PubMed Health⌕ Search

Biomedical subjects

M G Thompson

Publications and source records attributed to M G Thompson.

At least 37 records · Page 2Linked to original sources
PubMed1996

N tau-methylhistidine turnover in skeletal muscle cells measured by GC-MS.

A method that employs gas chromatography-mass spectrometry has been developed to measure N tau-methylhistidine (3-methylhistidine; 3-MH) synthesis and release from skeletal muscle myotubes in vitro. It shows excellent linearity (0.9999) over the range studied (0-4 nmol), high recovery (92.6%), and low coefficient of variation (1.6%). 3-MH release from myotubes was essentially linear over a 96-h incubation, whereas the loss of 3-MH from cell protein accelerated with increasing time, an effect due, at lest in part, to decreasing rates of total protein synthesis. When incubated in either glutamine-free or methionine-free medium for 48 h, 3-MH in cell protein and appearing in the medium were greatly reduced compared with the 48-h controls, suggesting that hypertrophy was greatly reduced. Similar but lesser trends were observed with adenosine 3',5' -cyclic monophosphate. In contrast, 12-O-tetradecanoylphorbol-13-acetate (TPA) appeared to both stimulate 3-MII synthesis and inhibit its release during a 48-h incubation. The development of this method facilitates detailed investigation into the mechanisms through which agents such as TPA regulate myofibrillar protein degradation.

Bucladesine↗
PubMed1995

Stimulation of protein and DNA synthesis in mouse C2C12 satellite cells: evidence for phospholipase D-dependent and -independent pathways.

In C2C12 myoblasts, 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated a phospholipase D (PLD) to degrade phosphatidylcholine (PC) as measured by the release of choline and an increase in the formation of phosphatidic acid (PA) (or phosphatidylbutanol [PtdBuOH] in the presence of 0.5% butanol). Exogenous PLD also stimulated choline release, PA and PtdBuOH formation. The protein kinase C (PKC) inhibitor, Ro-31-8220, and PKC downregulation significantly inhibited the effects of TPA but Ro-31-8220 had no effect on PLD action. Neither basic Fibroblast Growth Factor (bFGF) or Epidermal Growth Factor (EGF) increased PLD activity. All agonists stimulated protein synthesis during both a 90 min and a 6 hr incubation and increased RNA accretion after 6 hr. The response at 90 min was not inhibited by the transcription inhibitor, actinomycin D. Ro-31-8220 and PKC downregulation significantly inhibited all the effects of TPA. In contrast, Ro-31-8220 significantly inhibited the increase in RNA accretion elicited by PLD but had no effect on the ability of agonists other than TPA to enhance protein synthesis. All agonists also stimulated thymidine incorporation into DNA. The effects of EGF, bFGF, and PLD were rapid and transient whereas that of TPA was delayed and sustained. Ro-31-8220 and PKC downregulation significantly inhibited the response due to TPA. Furthermore, Ro-31-8220 also significantly inhibited the effects elicited by EGF and PLD but not that induced by bFGF. In differentiated myotubes, TPA and PLD, but not bFGF or EGF, again stimulated choline release and PtdBuOH formation. However, all agents failed to stimulate protein synthesis and RNA accretion. The data demonstrate the presence in C2C12 myoblasts, but not differentiated myotubes, of both a PLD-dependent and PLD-independent pathway(s) leading to the stimulation of protein synthesis, RNA accretion, and DNA synthesis.

Animals↗
PubMed1995

Evidence that protein kinase C and mitogen activated protein kinase are not involved in the mechanism by which insulin stimulates translation in L6 myoblasts.

Insulin stimulated a concentration-dependent increase in protein synthesis in L6 myoblasts which was significant at 1 nM. This response was not prevented by the transcription inhibitor, actinomycin D. The protein kinase C (PKC) inhibitor, Ro-31-8220, and downregulation of PKC by prolonged incubation of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), had no effect on the ability of insulin to stimulate protein synthesis whilst completely blocking the response to TPA. In contrast, insulin failed to enhance protein synthesis significantly in the presence of either ibuprofen, a selective cyclooxygenase inhibitor or rapamycin, an inhibitor of the 70 kDa S6 kinase. When cell extracts were prepared and assayed for total myelin basic protein kinase activity, a stimulatory effect of insulin was not observed until the concentration approached 100-fold (i.e. 100 nM) that required to elicit increases in protein synthesis. Upon fractionation on a Mono-Q column, 100 nM insulin increased the activity of 3 peaks which phosphorylated myelin basic protein. Two of these peaks were identified as the 42 and 44 kDa forms of Mitogen Activated Protein (MAP) kinase by immunoblotting. In contrast, 1 nM insulin had no effect on the activity of these peaks. The data suggest that physiologically relevant concentrations of insulin do not stimulate translation in L6 cells through either PKC or the 42/44 kDa isoforms of MAP kinase and that this response is, at least in part, mediated through the activation of the 70 kDa S6 kinase by cyclooxygenase metabolites.

