Inhibition of myogenic differentiation in proliferating myoblasts by cyclin D1-dependent kinase

Although the myogenic regulator MyoD is expressed in proliferating myoblasts, differentiation of these cells is limited to the G0 phase of the cell cycle. Forced expression of cyclin D1, but not cyclins A, B, or E, inhibited the ability of MyoD to transactivate muscle-specific genes and correlated with phosphorylation of MyoD. Transfection of myoblasts with cyclin-dependent kinase (Cdk) inhibitors p21 and p16 augmented muscle-specific gene expression in cells maintained in high concentrations of serum, suggesting that an active cyclin-Cdk complex suppresses MyoD function in proliferating cells.

Correlation of terminal cell cycle arrest of skeletal muscle with induction of p21 by MyoD

Skeletal muscle differentiation entails the coordination of muscle-specific gene expression and terminal withdrawal from the cell cycle. This cell cycle arrest in the G0 phase requires the retinoblastoma tumor suppressor protein (Rb). The function of Rb is negatively regulated by cyclin-dependent kinases (Cdks), which are controlled by Cdk inhibitors. Expression of MyoD, a skeletal muscle-specific transcriptional regulator, activated the expression of the Cdk inhibitor p21 during differentiation of murine myocytes and in nonmyogenic cells. MyoD-mediated induction of p21 did not require the tumor suppressor protein p53 and correlated with cell cycle withdrawal. Thus, MyoD may induce terminal cell cycle arrest during skeletal muscle differentiation by increasing the expression of p21.

Postoperative evaluation of pulmonary arteries in congenital heart surgery by magnetic resonance imaging: comparison with echocardiography

Palliative and corrective operations for the treatment of cyanotic congenital heart disease frequently involve or potentially influence the size of the pulmonary arteries. Echocardiography and magnetic resonance imaging (MRI) are two noninvasive imaging techniques currently used to assess morphologic abnormalities of the pulmonary arteries. The purpose of this study was to evaluate the role of MRI in comparison with echocardiography for defining morphologic changes of the pulmonary arteries after congenital heart surgery. The MRI scans and echocardiograms of 33 patients with surgery involving or affecting the pulmonary arteries were compared. The pulmonary outflow tract, pulmonary confluence, right and left pulmonary arteries, and surgical shunts were separately evaluated. Cineangiography and surgical reports were used to confirm findings. MRI and echocardiography were equivalent for demonstrating abnormalities of the right ventricular outflow tract, main pulmonary artery, and a variety of pulmonary shunts. MRI was superior to echocardiography in demonstrating abnormalities of the right and left pulmonary arterial branches (p < 0.001). MRI is effective for monitoring pulmonary arterial status after surgery and is superior to echocardiography for the evaluation of the right and left pulmonary arteries.

MRI vs echocardiography in the evaluation of the Jatene procedure

OBJECTIVE

Effective, noninvasive imaging studies are essential in the long-term assessment of patients who have had surgical correction of congenital heart disease. The initial study in most patients is echocardiography. The objective of the current study was to define the additional information that might be provided by MRI in comparison to echocardiography.

MATERIALS AND METHODS

Electrocardiogram-gated MRI was used to evaluate 12 patients (mean age 4.5 years) who had undergone the Jatene (arterial switch) procedure for transposition of the great arteries. Magnetic resonance imaging and two-dimensional echocardiography were compared for their ability to demonstrate common complications of this procedure, namely, focal stenoses of the aortic and pulmonary anastomoses, right ventricular outflow tract, and both branch pulmonary arteries.

RESULTS

A total of 24 focal stenoses were detected by MRI and echocardiography. The MR detected 22 of these (92%) and echocardiography detected 14 (58%). Ten of 17 stenoses involving the branch pulmonary arteries were identified only by MR.

CONCLUSION

These results indicate that MRI is effective in evaluating post-operative complications of the pulmonary arteries in patients who have undergone the Jatene procedure and can provide information additive to echocardiography in these patients.

