Biomedical subjects

J C Kermode

Publications and source records attributed to J C Kermode.

34 records · Page 2Linked to original sources

PubMed1987

Nature and functioning of the pertussis toxin-sensitive G protein of neutrophils.

A specific, pertussis toxin-sensitive, GTP binding, regulatory protein of neutrophils which we term "Gn" couples the reaction of chemotactic factors with their specific receptors to the resultant stimulation of chemotaxis, granule enzyme secretion, O2- generation, aggregation etc. The ability of four chemotactic formylpeptides to increase the GTPase activity of isolated plasma membranes of rabbit neutrophils correlates almost perfectly with the ability of the same peptides to cause granule enzyme release. These and other findings provide formal evidence for the previous assumption that fMET-Leu-Phe increases the GTPase activity of Gn by reacting with the same receptor that triggers granule enzyme release and other stimulated functions of the neutrophil. The molecular weight of 40 kDa and isoelectric point of 5.5 of the [32P] ADP-ribosylated alpha subunit of Gn, differ slightly but significantly from the corresponding alpha subunits of the other G proteins that are substrates for pertussis toxin. Differences also exist in the patterns of proteolytic fragments of the alpha subunit of Gn and those of the other G proteins. These observations indicate that in neutrophils a G protein distinct from the previously identified pertussis toxin substrates couples the stimulation of chemotactic receptors to the physiological function of cells. The dissociation constants of binding (Kd) for the high and low affinity sites of the formylpeptide receptor of rabbit peritoneal neutrophils and the ability to induce secretion of beta glucosaminidase from the same cells were determined for each of seven chemotactic formylpeptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Heterogeneity of binding of chemotactic formyl peptides to their receptors on rabbit neutrophils: methodological and analytical considerations in the study of complex receptor-binding patterns.

The pattern of binding of chemotactic formyl peptides to their receptors on intact rabbit neutrophils was investigated using three different radiolabeled formyl peptides. The purpose of the study was both to establish suitable procedures for the analysis of complex receptor-binding data and to evaluate the heterogeneity of binding of the chemotactic formyl peptides. Radiolabeled formylmethionyl-leucyl-phenylalanine was found to require repurification by thin-layer chromatography before it was of sufficient purity for use in these studies. All three radioligands were essentially stable during the binding assay. The 'LIGAND' computer program proved suitable for a detailed and rigorous analysis of the binding data. Each of the three formyl peptides showed significant heterogeneity in its binding pattern and all appeared to interact with the same receptor sites. The degree of heterogeneity, however, was greater with formylnorleucyl-leucyl-phenylalanine than with the other two formyl peptides. The heterogeneity was close to the theoretical limit of discernibility; thus individual binding studies with one formyl peptide did not always show statistical evidence of the heterogeneity. The study also highlighted the severe uncertainty in estimates of the proportions of each type of binding site when such data are analyzed on the basis of the 'two binding site' model.

Animals↗

PubMed1986

Pertussis toxin as a probe of neutrophil activation.

In reviewing our own and other work, it is clear that pertussis toxin treatment of neutrophils causes a time- and concentration-dependent inhibition of granule enzyme secretion induced by formylmethionylleucylphenylalanine (fMet-Leu-Phe), C5a, leukotriene (LT) B4 and platelet-activating factor (PAF). Chemotaxis, O2- generation, aggregation, and arachidonic acid production induced by fMet-Leu-Phe are also inhibited by pertussis toxin. Granule enzyme release caused by A23187 or phorbol 12-myristate 13-acetate is not inhibited. The inhibition of neutrophil function correlates closely with the NAD-ribosylation of a 41,000-dalton protein in the neutrophil plasma membrane, presumably the GTP-binding regulatory protein Ni. Pertussis toxin treatment prevents or obtunds the increased influx of Ca2+ induced by fMet-Leu-phe and LTB4, but not that caused by stimulation of neutrophils with PAF. Pertussis toxin prevents the receptor-induced breakdown of polyphosphoinositides in intact neutrophils and isolated membrane and prevents or decreases the production of inositol 1,4,5-trisphosphate (IP3) and 1,2-diacylglycerol. The hypothesis advanced by us and others is that pertussis toxin interacts with a GTP-binding regulatory protein identical or similar to Ni, which couples receptor-chemotactic factor interaction to phospholipase C activation. Inhibition of the activation prevents the production of IP3 and the resulting release of Ca2+ from intracellular stores and of 1,2-diacylglycerol and thus, the activation of protein kinase C. The lack of these two mediators is the immediate cause of the depression of neutrophil activation resulting from pertussis toxin. Some of the limitations and uncertainties of our present knowledge with respect to this hypothesis are discussed.