Amino Acid Sequence↗
PubMed1994

Stimulation of protein synthesis and phospholipase D activity by vasopressin and phorbol ester in L6 myoblasts.

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) and vasopressin on protein synthesis and phospholipase D (PLD) activity were investigated in L6 myoblasts. TPA stimulated a concentration-dependent increase in protein synthesis (EC50 approx. 10 nM) during a 90 min incubation, but had no effect after 6 h. The maximum increase was about 15% and was mediated through changes in translation, as TPA had no effect on RNA accretion and the response was not prevented by actinomycin D. TPA also stimulated PLD activity as measured by an 8-fold increase in the formation of phosphatidylbutanol (PtdBuOH) and the release of choline (EC50 5-10 nM). In contrast to TPA, vasopressin stimulated protein synthesis (maximum increase 30%, EC50 approx. 10 nM) and RNA accretion after 6 h, but had no effect after 90 min. Vasopressin also increased PtdBuOH production 4-5-fold (EC50 approx. 0.5 nM) and choline release (EC50 approx. 1 nM). The addition of a highly purified preparation of PLD (2-10 units/ml) from Streptomyces sp. to L6 cells stimulated a concentration-dependent increase in choline release and protein synthesis after both 90 min (maximum stimulation 13%) and 6 h (maximum stimulation 12%). PLD also stimulated RNA accretion after 6 h but not 90 min. The data support a role for PLD in the regulation of protein synthesis in L6 cells.

Animals↗
PubMed1994

Recruitment challenges in studying late-life depression: do community samples adequately represent depressed older adults?

Although research on late-life depression is burgeoning, little attention has been given to the sampling and recruitment obstacles encountered in trying to enlist the participation of older adults in such studies. In this article, the authors summarize the response rates of 15 recent epidemiological studies and 100 descriptive studies examining late-life depression among community-dwelling older adults. These studies excluded approximately 25-35% of potential participants. The authors present evidence suggesting that because depressed older adults may be especially likely to refuse research invitations, researchers may overlook or underestimate important correlates of depression. In addition, the authors describe several strategies for enhancing recruitment efforts.

Aged↗
PubMed1993

Arachidonate activation of protein kinase C may be involved in the stimulation of protein synthesis by insulin in L6 myoblasts.

Insulin stimulated protein synthesis in L6 myoblasts but did not increase the labelling of DAG or the release of phosphocholine from phosphatidylcholine. The DAG lipase inhibitor, RHC 80267, more than doubled the amount of label appearing in DAG but did not stimulate protein synthesis. Even in the presence of the DAG lipase inhibitor insulin failed to have any effect on DAG labelling, and conversely RHC 80267 did not modify the insulin-induced increase in protein synthesis. These results suggest that endogenous DAG production is not involved in the stimulation of protein synthesis by insulin. However, exogenous diacylglycerols (1-oleoyl-2-acetyl glycerol and 1-stearoyl-2-arachidonoyl glycerol) both stimulated protein synthesis in L6 myoblasts. The efficacy of the former (arachidonate-free) DAG suggested that their action was by activation of protein kinase C rather than by arachidonate release and prostaglandin formation. Ibuprofen, an inhibitor of cyclo-oxygenase failed to block the effects of insulin whereas a second cyclo-oxygenase inhibitor, indomethacin had only a partial inhibitory effect. The protein kinase C (PKC) inhibitor, RO-31-8220, totally blocked the effect of insulin. Since indomethacin is also recognised to inhibit phospholipase A2, the data suggests that insulin acts on protein synthesis in myoblasts by arachidonate activation of PKC.

Animals↗
PubMed1993

Distinction between quality and quantity of problem-solving responses among depressed older women.

The purpose of this project was to investigate the extent to which depressed and nondepressed community-dwelling older women differed in their problem-solving responses to vignettes describing problematic situations common in this population. Contrary to expectations, the depressed and nondepressed older women showed an equal capacity to follow traditional problem-solving steps. There were differences, however, in the quality of solutions generated for dealing with social isolation and interpersonal conflict as judged by peer evaluators. Further work is needed in understanding the components of effective problem solving most important for adjustment to real-life difficulties.

