surgery was performed in the outpatient surgical facility, and a 19.8% reduction in costs was achieved when the main hospital operating suite was used on an outpatient basis. Neurosurgical procedures can be safely and inexpensively performed on an outpatient basis, even in children.

Ambulatory Care↗
PubMed1988

Attachment of plasma membranes of cultured cells to silicon chips for high magnification imaging in scanning electron microscopy.

In the membrane preparation method described in this paper, a polylysine-coated silicon chip is adsorbed to the exposed apical surface of a cell monolayer. Upon removal, the adsorbed chip separates the plasmalemma from the residual bodies of the cultured cells. This sandwich-membrane separation approach simplifies access to the cytoplasmic aspects of both the apical and the basal plasmalemma which remains on the culture substrate and is covered to a varied extent by cytoplasmic infrastructures. To stabilize the attached membranes, small crosslinking agents are used in a controlled osmium impregnation. Large crosslinkers are avoided since they induce thickening of fine structures. Optimal conditions for attachment of plasmalemma of cultured adrenal endothelial cells to the cationic chip are defined. Effective cleaning procedures of the chips and useful molecular weights of polylysine are determined by quantitating colloidal gold adherence to the surface of the chips. The specimens are examined by high resolution scanning electron microscopy.

Adrenal Cortex↗
PubMed1986

The endothelial pocket. A new structure in fenestrated endothelia.

A new endothelial cell structure, named the endothelial pocket, has been found by combined transmission and scanning electron microscopic studies of renal peritubular capillaries. Transmission EM observations made on these and other fenestrated capillaries demonstrated that each pocket consists of an attenuated fold of fenestrated endothelium that projects approximately 200 nm into the lumen above the rest of the endothelial surface. Beneath this luminal fold, there is a space and then another layer of fenestrated endothelium which abuts the basal lamina. The linear density of endothelial pockets was measured in the capillaries of the kidney cortex, intestinal mucosa and exocrine pancreas in mice and determined to be 0.067, 0.017 and 0.007 pockets X micron-1 respectively. Cationic ferritin decoration of the anionic sites on the luminal surface of the endothelium in these capillary beds revealed that both unlabelled and labelled diaphragms are clustered. In such specimens, the majority of the luminal diaphragms on endothelial pockets did not have cationic ferritin binding sites detectable by either scanning or transmission EM. On this account as well as on account of their general morphology, endothelial pockets appear to be multifold versions of the simple transendothelial channel.

Animals↗
PubMed1986

Rationale for the application of thin, continuous metal films in high magnification electron microscopy.

Various metal films of different thicknesses were deposited on to a particle test specimen and their effects on topographic contrast generation and specimen preservation were determined. Tobacco mosaic virus adsorbed on to thin carbon supports or silicon chips was imaged in TEM or high resolution SE-I SEM at a magnification of 350,000X. Tantalum films of 1-2 nm (average mass) thickness produced best contrasts and prevented volume loss of the particles from electron beam damage. Excessively thick films of 5-10 nm thickness blanketed fine structures and caused severe volume losses. Discontinuous 2 nm thick films of gold or platinum decorated the surfaces, caused a loss in topographic contrasts and induced very high volume losses. Thin continuous metal films were necessary to generate high topographic contrast and to prevent volume loss from beam damage by providing sufficient mechanical stability for small topographic features and increased thermal conductivity of the specimen surface.

Ferritins↗
PubMed1985

Endothelial plasmalemmal vesicles have a characteristic striped bipolar surface structure.

Capillary endothelial cells have a large population of small (65-80 nm diameter in transmission electron microscopy) vesicles of which a large fraction is associated with the plasmalemma of the luminal and abluminal side. We studied the fine structure and distribution of these plasmalemmal vesicles by high resolution scanning electron microscopy in cultured endothelial cells obtained from bovine adrenal cortical capillaries. Cell monolayers were covered with polylysine-coated silicon chips, split in high potassium buffer, fixed in aldehyde mixtures, and then treated with OsO4 and thiocarbohydrazide. After critical point drying, the specimens were coated with a thin (less than 2 nm) continuous film of chromium. On the cytoplasmic aspect of the dorsal plasmalemmal fragments seen in such specimens, plasmalemmal vesicles appear as uniform vesicular protrusions approximately 70-90 nm in diameter, preferentially concentrated in distinct large fields in which they occur primarily as single units. Individual plasmalemmal vesicles exhibit a striped surface fine structure which consists of ridges approximately 10 nm in diameter, separated by furrows and oriented as meridians, often ending at two poles on opposite sides of the vesicles in a plane parallel to the plasmalemma. This striped surface structure is clearly distinct from the cage structure of coated pits found, at low surface density, on the same specimens. The cytoplasmic aspect of the plasmalemma proper is covered by a fibrillar infrastructure which does not extend over plasmalemmal vesicles but on which the latter appear to be anchored by fine filaments.

Adrenal Cortex↗
PubMed1985

Working at higher magnifications in scanning electron microscopy with secondary and backscattered electrons on metal coated biological specimens and imaging macromolecular cell membrane structures.