Animals↗

PubMed1985

Thyrotrophin receptors, tumour radioiodine concentration and thyroglobulin secretion in differentiated thyroid cancers.

Tumour radioiodine concentration has been compared with serum thyroglobulin (Tg) and, in a few cases, with tumour complement of thyrotrophin receptors in patients with differentiated thyroid carcinoma. All tumours examined possessed TSH receptors. In most the complement was similar to that of normal thyroid tissue although all but one of the tumours had no detectable 131I concentration in vivo even with excess TSH stimulation. Elevated serum Tg (patient taking T4 in suppressive dose) was generally associated with tumours which had 131I concentrating function when stimulated by excess TSH. Some patients, however, had high serum Tg concentration but only low or indetectable tumour 131I uptake. We conclude that (a) measurement of tumour TSH receptor complement is unlikely to be useful in clinical management as tumours which do not significantly concentrate 131I in vivo may have a normal TSH receptor complement and (b) the capacity to secrete Tg is usually associated with 131I concentration but quantitatively the relationship varies considerably between tumours.

Adult↗

PubMed1985

The inhibition of neutrophil granule enzyme secretion and chemotaxis by pertussis toxin.

Pertussis toxin treatment of rabbit peritoneal neutrophils causes a concentration-dependent inhibition of granule enzyme secretion induced by formylmethionyl-leucyl-phenylalanine, C5a, and leukotriene B4. It also inhibits chemotaxis induced by formylmethionyl-leucyl-phenylalanine. The same toxin treatment, however, has no effect on granule enzyme secretion induced by the calcium ionophore A23187 or phorbol 12-myristate 13-acetate. Moreover, pertussis toxin treatment does not affect either the number or affinity of the formylpeptide receptors on the neutrophil nor does it have any effect on the unstimulated levels of cyclic AMP (cAMP) or the transient rise in cAMP induced by chemotactic factor stimulation in these cells. We hypothesize that pertussis toxin, as in other cells, interacts with a GTP binding regulatory protein identical with or analogous to either Ni or transducin which mediates the receptor-induced inhibition or activation of a target protein or proteins required in neutrophil activation. The nature of the target protein is unknown, but it is not the catalytic unit of adenylate cyclase. The target protein acts after binding of chemotactic factor to its receptor in the sequence that leads to the receptor-induced rise in intracellular Ca2+. It does not affect the responses elicited by the direct introduction of calcium into the cells or the activity of protein kinase C.

Adenylate Cyclase Toxin↗

PubMed1984

Receptors for thyroid-stimulating hormone in normal and pathological human thyroid tissues.

The receptors for TSH have been studied in human thyroid tissue to assess their density and binding characteristics in various disease states. A single set of similar independent receptors appeared to be present in both healthy and pathological thyroid tissue. Their binding affinity for bovine TSH averaged 1.1 X 10(10) l/mol in healthy tissue and, with the exception of papillary carcinoma which showed some reduction, was not significantly altered in the various disease states studied. No receptors with low binding affinity were found. The number of receptors was significantly greater in toxic diffuse goitre and in hyperfunctioning follicular adenoma (but these tissues came from patients given antithyroid drugs and often iodine preoperatively), and was reduced in Hashimoto's thyroiditis. In well-differentiated thyroid carcinoma, the number of receptors was similar to or greater than in normal tissue, but in undifferentiated and medullary carcinoma, and in lymphoma of the thyroid, receptors were completely absent. Tracer-binding data obtained with human TSH were uniformly lower than the corresponding data obtained with bovine TSH, but showed an analogous pattern of differences amongst the various normal and pathological tissues.

Humans↗

PubMed1981

Comparison of binding of bovine and human thyroid-stimulating hormone to receptor sites on human thyroid membranes.

The binding of 125I-labelled bovine TSH (bTSH) to a wide range of human thyroid membrane preparations was compared with that of 125I-labelled human TSH (hTSH). Much higher binding percentages were obtained with the 125I-labelled bTSH. This was because the receptors had a higher binding affinity for bTSH than for hTSH. No differences in tracer purity, nor differences in optimal conditions for the binding of bTSH or hTSH, nor tracer degradation contributed significantly to the better binding of 125I-labelled bTSH. Good correlation was found between binding percentages for 125I-labelled bTSH and 125I-labelled hTSH over the range of thyroid specimens. Useful information on human TSH receptors is, therefore, obtainable from binding studies with 125I-labelled bTSH. The TSH displacement curves yielded linear Scatchard plots whenever the tracer and displacing hormones were of the same species. The data were, therefore, consistent with a simple binding reaction between TSH and a single set of independent receptor sites.

