GTP-binding protein beta gamma subunits mediate presynaptic calcium current inhibition by GABA(B) receptor.

A variety of GTP-binding protein (G protein)-coupled receptors are expressed at the nerve terminals of central synapses and play modulatory roles in transmitter release. At the calyx of Held, a rat auditory brainstem synapse, activation of presynaptic gamma-aminobutyric acid type B receptors (GABA(B) receptors) or metabotropic glutamate receptors inhibits presynaptic P/Q-type Ca(2+) channel currents via activation of G proteins, thereby attenuating transmitter release. To identify the heterotrimeric G protein subunits involved in this presynaptic inhibition, we loaded G protein beta gamma subunits (G beta gamma) directly into the calyceal nerve terminal through whole-cell patch pipettes. G beta gamma slowed the activation of presynaptic Ca(2+) currents (I(pCa)) and attenuated its amplitude in a manner similar to the externally applied baclofen, a GABA(B) receptor agonist. The effects of both G beta gamma and baclofen were relieved after strong depolarization of the nerve terminal. In addition, G beta gamma partially occluded the inhibitory effect of baclofen on I(pCa). In contrast, guanosine 5'-O-(3-thiotriphosphate)-bound G(o)alpha loaded into the calyx had no effect. Immunocytochemical examination revealed that the subtype of G proteins G(o), but not the G(i), subtype, is expressed in the calyceal nerve terminal. These results suggest that presynaptic inhibition mediated by G protein-coupled receptors occurs primarily by means of the direct interaction of G(o) beta gamma subunits with presynaptic Ca(2+) channels.

The role of GTP-binding protein activity in fast central synaptic transmission.

Guanosine 5'-triphosphate (GTP)-binding proteins (G proteins) are involved in exocytosis, endocytosis, and recycling of vesicles in yeast and mammalian secretory cells. However, little is known about their contribution to fast synaptic transmission. We loaded guanine nucleotide analogs directly into a giant nerve terminal in rat brainstem slices. Inhibition of G-protein activity had no effect on basal synaptic transmission, but augmented synaptic depression and significantly slowed recovery from depression. A nonhydrolyzable GTP analog blocked recovery of transmission from activity-dependent depression. Neither effect was accompanied by a change in presynaptic calcium currents. Thus, G proteins contribute to fast synaptic transmission by refilling synaptic vesicles depleted after massive exocytosis.

G-Protein-coupled modulation of presynaptic calcium currents and transmitter release by a GABAB receptor.

Presynaptic GABAB receptors play a regulatory role in central synaptic transmission. To elucidate their underlying mechanism of action, we have made whole-cell recordings of calcium and potassium currents from a giant presynaptic terminal, the calyx of Held, and EPSCs from its postsynaptic target in the medial nucleus of the trapezoid body of rat brainstem slices. The GABAB receptor agonist baclofen suppressed EPSCs and presynaptic calcium currents but had no effect on voltage-dependent potassium currents. The calcium current-EPSC relationship measured during baclofen application was similar to that observed on reducing [Ca2+]o, suggesting that the presynaptic inhibition generated by baclofen is caused largely by the suppression of presynaptic calcium influx. Presynaptic loading of the GDP analog guanosine-5'-O-(2-thiodiphosphate) (GDPbetaS) abolished the effect of baclofen on both presynaptic calcium currents and EPSCs. The nonhydrolyzable GTP analog guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) suppressed presynaptic calcium currents and occluded the effect of baclofen on presynaptic calcium currents and EPSCs. Photoactivation of GTPgammaS induced an inward rectifying potassium current at the calyx of Held, whereas baclofen had no such effect. We conclude that presynaptic GABAB receptors suppress transmitter release through G-protein-coupled inhibition of calcium currents.

Tenascin expression in endomyocardial biopsy specimens in patients with dilated cardiomyopathy: distribution along margin of fibrotic lesions.

