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M Baptist

Publications and source records attributed to M Baptist.

11 recordsLinked to original sources
PubMed2006

Cerebral autoregulation is impaired in cardioinhibitory carotid sinus syndrome.

OBJECTIVES: To compare changes in cerebral autoregulation in response to controlled, lower body negative pressure-induced hypotension in patients with carotid sinus syndrome (CSS) and case controls. DESIGN: Prospective case controlled study. SETTING: Secondary and tertiary referral falls and syncope service. PATIENTS: 17 consecutive patients with CSS and 11 asymptomatic controls. INTERVENTIONS: Hypotension insufficient to cause syncope induced by lower body negative pressure (minimum 30 mm Hg fall in systolic blood pressure (SBP)) during concomitant transcranial Doppler ultrasonography. MAIN OUTCOME MEASURES: Cerebral autoregulation (systolic, diastolic and mean middle cerebral arterial blood flow velocities and cerebrovascular resistance) with continuous end-tidal carbon dioxide and haemodynamic monitoring. RESULTS: Cerebral autoregulatory indices differed significantly between patients with CSS and controls. Systolic, diastolic and middle cerebral arterial blood flow velocities were, respectively, 9.2 m/s (95% confidence interval (CI) 2.9 to 15.4 m/s), 4.7 m/s (95% CI 1.5 to 7.9 m/s) and 6.9 m/s (95% CI 2.5 to 11.4 m/s) slower in patients with CSS. Cerebrovascular resistance was significantly greater in patients with CSS than in controls at SBP nadir and suction release; differences were 0.9 mm Hg/m/s (95% CI 0.0 to 1.7 mm Hg/m/s) and 0.8 mm Hg/m/s (95% CI 0.0 to 1.7 mm Hg/m/s), respectively. End-tidal carbon dioxide and systemic haemodynamic variables were similar for patients and controls at baseline and during lower body negative pressure. CONCLUSIONS: Cerebral autoregulation is altered in patients with CSS. This difference may have aetiological implications in the differential presentation with falls and drop attacks rather than syncope.

Aged↗
PubMed1996

Expression and subcellular localization of CDK2 and cdc2 kinases and their common partner cyclin A in thyroid epithelial cells: comparison of cyclic AMP-dependent and -independent cell cycles.

Dog thyroid epithelial cells in primary culture constitute a model of positive control of DNA synthesis initiation and G0-S prereplicative phase progression by cyclic AMP as a second messenger for TSH. In tis early steps, this mitogenic control is quite distinct from cyclic AMP-independent mitogenic cascades elicited by growth factors. We demonstrate here that TSH (cyclic AMP) and EGF+serum (cyclic AMP-independent) stimulations cooperate and finally converge on proteins that control the cell cycle machinery. This convergence included a common induction of the expression of cyclin A and p34cdc2, and to a lesser extent of p33/38cdk2, which was already expressed in quiescent thyroid cells, and common changes of cdc2 and CDK2 phosphorylations as evidenced by electrophoretic mobility shifts. Kinetic differences in these processes after stimulation by TSH or EGF+serum or by these factors in combination correlated with differences in cell cycle kinetics. Moreover, an immunofluorescence analysis of these proteins using the double labeling of PCNA as a marker of each cell cycle phase shows: (1) a previously undescribed nuclear translocation of CDK2 before S phase initiation; (2) a sudden increase of cdc2 nuclear immunoreactivity at G2/mitosis transition. These data support the roles of CDK2 and cdc2 at G1/S and G2/mitosis transitions, respectively. (3) We were unable to demonstrate in individual cells a strict association between the nuclear appearance of cyclin A and G1/S transition, and an association of cyclin A and CDK2 with PCNA-stained DNA replication sites. On the other hand, the lengthening of G2 phase in the TSH/cyclic AMP-dependent thyroid cell cycle was associated with a stabilization of Tyr15 inhibitory phosphorylation of cdc2 and an especially high nuclear concentration of cyclin A and CDK2. We hypothesize that high nuclear accumulation of cyclin A and CDK2 during G2 phase could be causative in the cyclic AMP-dependent delay of mitosis onset.