Animals↗

PubMed1980

Pathways of transepithelial potassium movement in the epithelium of distal colon in man.

1. Methods for studying the kinetics of movement of radioactive tracers across human distal colonic epithelium have been developed for use in vivo and applied to examination of transepithelial transfers of potassium. 2. During absorption of 43K from the lumen, two potassium pools, A and B, in the epithelium were identified, having mean turnover half-times of 16 and 87 min respectively. On average about 50% of the potassium lumen-to-plasma flux and most, if not all, of the potassium plasma-to-lumen flux took place through pool A. The transcellular pathway (equated with pool B) appeared to be of relatively little significance in transepithelial movement of potassium in the human distal colon. 3. Sodium and chloride movements were unaffected when lithium was present in the luminal solution, but the potassium secretion rate was nearly trebled due to increased plasma-to-lumen flux through the fast turnover pool A. 4. The permeability of the epithelium to potassium, as judged by the plasma-to-lumen fluxes, greatly exceeded that to sodium. This appeared to depend on a special highly selective potassium channel which differed from the shunt pathway in possessing definite capacity.

Adult↗

PubMed1980

Iodination of thyroid-stimulating hormone for receptor-binding studies with human thyroid membranes: effects of specific activity and method of iodination.

Three different methods were compared for 125I-labelling of thyroid-stimulating hormone (TSH) for use in receptor-binding studies with human thyroid membranes: these were the chloramine-T, Bolton-Hunter and lactoperoxidase methods. Chloramine-T proved to be an inferior method to the other two. Iodinations to different specific activity (0.7--9.4 Bq/pg) were also compared: too high a specific activity led to reduced binding and a dramatic shift in the pH optimum for the TSH-receptor interaction. A specific acitivity of 2.5 Bq/pg should not be exceeded if binding of 125I-labelled TSH is to be representative of the binding of the natural hormone. Under these conditions, pH 7.5 was optimal for binding of TSH to its receptor. Repurification of the labelled TSH by receptor adsorption also proved to be essential.

Chloramines↗

PubMed1979

Prolonged intravenous infusion of labelled iodocompounds in the rat: [125I]iodide metabolism and effects of moderate dietary iodine deficiency.

Radio-iodide was administered by prolonged continuous intravenous infusion to rats maintained under iodine-replete conditions and in moderate iodine deficiency. A close approximation to equilibrium labelling was thereby achieved. Labelled iodocompounds extracted from various tissues were analysed by thin-layer chromatography. Moderate iodine deficiency resulted in a slight increase in the ratio of mono-iodotyrosine to di-iodotyrosine in the thyroid. No change in the ratio of tri-iodothyronine (T3) to thyroxine (T4) was found in thyroid, plasma or skeletal muscle. Faecal excretion of T3 declined appreciably relative to that of T4. Under iodine-replete conditions the ratio of thyroidal secretion rates of T3 and T4 was estimated to be more than three times higher than the ratio of these iodocompounds within the thyroid. Heterogeneity of thyroglobulin structure and function may explain these observations.

Animals↗

PubMed1979

Prolonged intravenous infusion of labelled iodocompounds in the rat: [125I]thyroxine and [125I]tri-iodothyronine metabolism and extrathyroidal conversion of thyroxine to tri-iodothyronine.

Extrathyroidal tissues of the rat were labelled to steady state by prolonged continuous intravenous infusion of 125I-labelled thyroxine (T4) or tri-iodothyronine (T3). Labelled iodocompounds extracted from various tissues were analysed by thin-layer chromatography. Signifficant amounts of labelled T3 were found in all tissues examined after infusion of [125I]T4, confirming that conversion of T4 to T3 occurs in extrathyroidal tissues of the rat. Faecal excretion of labelled T3 after [125I]T4 infusion provided an assessment of the extent of extrathyroidal conversion: about a third of the T4 was metabolized by this pathway. Extrathyroidal conversion was independently estimated to account for about a third of the total production of T3. The site of extrathyroidal conversion was established by comparing the distribution of labelled T3 after the two types of infusion: kidney and liver were both prominent sites of conversion of T4 to T3.

Animals↗

PubMed1977

Measurement of serum TSH and thyroid hormones in the management of treatment of thyroid carcinoma with radioiodine.

