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Biomedical subjects

J T Turner

Publications and source records attributed to J T Turner.

At least 73 records · Page 4Linked to original sources
PubMed1990

Regulation of the neurotensin receptor and intracellular calcium mobilization in HT29 cells.

Regulation of the neurotensin receptor-inositol phosphate-intracellular Ca2+ ((Ca2+]i) pathway was studied in HT29 cells. Preincubation with neurotensin or phorbol 12-myristate, 13-acetate decreased the number of cell surface neurotensin receptors and neurotensin-induced increases of inositol trisphosphates and [Ca2+]i. The phorbol 12-myristate, 13-acetate-(43 +/- 1% at 1 microM) but not the neurotensin (65 +/- 9% at 10 nM)-induced decrease in receptors was blocked by staurosporine. The decrease in cell surface receptors was accompanied by a 55 +/- 7% shift of specifically bound 125I-neurotensin from the plasma membrane fraction to the light vesicle fraction of sucrose density gradients if a 37 degrees C incubation step was included. The time course for desensitization of [Ca2+]i mobilization was more rapid (maximal at approximately 1 min) than for loss of receptors (maximal at 45 min). After a 5-min exposure to neurotensin, the cell surface receptor number rapidly returned to control levels in the absence of agonist, but [Ca2+]i sensitivity to neurotensin recovered only partially. Incubation with carbachol, ATP or phorbol 12-myristate, 13-acetate desensitized the subsequent [Ca2+]i response to neurotensin. These results demonstrate a polyphosphoinositide-[Ca2+]i pathway in HT29 cells stimulable by neurotensin and other agents. The results from pre-incubation studies indicate that the neurotensin receptor-signaling pathway is homologously and heterologously regulated. Finally, differences in time courses for loss and recovery of cell surface receptors and desensitization of the [Ca2+]i response, as well as the lack of effect on 125I-neurotensin binding of other agonists that desensitize the neurotensin [Ca2+]i response, suggest that receptor internalization alone does not account for desensitization of the system.

Binding Sites↗
PubMed1990

Knowledge and skills for nurse administrators.

How should nurse administrators be educated for practice in today's complex environment? Mark, Turner, and Englebardt provide a thoughtful perspective on that question. The authors analyze the educational needs of two levels: the nurse executive and the nurse manager, and they look at all aspects of an effective graduate program for both career choices.

Administrative Personnel↗
PubMed1989

Regulation of Na+/K+/Cl- cotransport and [3H]bumetanide binding site density by phorbol esters in HT29 cells.

The involvement of protein kinase C in the regulation of Na+/K+/Cl- cotransport was investigated in cultured HT29 human colonic adenocarcinoma cells. We have demonstrated previously the presence of a Na+/K+/Cl- cotransport pathway in HT29 cells (Kim, H.D., Tsai, Y-S., Franklin, C.C., and Turner, J.T. (1989) Biochim. Biophys. Acta 946, 397-404). Treatment of cells with the phorbol esters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBu) caused an increase in membrane-associated protein kinase C activity that was accompanied by a concomitant decrease in cytosolic protein kinase C activity. PMA also produced a rapid transient increase in cotransport to 137% of control values by 5 min followed by a progressive decrease to 19% of control values by 2 h. To determine the underlying mechanism for the reduction in Na+/K+/Cl- cotransport, changes in cotransporter number and/or affinity were determined in radioligand binding studies using [3H]bumetanide. PMA and PDBu produced essentially identical time- and dose-dependent decreases in specific [3H]bumetanide binding that were similar to the observed decreases in cotransport. Analysis of saturation and competition binding data indicated that the decrease in binding was due to a lowered Bmax with no change in affinity. Both the decrease in binding and the changes in cotransport elicited by PMA were prevented by the protein kinase inhibitor H7. These findings suggest that phorbol esters cause a decrease in the number of cotransporters in HT29 cells, resulting in a reduction in Na+/K+/Cl- cotransport activity.

Binding, Competitive↗
PubMed1989

Opossum kidney contains a functional receptor for the Escherichia coli heat-stable enterotoxin.

The Escherichia coli heat-stable enterotoxin (ST1 or STa) binds to specific receptors on mammalian intestinal brush border membranes, and stimulates guanylate cyclase in those membranes. We have found a similar signal transduction system in brush border membranes prepared from kidney cortex of the American opossum (Didelphis virginiana, and in a cell line (OK cell) derived from that tissue. Activation of guanylate cyclase by ST1 is therefore not limited to intestinal cells. Furthermore, since it is unlikely that ST1 which is produced in the intestinal lumen, would have access to kidney receptors, this suggests the existence of an endogenous peptide resembling ST1, at least in marsupials.