Adaptation, Psychological↗
PubMed1993

Oxytocin receptor concentrations, inositol phosphate turnover and prostaglandin release by endometrium from ewes induced to ovulate during the early post-partum period.

Induction of ovulation early post partum in sheep is associated with a high incidence (30-40%) of premature luteolysis. The present study was designed to characterize oxytocin receptor levels, oxytocin-stimulated inositol phosphate (IP) turnover (second messenger) and oxytocin-stimulated prostaglandin F2 alpha (PGF2 alpha) release in the endometrium of post-partum ewes induced to ovulate 21 days after parturition and expected to exhibit a range of corpus luteal functions subsequently. Ovulation was induced on day 21 post partum using a controlled internal drug release device and pregnant mare serum gonadotrophin, and uterine tissues were collected on days 5, 10 or 15 of the cycle (n = 4/day). A further 12 ewes whose interval from previous parturition exceeded 150 days were similarly treated and acted as controls. Measurement of daily peripheral progesterone concentrations revealed that while all control ewes exhibited normal luteal function, abnormal luteal function was evident in two, two and one post-partum ewes studied on days 5, 10 and 15 of the cycle respectively. Oxytocin receptor binding was detected (by receptor-binding assay and in-vitro autoradiography) in the endometrium and myometrium of post-partum ewes at all three stages of the oestrous cycle but only at day 15 in control ewes. To determine IP turnover, 100 mg caruncular endometrium was incubated in duplicate for 2.5 h with 10 microCi [3H]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [3H]inositol mono-, bis- and trisphosphates were quantified.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Peer support telephone dyads for elderly women: was this the wrong intervention?

Tested a preventive intervention in which peer telephone dyads were developed for low-income, community-living, elderly women with low perceived social support. After an initial assessment, respondents were randomly assigned to either an assessment-only control or received 10 weeks of friendly staff telephone contact. After a second assessment, participants receiving the staff contact were randomly assigned to continue that contact or were paired in dyads to continue phone contact with one another. Dependent variables were measures of perceived social support, morale, depression, and loneliness. All groups, particularly the staff contact group, showed some improvement in mental health scores over time, but there were no significant differences between intervention groups, or between intervention and assessment-only control groups. The results suggest that participation in the study and in personal assessment interviews at home were probably morale enhancing, and that additional telephone contact did not significantly add to that effect. Evidence also indicates that, in this sample, low perceived family support was significantly related to poor mental health, so it is possible that a program designed to increase friend support may have been the wrong intervention.

Aged↗
PubMed1991

Support interventions for older adults: confidante relationships, perceived family support, and meaningful role activity.

The rationale and problems encountered in implementing a peer-support telephone intervention are described. The research conducted by Heller, Thompson, Trueba, Hogg, and Vlachos-Weber (1991) was based on epidemiological literature documenting the moral enhancing value of confidante relationships. However, that literature may be insufficiently precise to form the basis for an intervention without prior ethnographic study of the local target population. Furthermore, the positive effects of peer friendships may refer to long established relationships rather than to newly formed social ties. It is concluded that future support intervention research with older adults should concentrate on reinforcing meaningful role activities, and that greater attention should be given to strengthening indigenous ties before attempting to create new ones. While prior process research and formative evaluation are of value, we also emphasize the importance of well-controlled field studies in the ultimate test of intervention hypotheses.

Aged↗
PubMed1991

Doxorubicin interactions at the membrane: evidence for a biphasic modulation of inositol lipid metabolism.

Doxorubicin, when incubated for 30 minutes with [32P]-labelled human erythrocyte membrane vesicles, produced an elevation of [32P]inositol-1,4,5-trisphosphate levels. The maximum rise was obtained with 10(-8) mol/l doxorubicin [132 (S.E. 13%) of control, n = 6, P = 0.001]. However, when the inositol lipids were examined, there was no evidence that doxorubicin stimulated the breakdown of [32P]phosphatidylinositol-4,5-bisphosphate under resting conditions, suggesting that the elevated levels of [32P]inositol 1,4,5-trisphosphate were not the result of the stimulation of phospholipase C. Instead, it was found that the dephosphorylation of inositol 1,4,5-trisphosphate by a 5'-phosphomonoesterase was partially inhibited by 10(-8) mol/l doxorubicin so that the rise in [32P]inositol 1,4,5-trisphosphate resulted from the inhibition of the breakdown of constitutively released [32P] inositol 1,4,5-trisphosphate. Similar data was also obtained with another aminoglycoside antibiotic, neomycin. The release of [32P] inositol 1,4-bisphosphate and [32P] inositol 1,4,5-trisphosphate and the breakdown of the inositol lipids in response to calcium (2.5 x 10(-4) and 10(-3) mol/l) stimulation was enhanced by doxorubicin (10(-6) to 10(-12) mol/l). These effects on resting and stimulated inositol lipid metabolism are discussed with reference to the paradoxical effects of doxorubicin to both stimulate and inhibit proliferation, according to concentration.