1. Serum levels of TSH, thyroxine (T4) and triiodothyronine (T3) have been measured during treatment and follow-up of patients with thyroid carcinoma. 2. Serum TSH and thyroid hormone levels were initially normal. Three weeks after total thyroidectomy, TSH was elevated in about 50% of patients and after a subsequent therapy dose of 131I it exceeded 30 mU/l in 90% of patients. Occasionally, TSH did not rise until after the second dose of 131I. Low serum T4 and T3 concentrations were associated with the increase of TSH. 3. Withdrawal of l-thyroxine replacement treatment in athyreotic patients for four weeks before test doses of 131I, led to falls of serum T4 and T3 concentration and a progressive rise of serum TSH after the first weeks but there was considerable variation in the final level reached. In the majority, values greater than 30 mU/l were attained despite some patients having received l-thyroxine for many years. A few patients on prolonged thyroxine maintenance had little or no increase in TSH despite considerable reduction in serum T4 and T3 concentrations. 4. The 131I concentration (muCi/g) developed in tumour tissue was also examined in relation to the serum TSH level. In general a tumour should not be considered as incapable of concentrating 131I adequately until serum TSH levels have exceeded 30 mU/l.

Humans↗

PubMed1976

Potassium transport across the distal colon in man.

1. The mechanism of potassium transport across human distal colon was investigated in twenty-two individuals without evidence of bowel disease, by using a dialysis method in conjunction with measurements of the transepithelial potential difference (p.d.). 2. Whether potassium was absorbed or secreted depended on its initial concentration in the lumen. The potassium net flux was approximately zero when the luminal potassium concentration was between 30 and 50 mmol/l. 3. Potassium secretion rate was little affected by sodium absorption rate, or by the luminal sodium concentration or by the osmolality of the luminal solution. 4. Potassium secretion rate was increased by partial substitution of other cations for sodium, in the descending order Li greater than NH4 greater than Rb greater than Na. Potassium concentration increased on average to over 80 mmol/l when lithium was in the lumen. 5. The observed transepithelial p.d. was inadequate to account for the intraluminal potassium concentrations attained, the discrepancy being most marked when ammonium or lithium was in the lumen. It is suggested that some potassium is secreted by the epithelial cells and this component of the total potassium flux into the lumen is increased when rubidium, ammonium or lithium is substituted for sodium.

Adult↗

PubMed1975

Protection problems in radionuclide therapy: the patient as a gamma-radiation source.

Estimates have been made of the rate of uptake, metabolism and excretion of radioiodine given in treatments of patients with hyperthyroidism or thyroid carcinoma. Average values for the exposures to be expected at a given distance from such patients, and the variability of such exposures, are derived from these data. The mean exposure of a patient in an adjacent bed, at 2.5 m bed spacing, following typical therapeutic doses of 131-I in the treatment of hyperthyroidism or thyroid carcinoma, is estimated to be about 0.02 or 0.08 R respectively. Variations in the metabolic parameters would increase these exposures to about 0.03 and 0.14 R, at the 90 percentile values. Exposures following treatments with 100 mCi of 198-Au, or of 300 mg days of -226Ra would be about 0.2 and 0.6 R.

Gamma Rays↗

PubMedDate not supplied

Molecular properties of the vasoactive intestinal peptide receptor in aorta and other tissues.

The molecular weight of the vasoactive intestinal peptide (VIP) receptor was assessed in bovine aorta, and rat liver, lung, and brain by covalent cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The receptor in all four tissues was found to be a single polypeptide of approximate M(r) 54,000, contradicting previous claims for substantial heterogeneity in the molecular weight of this receptor. Guanine nucleotides inhibit cross-linking of 125I-VIP to its receptor, and cross-linking with ethylene glycolbis(succinimidylsuccinate) provides further evidence for complex formation between VIP, its receptor and a guanine nucleotide-binding regulatory protein (G-protein). The precise mechanism of receptor-G-protein coupling may differ between the aorta and other tissues.

Animals↗

PubMedDate not supplied

Receptor-purified, Bolton-Hunter radioiodinated, recombinant, human epidermal growth factor: an improved radioligand for receptor studies.

We report an assessment of the applicability of the Bolton-Hunter method to the radioiodination of epidermal growth factor (EGF). Recombinant human EGF (hEGF) could be radioiodinated successfully by this method, whereas murine EGF could not. Bolton-Hunter 125I-labeled hEGF was compared with commercial 125I-labeled hEGF prepared by the chloramine-T radioiodination method. Neither radioligand was sufficiently pure for a detailed characterization of the purportedly heterogeneous pattern of binding of EGF to its receptors. A procedure based on receptor adsorption was thus developed for repurification of the Bolton-Hunter 125I-labeled hEGF. This provided a much purer radioligand suitable for detailed studies of receptor-binding heterogeneity.

Adsorption↗