Animals↗
PubMed1988

Characterization of Na+/K+/Cl- cotransport in cultured HT29 human colonic adenocarcinoma cells.

A Na+/K+/Cl- cotransport pathway has been examined in the HT29 human colonic adenocarcinoma cell line using 86Rb as the K congener. Ouabain-resistant bumetanide-sensitive (OR-BS) K+ influx in attached HT29 cells was 17.9 +/- 0.9 nmol/min per mg protein at 25 degrees C. The identity of this pathway as a Na+/K+/Cl- cotransporter has been deduced from the following findings: (a) OR-BS K+ influx ceased if the external Cl- (Cl-o) was replaced by NO3- or the external Na+ (Na+o) by choline; (b) neither OR-BS 24Na+ nor 36Cl- influx was detectable in the absence of external K+ (K+o); and (c) concomitant measurements of 86Rb+, 22Na+, and 36Cl- influx indicated that the stoichiometry of the cotransport system approached a ratio of 1N+:1K+:2Cl-. In addition, OR-BS K+ influx was exquisitely sensitive to cellular ATP levels. Depletion of the normal ATP content of 35-40 nmol/mg protein to 10-15 nmol/mg protein, a concentration at which the ouabain-sensitive K+ influx was unaffected, completely abolished K+ cotransport. OR-BS K+ influx was slightly reduced by the divalent cations Ca2+, Ba2+, Mg2+ and Mn2+. Although changes in cell volume, whether shrinking or swelling, did not influence OR-BS K+ influx, ouabain-sensitive K+ influx was activated by cell swelling. As in T84 cells, we found that the OR-BS K+ influx in HT29 cells was stimulated by exogenous cyclic AMP analogues and by augmented cyclic AMP content in response to vasoactive intestinal peptide, forskolin, norepinephrine and forskolin or prostaglandin E1.

Adenocarcinoma↗
PubMed1988

Insulin regulation of glucose metabolism in HT29 colonic adenocarcinoma cells: activation of glycolysis without augmentation of glucose transport.

The effects of insulin on glucose transport and metabolism were examined in cultured HT29 human colonic adenocarcinoma cells. The presence of glucose transporters was verified by D-glucose displaceable [3H]cytochalasin B binding. The Kd and Bmax values from cytochalasin B binding studies were 190 +/- 30 nM and 8.4 +/- 1.4 pmol/mg protein, respectively. Glucose transport determined with 3-O-methylglucose showed saturable kinetics with a Km of 5.8 +/- 0.4 mM and a Vmax of 0.047 +/- 0.003 mumol/mg protein per min at 25 degrees C. Moreover, in HT29 cells, two classes of insulin binding sites were detected in radioligand binding experiments. Although insulin failed to stimulate glucose transport, it was found to activate glycolysis in HT29 cells. Glucose consumption increased from 0.33 +/- 0.03 mumol/mg protein per h to 0.49 +/- 0.05 mumol/mg protein per h and lactate production was augmented from 0.67 +/- 0.04 mumol/mg protein per h to 0.87 +/- 0.06 mumol/mg protein per h in response to 10(-7) to 10(-5) M insulin. Insulin also enhanced mannose metabolism. Apart from these two hexoses, HT29 cells exhibited a surprisingly narrow substrate specificity. With the possible exception of glyceraldehyde, little lactate was produced from alternative substrates, including adenosine, inosine, ribose, deoxyribose, dihydroxyacetone, galactose and fructose either with or without insulin. Despite its limited utilization by the glycolytic pathway, adenosine was readily salvaged for de novo synthesis of adenine nucleotides. These findings suggest that insulin directly influences substrate utilization through the glycolytic pathway in HT29 cells without activating the glucose transport pathway.

3-O-Methylglucose↗
PubMed1988

Vasoactive intestinal peptide receptor/adenylate cyclase system: differences between agonist- and protein kinase C-mediated desensitization and further evidence for receptor internalization.

