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S L Howell

Publications and source records attributed to S L Howell.

144 records · Page 8Linked to original sources
PubMed1969

Isolation and properties of secretory granules from rat islets of Langerhans. I. Isolation of a secretory granule fraction.

A method has been devised for the isolation of a secretory granule fraction from isolated rat islets of Langerhans. The islets were homogenized in buffered sucrose, and the homogenate was separated into nuclear, mitochondrial, secretory granule, and microsomal fractions by differential centrifugation. The secretory granule fraction was purified by differential centrifugation in discontinuous sucrose density gradients. A greater degree of purification could be achieved by the use of two successive gradients of this type, although the final yield was greatly reduced. Biochemical and morphological characterization of the fractions was obtained; the secretory granule fraction contained both insulin and glucagon. The limiting membranes of the granules remained intact and the general appearance of the granules was similar to that seen within the whole islet cells.

Animals↗
PubMed1969

Isolation and properties of secretory granules from rat islets of Langerhans. II. Ultrastructure of the beta granule.

Beta granules isolated from rat islets of Langerhans and subjected only to phosphotungstic acid had, in negatively stained images, a 50-A periodicity. This periodicity was also observed in thin-section profiles of beta granules in intact cells. In shadowed preparations, the granules were spherical in shape and had irregular edges and surface structure. The presence of such a periodicity in the beta granule indicates that its matrix may be composed of a crystalline material.

Animals↗
PubMed1969

Isolation and properties of secretory granules from rat islets of Langerhans. 3. Studies of the stability of the isolated beta granules.

A partially purified secretory granule fraction, isolated from rat islets of Langerhans by differential centrifugation, was used for investigating the stability of the beta granules during incubation in various conditions. Effects of pH, temperature, and time were studied; the granules possessed optimal stability at 4 degrees and pH 6.0, and could be solubilized at pH 4.0 or 8.5, or in the presence of sodium deoxycholate, but not by phospholipase c, ouabain, or alloxan. Incubation with glucose or some of its metabolites, or with tolbutamide, ATP, or cyclic 3',5'-AMP did not alter the stability of the beta granules Exogenous insulin-(131)I was not bound by the isolated granules under the conditions used; no specific insulin-degrading activity could be detected in subcellular fractions of the islets. These findings indicate that intracellular solubilization of the granules with subsequent diffusion of the insulin into the extracellular space is not a likely mode of insulin secretion in vivo, and suggest that a crystalline zinc-insulin complex may exist in the matrix of the beta granules.

Animals↗
PubMed1969

Beta granule formation in isolated islets of langerhans: a study by electron microscopic radioautography.

The distribution of radioautographic grains over organelles within the beta cells of rat islets of Langerhans was investigated at various times after pulse labeling of the isolated islets with tritium-labeled amino acids. Ten minutes after the start of labeling most of the grains were situated over the endoplasmic reticulum and cytoplasm; by contrast, 60 min from the start of labeling the majority of the grains were associated with the beta granules. At 20, 30, and 45 minutes after pulse labeling the proportion of grains associated with the Golgi complex was increased two- to three-fold over the 10- or 60-minute values. The distribution of radioautographic grains over granules in the intact cells did not suggest that the electron-lucent type of secretory granules were precursors of the electron-opaque granules. Furthermore, studies of the pattern of grains over granules isolated by centrifugation 60 min after pulse labeling showed no preferential labeling of the electron-lucent type of granule. It is concluded that labeled amino acids are incorporated initially in the endoplasmic reticulum, and that the label subsequently appears in the beta granules. The Golgi complex participates either in the formation of the beta granule or in the translocation of the granule through the cytoplasm of the cell.

Animals↗
PubMed1968

Potassium ions and the secretion of insulin by islets of Langerhans incubated in vitro.

1. A method was devised for the isolation of islets of Langerhans from rabbit pancreas by collagenase digestion in order to study the influx and efflux of K(+) in islets during insulin secretion. 2. Glucose-induced insulin release was accompanied by an increased rate of uptake of (42)K(+) by the islets of Langerhans, though this was not the case for secretion in response to tolbutamide. Ouabain significantly inhibited the uptake of (42)K(+) by islet tissue. 3. No significant increase in the rate of efflux of (42)K(+) was demonstrated during active insulin secretion. 4. Slices of rabbit pancreas were incubated in media of different K(+) content, and rates of insulin release were determined. Alteration of the K(+) concentration of the medium between 3 and 8mm had no effect on the rate of insulin release by pancreas slices. However, decrease of the K(+) concentration to 1mm resulted in inhibition of secretion in response to both glucose and to tolbutamide. Conversely, an increase in K(+) concentration increased rates of insulin release in response to both these stimuli. 5. It is concluded that, though unphysiological concentrations of K(+) may influence the secretion of insulin, fluxes of K(+) in the islets do not appear to be important in the initiation of insulin secretion.

Animals↗
PubMed1967

The secretion of newly synthesized insulin in vitro.

1. An immunological method for the purification of small quantities of insulin has been devised. 2. This method has been used to isolate labelled insulin secreted from pancreas slices incubated in vitro. The insulin had previously been labelled by incubation of the slices with [(3)H]leucine in vitro. 3. There is some release of labelled insulin when such slices are further incubated in media of low glucose content. When the glucose content of the medium is raised, little additional radioactive insulin is released in the first hour after labelling. However, there is a marked increase in specific radioactivity of insulin released from slices in response to a high concentration of glucose in the second and third hours. Release of labelled insulin is again diminished in the final phase, 4hr. from the start of the experiment. 4. These results are discussed in relation to possible mechanisms of insulin release from the beta-cell.

Journal Article↗
PubMedDate not supplied

Utilizing narrative inquiry to evaluate a nursing doctorate program professional residency.

Because the University of Colorado (CU) School of Nursing Nursing Doctorate (ND) Program initiated an innovative nursing educational reform, emerging program evaluation challenges were addressed to ensure successful implementation and program quality. The study's purpose was to evaluate the effectiveness of the ND professional clinical residency (fourth and final year) from the students' perspectives. Therefore, this evaluation was exploratory and inductive to focus on the primary questions: "How does one become an ND nurse during the residency?" (process) and "What is an ND nurse?" (outcome). Additionally, an explanation of how interactive processes affected residency experiences was addressed. The narrative inquiry framework made available a special access to the human experiences of time, order, and change during the residency process. Ten students in the first CU ND Program residency participated. Narrative data for qualitative analysis were obtained from students' monthly written vignettes and verbal sharing of their clinical experiences during conferences. Vignette formats directed students to describe significant residency experiences and share reflections on the events. One finding suggested that students' formative progression through the residency occurred in four phases similar to cognitive development theories. Additional findings confirmed students' growth toward and summative attainment of ND outcome behaviors, including holistic clinical proficiency, client advocacy, and promotion of professional growth for colleagues.

Adult↗
PubMedDate not supplied

An example of cocaine tolerance in a gunshot wound fatality.

A 29-year-old male received a fatal gunshot wound to the head during an altercation. Routine toxicological followup on the victim revealed a concentration of 30 mg/L of cocaine in the blood. The case history presented suggests that the concentration achieved by this individual was the result of a physiological tolerance developed from years of consistent recreational use and not by an intentional or accidental overdose.

Adult↗