Calcium↗
PubMed1990

Elevation of leukemic cell intracellular calcium by the ether lipid SRI 62-834.

SRI 62-834 is a novel antineoplastic ether lipid which is currently undergoing a Phase 1 clinical trial in the United Kingdom. Its mechanism of action has not been defined. Incubation of 7.5 X 10(6)/ml HL-60 human myelomonocytic leukemia cells with between 10 and 50 microM SRI 62-834 brought about a concentration-dependent, biphasic rise in intracellular calcium, as measured by the calcium-sensitive fluorescent dye Quin-2 AM. Incubation with 30 microM SRI 62-834 elevated intracellular calcium from 110 to 415 nM after 10 min in a typical experiment; this concentration inhibited cell growth by greater than 90% (50% inhibition of growth was observed at 8 microM). The calcium channel blockers verapamil and prenylamine did not inhibit the SRI 62-834-induced elevation of intracellular calcium. Incubation of SRI 62-834 with K562 erythroblastic leukemia cells also brought about a rise in the intracellular calcium. The growth of K562 cells was less sensitive to SRI 62-834 (dose to produce 50% growth inhibition, 65 microM) compared to HL-60 cells, and significant intracellular calcium rises, which were monophasic, required greater than 40 microM SRI 62-834. At a concentration of SRI 62-834 which inhibited both HL-60 and K562 growth by 90% (30 and 140 microM, respectively) an equivalent rise in intracellular calcium was observed (circa 400 nM). Preincubation of HL-60 or K562 cells with 1 to 100 nM 12-O-tetradecanoylphorbol-13-acetate for 10 min prior to the addition of SRI 62-834 inhibited the rise in intracellular calcium in a concentration-dependent manner. It is suggested that SRI 62-834-induced changes in intracellular calcium may contribute to its cytotoxicity and that the rise is not due to an early and grossly disruptive effect of the agent on membrane structure.

Aminoquinolines↗
PubMed1990

Facets of support related to well-being: quantitative social isolation and perceived family support in a sample of elderly women.

The purpose of this study was to examine the independent and interactive relationships of measures of network embeddedness and perceived social support with mental and physical health measures from responses of a sample of 271 community-dwelling elderly women. Quantitative social isolation was measured as the co-occurrence of low network embeddedness with family and with friends. There was a threshold effect such that quantitatively isolated participants had poorer psychological well-being and functional health than did nonisolated participants. This effect was independent of perceived support levels. The pattern was different for perceived social support. Elderly women with low perceived family support had poorer psychological well-being regardless of perceived support from friends or network embeddedness. Implications are discussed for several unanswered questions in the social support literature, including possible interventions for the quantitatively isolated and for those with low levels of perceived support.

Aged↗
PubMed1990

Effect of gastrin-releasing peptide on the secretion of mouse islet hormones in vitro.

Collagenase-isolated mouse islets were incubated with gastrin-releasing peptide (GRP). At 5.6 mmol glucose/l. 10 nmol GRP/l increased the release of insulin (by 50%) and glucagon (by twofold), decreased the release of pancreatic polypeptide (by 35%), but did not significantly affect the release of somatostatin. At 16.7 mmol glucose/l, 10 nmol GRP/l increased glucagon release (by fivefold) and decreased pancreatic polypeptide release (by 46%), without significantly altering insulin and somatostatin release. GRP (200 nmol/l) did not affect insulin release by perifused mouse islets at 2.8 mmol glucose/l, but increased both first and second phase insulin release after a square wave increase in the glucose concentration to 11.1 mmol/l. At 5.6 mmol glucose/l, GRP (100 pmol/1-100 nmol/l) increased (by 50-70%) insulin release by the RINm5F clonal cell line. GRP did not affect glucose oxidation or the cyclic adenosine monophosphate content of RINm5F cells. However, the intracellular free Ca2+ concentration of RINm5F cells was rapidly and transiently increased by GRP (maximum increase of 64% about 10 s after exposure to 1 mumol GRP/l). The rise of intracellular free Ca2+ was approximately halved in the absence of extracellular Ca2+. The results suggest that GRP may contribute to the normal regulation of the endocrine pancreas. The insulin-releasing effect of GRP is mediated via increased cytosolic free Ca2+, derived both from an increased net influx of extracellular Ca2+ and from mobilization of intracellular Ca2+ stores.

