[Post-traumatic anorexia: challenging multidisciplinary management].
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Adolescent↗
Biomedical subjects
M Dura
Publications and source records attributed to M Dura.
Regulation of dynamic behavior of cardiac ryanodine receptor by Mg2+ under simulated physiological conditions.
Mg2+, an important constituent of the intracellular milieu in cardiac myocytes, is known to inhibit ryanodine receptor (RyR) Ca2+ release channels by competing with Ca2+ at the cytosolic activation sites of the channel. However, the significance of this competition for local, dynamic Ca2+-signaling processes thought to govern cardiac excitation-contraction (EC) coupling remains largely unknown. In the present study, Ca2+ stimuli of different waveforms (i.e., sustained and brief) were generated by photolysis of the caged Ca2+ compound nitrophenyl (NP)-EGTA. The evoked RyR activity was measured in planar lipid bilayers in the presence of 0.6-1.3 mM free Mg2+ at the background of 3 mM total ATP in the presence or absence of 1 mM luminal Ca2+. Mg2+ dramatically slowed the rate of activation of RyRs in response to sustained (> or =10-ms) elevations in Ca2+ concentration. Paradoxically, Mg2+ had no measurable impact on the kinetics of the RyR response induced by physiologically relevant, brief (<1-ms) Ca2+ stimuli. Instead, the changes in activation rate observed with sustained stimuli were translated into a drastic reduction in the probability of responses. Luminal Ca2+ did not affect the peak open probability or the probability of responses to brief Ca2+ signals; however, it slowed the transition to steady state and increased the steady-state open probability of the channel. Our results indicate that Mg2+ is a critical physiological determinant of the dynamic behavior of the RyR channel, which is expected to profoundly influence the fidelity of coupling between L-type Ca2+ channels and RyRs in heart cells.
Animals↗
Kinetics of cardiac RyR channel gating studied at high temporal resolution.
Measurements of ryanodine receptor (RyR) activity during dynamic changes of calcium concentration have suggested that RyR has at least four calcium binding sites, and that activation transpires as an increase in the activity within the high open probability H-mode. Binding of several Ca2+ ions within the H-mode should manifest itself in the steady-state RyR activity by the presence of multiple closed times. However, previously only two closed times were detected in the H-mode of RyR activity. Here we recorded steady-state activity of single cardiac RyRs with high temporal resolution and compared it to data simulated under the same conditions using our previously published model of RyR gating. At a 10 kHz resolution, the closed time histograms of both experimental and simulated data had three exponential components. The closed times of simulated data were not significantly different from those obtained experimentally. After filtering at 2 kHz, only two exponential closed time components with time constants not significantly different from those previously published could be detected in both experimental and simulated records. The conformity of the steady-state experimental data to the model derived from the dynamic data provides further support for the idea that RyRs need binding of multiple Ca2+ ions to open.
Animals↗
Modal gating transitions in cardiac ryanodine receptors during increases of Ca2+ concentration produced by photolysis of caged Ca2+.
Channel adaptation is a basic property of the sarcoplasmic reticulum Ca2+-release channels/ryanodine receptors (RyRs). It allows channel activity to decay during sustained increases in the concentration of activating Ca2+. Despite the potential physiological importance of this self-confining process, its molecular mechanism is not well understood. To define the mechanism of adaptation we studied the dynamics of cardiac Ca2+-release channel (RyR) gating using the planar lipid bilayer technique in combination with photolysis of caged Ca2+ (DM-nitrophen). Channels activated by rapid and sustained increases in Ca2+ concentration (from 0.1 to 0.5 micromol/l) displayed three distinct gating modes, manifested as current records with frequent and long openings (H-mode), with rare and short openings (L-mode), and with no openings (I-mode). H-mode channel activity occurred primarily at early times while L- and I-modes predominated at late times after the rapid Ca2+ concentration increase. The decrease in probability of H-mode, mirrored by an increase in the probability of the I-mode, proceeded with a time constant similar to that observed for spontaneous decay in channel activity (i.e., adaptation) in ensemble average records. These results indicate that RyR adaptation transpires by a shift of channel gating from a high open probability mode to low open probability and inactivated modes of the channel.
Animals↗
Heterogeneity of urinary steroid profiles in children with adrenocortical tumors.
The excretory patterns of urinary steroids determined by capillary gas chromatography in 11 children (aged 0.8-16.5 years) with adrenocortical tumors were established. In 8 patients the predominant clinical feature was virilization, in 3 others, Cushing's syndrome. In 5 patients (3 carcinoma, 2 adenoma) very high excretion of 3 beta-hydroxy-5-ene steroids was observed. In 2 others (adenomas) only moderately elevated excretion of 11 beta-hydroxyandrosterone was found. In 1 patient (adenoma) pregnanediol dominated in the steroid profile, accompanied by moderately elevated 3 beta-hydroxy-5-ene steroids. Out of 3 Cushingoid patients (1 carcinoma, 2 adenomas), 1 presented an atypical urinary steroid pattern for hypercortisolemia, without 5 alpha-reductase and 11 beta-hydroxysteroid dehydrogenase deficiencies. Neither the urinary steroid pattern nor tumor size alone were reliable indicators of tumor malignancy, as evaluated by a pathological examination and subsequent metastasis-free survival.
Adenoma↗