In this study we have characterized and compared the regulation of the HT29 cell vasoactive intestinal peptide receptor/adenylate cyclase system (VIP-R/AC) by the VIP-R agonist peptide histidineisoleucineamide (PHI) and by activators of protein kinase C (PKC) including phorbol 12-myristate, 13-acetate (PMA) and mezerein. Preincubation with either PHI or PKC activator decreased maximum VIP-stimulated AC activity and decreased the number of cell surface VIP-R. A [125I]VIP binding assay using solubilized VIP-R of the plasma membrane and light vesicle fractions from sucrose density step gradients was developed as a more direct measure of VIP-R internalization. Preincubation with PHI or PMA decreased plasma membrane fraction [125I]VIP binding and increased binding in the light vesicle fraction, thus providing the most direct evidence to date for translocation of VIP-R per se from the plasma membrane to another, presumably intracellular, compartment. Two experimental approaches differentiated between agonist and PKC activator regulation of VIP-R/AC. The protein kinase inhibitors H-7 and staurosporine blocked mezerein-, but not PHI-, induced losses of cell surface VIP-R. Also, down-regulation of PKC did not block PHI-induced loss of cell surface VIP-R. Thus, although both agonist and PKC activators can lead to desensitization and internalization of VIP-R, PKC is apparently not involved in the mechanisms of agonist-induced desensitization.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1988

Hostage-takers in health care settings.

No security staff is large enough to provide a safe working environment for health care personnel without the cooperation of the entire staff. Staff members must be able to recognize early in an incident when things are beginning to get out of hand so they can implement appropriate strategies to defuse the situation or call for assistance. The challenge of facing violent incidents in the health care setting will continue to grow. Hostage incidents provide the opportunity for the powerless to be heard. Incidents occur daily. No place is safe. New issues such as abortion, genetic research, and animal research along with the old issues of estrangement, insensitivity to human emotional pain, and vulnerability will ensure that violence in the medical care setting continues. Avoiding the issue will not cause it to go away and can be costly to your facility in terms of money and morale. The key to maintaining the safe environment health care workers have a right to expect lies in planning, training, and commitment. Disturbing trends in which upper level management demands that staff not document recommendations for procedures for handling violence open a pandora's box of negligence issues, not to mention professional ethics. I hope we can confront these problems in a cooperative and open manner without recrimination and fear. Failing to address them will not provide safety or long-term gain.

Health Facilities↗
PubMed1987

Alpha 2-adrenergic receptor-mediated sensitization of forskolin-stimulated cyclic AMP production.

Preincubation of HT29 human colonic adenocarcinoma cells with alpha 2-adrenergic agonists resulted in a 10- to 20-fold increase in forskolin-stimulated cyclic AMP production as compared to cells preincubated without agonist. Similar results were obtained using either a [3H]adenine prelabeling assay or a cyclic AMP radioimmunoassay to measure cyclic AMP levels. This phenomenon, which is termed sensitization, is alpha 2-adrenergic receptor-mediated and rapid in onset and reversal. Yohimbine, an alpha 2-adrenergic receptor-selective antagonist, blocked norepinephrine-induced sensitization, whereas prazosin (alpha 1-adrenergic) and sotalol (beta-adrenergic) did not. The time for half-maximal sensitization was 5 min and the half-time for reversal was 10 min. Only a 2-fold sensitization of cyclic AMP production stimulated by vasoactive intestinal peptide was observed, indicating that sensitization is relatively selective for forskolin. Sensitization reflects an increased production of cyclic AMP and not a decreased degradation of cyclic AMP, since incubation with a phosphodiesterase inhibitor and forskolin did not mimic sensitization. Increasing the levels of cyclic AMP during the preincubation (using a phosphodiesterase inhibitor) had no effect on sensitization, indicating that sensitization is not caused by decreased cyclic AMP levels during the preincubation. This rapid and dramatic sensitization of forskolin-stimulated cyclic AMP production is a previously unreported effect that can be added to the growing list of alpha 2-adrenergic responses that are not mediated by a decrease in cyclic AMP.

Adenine↗
PubMed1987

Characterization of the vasoactive intestinal peptide receptor in rat submandibular gland: radioligand binding assay in membrane preparations.

The vasoactive intestinal peptide (VIP) receptor in membranes from rat submandibular gland was studied using radioligand binding assays with 125I-VIP and various unlabeled competing ligands. In addition to the necessity of working within the parameters under which all radioligand binding assays should be performed, binding studies with 125I-VIP, as with other peptide hormones and neurotransmitters, are subject to additional technical difficulties. Specific problems that were addressed included radioligand proteolysis, the identification of an effective protease inhibitor (leupeptin) and the deleterious effects of a commonly used inhibitor (bacitracin); avid radioligand absorption to incubation tubes that was eliminated by precoating of the tubes with a combination of polyethylenimine and an organosilane; and a disproportionate effect of increasing membrane protein concentration on affinity estimates. Under optimized conditions, the affinity (Kd) and density Bmax values for 125I-VIP obtained from saturation assays (76 pM, 2.0 pmol/mg) were in excellent agreement. Membrane protein (or receptor) levels beyond the linear portion of the receptor concentration curve are often used in radioligand binding assays. Results from 125I-VIP binding studies at elevated receptor concentrations revealed the predicted marked decrease in receptor affinity. In addition, the rank order potency of unlabeled ligands in inhibition binding assays was changed. The optimization of the assay for measuring VIP receptors in submandibular gland membrane provides a reliable method for studying the role of receptor regulation in stimulus-secretion coupling for this neuropeptide.