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PubMed1995

Intercellular heterogeneity of early mitogenic events: cAMP generalizes the EGF effect on c-Fos protein appearance but not on MAP kinase phosphorylation and nuclear translocation in dog thyroid epithelial cells.

When quiescent dog thyroid epithelial cells in primary culture are stimulated for 48 h with thyrotropin (TSH), forskolin acting through cAMP, or with cAMP-independent mitogens including epidermal growth factor (EGF), hepatocyte growth factor (HGF), and a tumor promoting phorbol ester (TPA), only 30-60% of cells progress through the cell cycle. A more general growth response requires the combination of EGF and TSH or forskolin. In this study we ask whether this intercellular heterogeneity in mitogen sensitivity could depend on a similar heterogeneity at early stages of the mitogenic stimulation process, i.e., at the levels of p42/p44 MAP kinase nuclear translocation and c-Fos protein appearance. We used indirect immunofluorescence microscopy with photometric quantitation and corroborated data using Western blotting. We analyzed the double staining of c-Fos and p42/p44 MAP kinases, since the nuclear translocation of these MAP kinases has been suggested as a key step for the stimulation of c-fos transcription. (i) EGF and HGF induced c-Fos accumulation and MAP kinase translocation in variable fractions of the cell population that corresponded to their relative potency as mitogens. c-Fos appearance and MAP kinase translocation poorly correlated in individual cells. Many cells accumulated c-Fos without any detectable p42/p44 MAP kinase translocation. The heterogeneity of proliferative responses to EGF could be due to the lack of c-Fos or MAP kinase responsiveness of many cells. (ii) TPA induced c-Fos accumulation and MAP kinase translocation within the whole cell population, which did not explain the heterogeneity of the growth response to this factor and showed that these events are not sufficient to elicit DNA synthesis, (iii) TSH and forskolin induced a weak c-Fos accumulation in only a minority of cells but, as previously shown, no p42/p44 MAP kinase phosphorylation and translocation. An important c-Fos expression was thus dispensable for the strong DNA synthesis stimulation exerted by cAMP-dependent mitogens. (iv) Forskolin potentiated the EGF effect on c-Fos expression but not on p42/p44 MAP kinase phosphorylation and translocation. This reflected the fact that EGF induced c-Fos accumulation in 90% of cells in the presence of forskolin but in 30-50% of cells in its absence. This kind of potentiation, which specifically implies an increase in the fraction of responding cells, is termed "generalization" in the present study.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1993

Phosphorylation of mitogen-activated protein kinases is involved in the epidermal growth factor and phorbol ester, but not in the thyrotropin/cAMP, thyroid mitogenic pathway.

In dog thyroid epithelial cells (thyrocytes) in primary culture, thyrotropin (TSH) acting through cAMP induces proliferation and differentiation expression, whereas epidermal growth factor (EGF) and tumor-promoting phorbol esters induce proliferation and dedifferentiation. In these cells we have demonstrated mitogen-activated protein (MAP) kinase phosphorylation by 32P labeling and two-dimensional gel electrophoresis and by immunodetection with anti-MAP kinase and anti-phosphotyrosine antibodies after one- or two-dimensional gel electrophoresis. MAP kinase localization was demonstrated by immunochemical staining. We show the following results. (i) As in other systems, EGF and phorbol esters induced p42 and p44 MAP kinases phosphorylation on tyrosine, serine, and threonine. This effect was rapid, peaking after 5 and 15 min, respectively, followed by a slow decline thereafter. It preceded a translocation of MAP kinase immunoreactivity from cytoplasm to nucleus. (ii) Carbamylcholine, a potent stimulator of the Ca(2+)-phosphatidylinositol cascade which is unable to induce DNA synthesis, stimulated MAP kinases phosphorylation and nuclear staining with kinetics similar to those observed after EGF action, indicating that MAP kinase phosphorylation was not sufficient for mitogenesis. (iii) The cAMP-dependent mitogenic cascade elicited by TSH and forskolin did not involve the phosphorylation and nuclear translocation of p42 and p44 MAP kinases at any time during the entire prereplicative phase. Activation of MAP kinases by phosphorylation is therefore not a necessary step in the G0-G1 transition in this mitogenic cascade.