Membrane structures of macromolecular dimensions were imaged with high resolution secondary electron type I (SE-I) signal contrasts on metal coated biological specimens. The quality of the surface information was strongly dependent on the signal used for microscopy and on the properties of metal films, i.e., thickness, continuity, structure and decoration effects. Films of 10 nm thickness produced so much type II electrons that identical images were obtained with the conventional SE-II and BSE-II signals. In such images, the type I SE signal was so low that only very weak contrasts were recognizable. If the films--continuous or discontinuous--were composed of large metal aggregates (gold and platinum) a strong micro-roughness contrast was produced by the type II signal. At high magnifications (100,000 x) this background signal greatly reduced the S/N ratio of the SE-I signal. A similar effect was previously shown to be produced by the type III background signal. The type II background signal minimized when continuous films of small aggregates (tantalum and chromium) were applied. SE-I contrast dominated in the image if the film thickness was limited to 1 nm. Additionally, it was found that gold and platinum decorated membrane surface structures, less than 20 nm in size, and did not reveal all the topographic information available (size, shape, orientation spacing of small surface features) but merely displayed center-to-center distances. These decoration effects were avoided and extensive topographic information was obtained through surface coating with Ta or Cr.

Animals↗
PubMed1984

Potassium supplementation in ritodrine-induced hypokalemia.

Acute hypokalemia occurs during infusion of beta 2 agonists for tocolysis. This study examines the efficacy of supplemental potassium in treating this hypokalemia. Four groups of dogs were anesthetized and given lactated Ringer's solution (group I), potassium chloride (group II), ritodrine hydrochloride (group III), and ritodrine plus potassium (group IV). Arterial blood gases, pH, and serum and urinary electrolytes were measured. Results were analyzed by an analysis of variance. Serum potassium fell in groups I and III, rose in group II, and remained stable in group IV. Urinary potassium levels in groups that received ritodrine (III and IV) were not different from control levels. Potassium given with ritodrine will prevent hypokalemia. However, the risks of hyperkalemia exist if vigorous replacement is undertaken. There were no dysrhythmias and no adverse effects in any of the hypokalemic animals. Therefore, the routine administration of potassium is not advocated even in obstetric patients who undergo general anesthesia.

Animals↗
PubMed1983

Fine structure of a periciliary ridge complex of frog retinal rod cells revealed by ultrahigh resolution scanning electron microscopy.

We studied the junctional region between rod inner segments (RIS) and outer segments (ROS) in frog retinas by high resolution scanning electron microscopy (SEM). Retinas of dark adapted or light exposed Rana pipiens were critical-point-dried and RIS and ROS were split and coated with ultrathin metal films of niobium and chromium--or decorated with gold--and imaged in a new SE-I imaging mode. The connecting cilium (CC) usually broke at the base of the RIS and remained attached to the ROS. The outer part of the CC plasmalemma expanded to form liplike protrusions beyond which disks evaginated with successively larger diameter until they reached the full width of the ROS. The CC rose out from an invagination of the RIS apical plasma membrane (PM). On the lateral walls of this invagination, a highly ordered complex of nine symmetrically arrayed ridges and grooves rose steeply and extended laterally approximately 0.4-1 micron on the adjacent RIS PM. On the apical plasmalemma, the ridges and grooves formed groups of three to four parallel rows that surrounded the invagination. The grooves were bridged by filaments anchored at the top edges of the ridges. This highly ordered structure we term the periciliary ridge complex (PRC). Its ninefold symmetry apparently reflects the 9 + 0 microtubule organization of the CC axoneme. The three-dimensional structure revealed by SEM was confirmed by transmission electron microscopy (TEM) of sections of Epon-embedded retinas. TEM-immunocytochemistry on thin sections of retinas embedded in glutaraldehyde cross-linked albumin suggested that the PRC and the CC may participate in opsin transport and disk morphogenesis.

Animals↗
PubMed1982

Conditions required for high quality high magnification images in secondary electron-I scanning electron microscopy.

High quality of secondary electron (SE) images, taken at useful magnifications of 100,000 to 200,000, require new signal generation and collection methods and new metal coating procedures. High quality is defined as the condition under which image contrast describes accurately the topographic features of the specimen in a size range that approximates the beam diameter. Such high resolution contrasts are produced by the SE (SE-I) generated by a small electron probe on the specimen surface. Tobacco mosiac virus and ferritin molecules deposited on bulk substrates were introduced as test specimens to check the image quality obtained. The SE-I signal contrast could be imaged when SE (SE-III), produced by backscattered electrons (BSE) at the pole piece of the final lens, were eliminated with an electron absorption device attached to the pole piece. This signal collection procedure will be referred to as "Secondary Electron-I Image" (SE-I image) mode. In addition to the SE-III, BSE generate SE-II in the specimen itself. On specimens deposited on bulk gold or platinum, and coated with the same metals SE-II produced a microroughness contrast that limited particle resolution in the SE-I image mode to approximately 10 nm. Reduction of SE-II and enrichment of the signal in SE-I was achieved by using continuous fine crystalline coatings of tantalum, niobium and chromium. By applying these metals in films of approximately 2.0 nm thickness, the SE-I contrast generation was found to be indepedent of the atomic number of the metal. Edge sharpness was improved when the specimens were coated with low atomic number metals. Under these conditions, the quality of images obtained in SE-I image mode equals that of images obtained in TEM from identically coated specimens and was limited only by the size of the topographic details, beam diameter and beam current.

Ferritins↗
PubMed1981

Application of a general equation for controlled pore glass permeation chromatography to an aggregating. Spherical virus.

A semi-empirical permeation chromatography equation relating pore size, species size and elution coefficient, which had previously been derived from chromatographic data of narrow-molecular-weight dextrans on controlled pore glass, was applied to the chromatography of an aggregating virus particle. A large number of chromatographic runs on columns of different pore sizes were combined and statistically evaluated. The resulting diameter distribution versus infectivity curve for the virus particle population shows distinct maxima at multiples of 50 nm. This unit size agrees with electron microscopical observations and confirms the applicability of the chromatography equation.

Chromatography↗