Animals↗
PubMed1986

Disaster planning.

Explore the source record for details and available documents.

Disaster Planning↗
PubMed1985

Aggression: the healthcare protection challenge of the eighties.

Training of healthcare workers and professionals in the defusion or de-escalation of violent behavior has become essential. Healthcare facilities and staffs must assume responsibility not only for the treatment of patients but also for their safety and well-being as well as that of visitors and staff.

Health Facilities↗
PubMed1985

Writing an organizational response plan: hostage-taking incidents.

To adequately deal with a hostage-taking situation in a healthcare facility, a written response plan must be prepared and everyone in the institution who will be involved in such a situation made familiar with it. Here is an outline of what should go into such a plan.

Disaster Planning↗
PubMed1985

Alpha 2-adrenergic receptors in the human cell line, HT29. Characterization with the full agonist radioligand [3H]UK-14,304 and inhibition of adenylate cyclase.

We have characterized the alpha 2-adrenergic receptor in membranes from the human colonic adenocarcinoma cell line, HT29, using the recently introduced alpha 2-agonist 5-bromo-6-[2-imidazolin-2-yl-amino]quinoxaline [( 3H]UK-14,304), two other radioligands, and a series of adrenergic agonists and antagonists. We also investigated alpha 2-agonist inhibition of HT29 cell adenylate cyclase and reversal of inhibition by alpha-adrenergic antagonists. [3H] Yohimbine saturation experiments indicated a single class of sites with a KD of 0.61 nM which agreed with the kinetically determined KD of 0.62 nM. Computer analysis of kinetic and saturation experiments with [3H]UK-14,304 revealed two classes of sites. From the saturation data, one site had high affinity for the radioligand (0.14 nM) and comprised 33% of the total number of sites, whereas the other site had lower affinity (6.1 nM). The total number of sites labeled by [3H]UK-14,304 (360 fmol/mg of protein) was approximately equal to the number of sites labeled by [3H]yohimbine (330 fmol/mg), whereas [3H]para-aminoclonidine labeled fewer sites of a single class. Rank order potencies of adrenergic agonists and antagonists obtained from competition binding assays indicated that: the same receptors were labeled by the three radioligands, and the receptors were of the alpha 2 subtype. UK-14,304 and epinephrine inhibited forskolin- and vasoactive intestinal peptide-stimulated adenylate cyclase in a dose-dependent manner up to 32%. Inhibition of the enzyme was reversed by yohimbine and, less potently, by phentolamine and prazosin in a dose-dependent manner. The HT29 cell line appears to be a useful model system for the investigation of the regulation and mechanism of action of alpha 2-adrenergic receptors in human tissues.

Adenocarcinoma↗
PubMed1984

Alpha-2 adrenergic regulation of norepinephrine release in the rat submandibular gland as measured by HPLC-EC.

In many tissues, norepinephrine appears to inhibit its own release through an interaction at alpha adrenergic receptors. We have developed an assay for measuring the release of endogenous norepinephrine based on HPLC and have studied the regulation of release in the rat submandibular gland by alpha adrenergic antagonists. The method uses electrochemical detection to quantitate norepinephrine released from tissue slices and does not require preloading of the tissue with [3H]norepinephrine. Yohimbine, an alpha-2 adrenergic antagonist, potentiates by 50% the release caused by potassium induced depolarization with an EC50 of 0.14 microM. Prazosin, an alpha-1 antagonist, has a similar effect, but is less potent with an EC50 of 0.77 microM. Thus, the alpha adrenergic receptor mediating the regulation of norepinephrine release is of the alpha-2 subtype. The observed equal efficacies and lack of additivity of release potentiation by yohimbine and prazosin at maximal doses suggest that both drugs act at the same receptor. The five-fold difference in potency between prazosin and yohimbine is consistent with the recent observations indicating species differences between rodent and non-rodent alpha-2 adrenergic receptors.

Adrenergic alpha-Antagonists↗