Plasma levels of peptide YY correlate with cisplatin-induced emesis in dogs

The effect of cisplatin on plasma peptide YY (PYY) and 5-hydroxytryptamine (5-HT) concentrations was determined in conscious dogs (n = 6 per group) pretreated with either saline, or the 5-HT3-receptor antagonists ondansetron or granisetron. Cisplatin (3.0 mg kg-1, i.v.) caused emesis (18.8 +/- 2.9 episodes; 75-284 min) and significantly increased the mean area under the curve (AUC) over a 6-h period of plasma PYY concentrations (7.4 +/- 1.8 to 11.5 +/- 3.7 ng) in all saline-pretreated dogs, whereas the mean AUC of plasma 5-HT concentrations did not significantly increase (34.7 +/- 7.4 vs 35.6 +/- 12.3 pM h). The concentrations of PYY correlated closely with the incidence of emesis (r = 0.99). In animals pretreated (36 min) with ondansetron (0.316 mg kg-1, i.v.) or granisetron (0.316 mg kg-1, i.v.), the number of cisplatin-induced emetic episodes was significantly (P < 0.005) decreased compared with control. In animals receiving cisplatin and pretreated with ondansetron, PYY concentrations were not significantly altered, whereas the mean AUC of plasma concentrations of 5-HT over 6 h increased (35.6 +/- 12.3 to 82.3 +/- 34.6 pM h; P < 0.05). In animals receiving cisplatin and pretreated with granisetron, plasma concentrations of 5-HT were not significantly altered, whereas the mean AUC of plasma PYY concentrations were significantly reduced compared with control (6.2 +/- 1.7 vs 11.5 +/- 3.7 ng h).(ABSTRACT TRUNCATED AT 250 WORDS)

Synaptic repression at crayfish neuromuscular junctions. I. Generation after partial target area removal

Synaptic repression, the inability of synaptic junctions to generate normal-sized postsynaptic potentials under normal physiological conditions, is reported here for crayfish neuromuscular synapses. The synapses in the superficial flexor muscle system of the crayfish change their efficiency in generating a postsynaptic response as a result of a specific alteration in their immediate environment. When the superficial flexor nerve is cut halfway into the target muscle field and the lateral muscle fibers are removed, the intact medial synapses do not generate normal-sized junction potentials (JP) at the 17 degrees-19 degrees C temperature of the Ringers solution. JPs cannot be recorded in 83% of the muscle fibers at 2 weeks after the operation and of the few JPs that can be detected, 80% are smaller than 1 mV in size. By 8 weeks after the operation, JPs were detected in 55% of the muscle fibers, and now only 46% of these are smaller than 1 mV. When the lateral muscle fibers are left in place during the original operation, providing a target area for the cut nerve to grow into, JPs were then detected in 60%-80% of all medial fibers at all time periods after the operation; their size profile, with 10%-25% of the muscle fibers having JP's less than 1 mV, was similar to control values. These results suggest that the efficiency of these synaptic contacts become affected as a result of partial axotomy and removal of the target area of the cut branches of the axons.

Simultaneous analysis of 25 pesticides in crops using gas chromatography and their identification by gas chromatography-mass spectrometry

The simultaneous analysis of 25 pesticides in soy beans and rices was performed by gas chromatography with dual electron-capture detection and nitrogen-phosphorus detection. The pesticides were extracted from the samples with solvent and the Bio-Beads S-X3 clean-up procedure was used. Recovery studies were performed at the 1-ppm level of pesticides added to each crop. Their recoveries ranged between 83 and 105% with coefficient of variations of 0.5-8.2%. The gas chromatographic properties of the 25 pesticides were also investigated. Conformation analysis was achieved by the retention time and characteristic fragment ions using the technique of gas chromatography-mass spectrometry-selected-ion monitoring.