Animals↗
PubMed1993

Demonstration of cell cycle kinetics in thyroid primary culture by immunostaining of proliferating cell nuclear antigen: differences in cyclic AMP-dependent and -independent mitogenic stimulations.

In this study, experimental conditions are described that allowed us to follow the fate of the DNA polymerase delta-associated proliferating cell nuclear antigen (PCNA), by immunolabeling during the overall cell cycle. Differences in subcellular localization or the presence of PCNA allowed us to identify each phase of the cell cycle. Using these cell cycle markers in dog thyroid epithelial cells in primary culture, we found unexpected differences in cell cycle kinetics, in response to stimulations through cAMP-dependent and cAMP-independent pathways. These provide a new dimension to the view that the two pathways are largely separate, but co-operate on DNA synthesis initiation. More precisely, thyrotropin (TSH), acting via cAMP, exerts a potent triggering effect on DNA synthesis, associated with a precocious induction of PCNA appearance. This constitutes the major influence of TSH (cAMP) in determining cell cycle progression, which is only partly moderated by TSH-dependent lengthening of S- and G2-phases.

Animals↗
PubMed1992

A mechanism generating heterogeneity in thyroid epithelial cells: suppression of the thyrotropin/cAMP-dependent mitogenic pathway after cell division induced by cAMP-independent factors.

The mechanisms that generate the intercellular heterogeneity of functional and proliferation responses in a tissue are generally unknown. In the thyroid gland, this heterogeneity is peculiarly marked and it has been proposed that it could result from the coexistence of genetically different subpopulations of thyrocytes. To evaluate the heterogeneity of proliferative responses in primary culture of dog thyrocytes, we asked whether the progeny of cells having incorporated 3H thymidine in a first period of the culture could have a distinct proliferative fate during a second labeling period (incorporation of bromodeoxyuridine revealed by immunofluorescence staining combined with autoradiography of 3H thymidine). No growth-prone subpopulations were detected and the great majority of cells were found to response to either EGF or thyrotropin (TSH) through cAMP. However, only a fraction of cells replicated DNA at one given period and a clustered distribution of labeled cells within the monolayer, which was different for thymidine- or bromodeoxyuridine-labeled cells, indicates some local and temporal synchrony of neighboring cells. The TSH/cAMP-dependent division of thyrocytes preserved their responsiveness to both TSH and EGF mitogenic pathways. By contrast, cells that had divided during a momentary treatment with EGF lost the mitogenic sensitivity to TSH and cAMP (forskolin) but retained the sensitivity to EGF. Since cells that had not divided kept responsiveness to both TSH and EGF, this generated two subpopulations differing in mitogen responsiveness. The extinction of the TSH/cAMP-dependent mitogenic pathway was delayed (1-2 d) but stable. Cell fusion experiments suggest it was due to the induction of a diffusible intracellular inhibitor of the cAMP-dependent growth pathway. These findings provide a useful model of the generation of a qualitative heterogeneity in the cell sensitivity to various mitogens, which presents analogies with other epigenetic processes, such as differentiation and senescence. They shed a new light on the significance of the coexistence of different modes of cell cycle controls in thyroid epithelial cells.

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PubMed1991

Various facets of the intercellular heterogeneity in thyroid primary culture.

The mechanisms that generate the intercellular heterogeneity of functional and proliferation responses in a tissue are generally unknown. In thyroid gland, this heterogeneity is peculiarly marked and it was suggested that it could result from the coexistence of (epi)genetically different subpopulations of thyrocytes. As summarized in this short review, qualitative or quantitative intercellular heterogeneities have been found at each levels of our "in situ" investigations of morphological, differentiation and proliferative responses of unselected dog thyrocytes in primary culture. These different heterogeneities are unrelated at the individual cell level, which does not indicate the coexistence in thyroid of cell subpopulations stably expressing special properties. Nevertheless, using a double labeling methodology that allows to trace the proliferative behavior of some cells, we show how cell division may stably affect further proliferation responses and how a local synchrony of the dividing cells can result in a stable heterogeneity with a regional, patchy pattern, which resembles the one characterizing multinodular goiter.

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