Animals↗
PubMed1987

Inhibition of human erythrocyte inositol lipid metabolism by adriamycin.

Incubation of human erythrocytes with Adriamycin prevented their morphological transition from discocytes to echinocytes when they were either depleted of ATP or loaded with calcium. This effect was dependent upon drug concentration and cell density. Adriamycin (10(-5) M) prevented, by greater than 90%, the echinocytosis of 10(7) cells/ml (S. B. Chahwala and J. A. Hickman, Cancer Res., 45: 4986-4989, 1985), and 5 X 10(-4) M prevented that of 10(9) cells/ml. There was a poor correlation between the effects of Adriamycin as a modulator of this morphological transition and its potency as an inhibitor of calmodulin. Using inside-out red blood cell vesicles, Adriamycin inhibited calmodulin dependent Ca2+ uptake with a 50% inhibitory concentration of 5 X 10(-4) M. Adriamycin thus differs from other amphipathic drugs, such as those of the phenothiazine class, where inhibition of calmodulin correlated well with effects on erythrocyte morphology (G. A. Nelson, M. L. Andrews, and M. J. Karnovsky, J. Cell Biol., 96: 730-735, 1983). After 12 h of ATP depletion, levels of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] extracted from 10(9) erythrocytes/ml fell by 57% and after 48 h they fell by 97%, changes which were coincident with a 100% transition of morphology to echinocytes. Adriamycin, 5 X 10(-4) M-1 X 10(-3) M, maintained 10(9) cells/ml in a discocyte morphology and maintained PtdIns(4,5)P2 levels at 60-70% of the time zero controls, independently of the size of the fall in PtdIns(4,5)P2 levels. The data suggested that Adriamycin inhibited a discrete pool of PtdIns(4,5)P2 which may be responsible for the maintenance of a discocyte morphology. Neomycin, 10(-3) M, had no effect on the ATP depletion-induced discocyte-echinocyte transition of 10(9) erythrocytes/ml or on the fall in PtdIns(4,5)P2 levels. Adriamycin, like neomycin, prevented the calcium-induced breakdown of erythrocyte membrane vesicle PtdIns(4,5)P2 to inositol trisphosphate (50% inhibitory concentration, 7 X 10(-4) M) but, unlike neomycin (50% inhibitory concentration, 4.25 X 10(-4) M) it was able to inhibit breakdown by 100% at higher concentrations.

Adenosine Triphosphate↗
PubMed1987

The effect of phorbol esters on human erythrocyte morphological discocyte-echinocyte transitions.

12-O-Tetradecanoylphorbol-13-acetate (TPA) (100 nM) when incubated with human erythrocytes under conditions of ATP depletion, delayed the onset of the morphological transition from discocytes to echinocytes so that at 2 h, when control incubations were estimated to contain 65% echinocytes, those treated with TPA contained 23% echinocytes. TPA did not alter the subsequent rate of the transition which was complete by 3 h in control cells and 5 h in TPA-treated cells. Addition of 100 nM TPA to ATP-depleted erythrocytes at 2.5 h (greater than 80% echinocytes) for 0.5 h at 37 degrees C resulted in 17% reversal to a discocyte morphology, but as the time of incubation under conditions of ATP depletion was extended, the level of the reversal fell. TPA had no significant effect on the fall in ATP concentrations over the time course of the experiments (5 h). Preincubation of discocytes with TPA for 10 min also prevented, by approx. 50%, the echinocytosis induced by the calcium (0.2 mM) loading of discocytes using 5 microM A23187. TPA was unable to reverse the echinocyte morphology of calcium-loaded cells back to discocytes. The less potent tumour promotor 4-phorbol-12,13-didecanoate had no effect on this discocyte-echinocyte transition. Incubation of discocytes with the diacylglycerol 1-oleoyl-2-acetylglycerol (OAG) (1-10 microM) had complex effects on morphology, and the ATP-induced morphological transition, ranging from stomatocyte formation to echinocyte formation, depending upon the concentration of the agent and the time of incubation.

Adenosine Triphosphate↗