OBJECTIVE: To examine the hypothesis that tenascin, an extracellular matrix glycoprotein, contributes to fibrotic changes in dilated cardiomyopathy. METHODS: The localisation of tenascin in biopsy specimens of the hearts obtained from eight patients with dilated cardiomyopathy was examined using staining by the avidin-biotin-peroxidase complex method. RESULTS: (1) Perimysium and endomysium. Although positive staining for tenascin was observed in the enlarged perimysium and endomysium in all patients, moderately intense staining was characteristically observed near the replacement fibrotic lesions. In the narrow perimysium and endomysium of the myocardium not containing replacement fibrotic lesions, tenascin was not present, as in the control specimens. (2) Replacement fibrotic lesions. Non-homogeneous positive staining for tenascin was detected in all replacement fibrotic lesions examined. Intense tenascin deposition was observed in the peripheral portion of the replacement fibrotic lesions. The tenascin staining observed in the small replacement fibrotic lesions was more intense than that in the large lesions. CONCLUSIONS: Tenascin contributes to the development of the fibrotic changes seen in the dilated cardiomyopathic heart. Its characteristic location, specifically the distribution along the margin of the fibrosis, suggests that fibrotic change is a continuous process in hearts with dilated cardiomyopathy.

Sequential changes in the distribution of type I and III collagens in the infarct zone: immunohistochemical study of experimental myocardial infarction in the rat.

AIM: Ventricular remodeling following acute myocardial infarction is an important factor in prognosis. The healing process, involving changes in type I and III collagens, is one of the major factors in remodelling. We therefore examined sequential changes in type I and III collagens after experimental myocardial infarction. MATERIALS AND METHODS: Hearts were excised from 1 day to 10 weeks after permanent left coronary ligation in rats. Immunohistochemical staining with a polyclonal antibody to each collagen was performed by the avidin-biotin-peroxidase method. RESULTS: Type I collagen initially appeared in the peripheral zone of the infarct from 3 days after ligation, the extent of staining gradually increasing until it reached a maximal level on days 21-28, after which the distribution remained unchanged. Type III collagen appeared in the peripheral zone of the infarct from 3 days after ligation; the extent of staining reached the maximal level after 11-28 days, after which a slight decrease in the distribution was observed, although the staining did not entirely disappear. CONCLUSIONS: Type I collagen was a major factor in collagen matrix formation, especially in the relatively late phase. Type III collagen, however, contributed particularly to collagen matrix formation in the relatively early phase. This study improves current understanding of the time-dependent alterations in type I and III collagens involved in the healing process after coronary artery occlusion.

Effects of emergency coronary angioplasty on left ventricular volume after acute myocardial infarction compared with intracoronary thrombolysis.

BACKGROUND: The effects of emergency coronary angioplasty on left ventricular remodeling have not been fully evaluated. We compared the effects of emergency coronary angioplasty on left ventricular volume with those of intracoronary thrombolysis in patients suffering from their first acute myocardial infarction (AMI). METHODS: A total of 51 patients who had a culprit lesion at site No 6 of the American Heart Association (AHA) classification were analyzed. Patients with re-obstruction of the culprit lesion after reperfusion were excluded from the study. The coronary angioplasty and the thrombolysis groups consisted of 28 and 23 patients, respectively. Left ventricular volume was measured by left ventriculography at 4 weeks after infarction. RESULTS: Clinical and angiographic background factors showed no significant differences between these two groups. The left ventricular end-systolic volume index was significantly smaller in the angioplasty group than in the thrombolysis group (31 +/- 14 versus 45 +/- 14 ml/m2, P < 0.01). Similarly, the left ventricular end-diastolic volume index was significantly smaller in the angioplasty group (64 +/- 13 versus 82 +/- 13 ml/m2, P < 0.01). Conversely, the left ventricular ejection fraction was larger in the angioplasty group than in the thrombolysis group (54 +/- 13 versus 45 +/- 13%, P < 0.05). Multivariate analysis revealed that the selection of coronary angioplasty was one of the factors significantly associated with a decrease in left ventricular end-systolic and end-diastolic volume. CONCLUSION: These results suggest that emergency coronary angioplasty produces better left ventricular remodeling than intracoronary thrombolysis after AMI.

NG-nitro-L-arginine attenuates flow debt repayment in the reactive hyperemic response of the open-chest dog coronary artery: contribution of endothelium-derived relaxing factor.

To test the hypothesis that the endothelium-derived relaxing factor (EDRF) contributes to coronary vasodilation induced by myocardial ischemia, we examined the effect of NG-nitro-L-arginine (a potent and selective inhibitor of EDRF release) on the coronary reactive hyperemic response in the open-chest dogs. Intracoronary infusion of NG-nitro-L-arginine at a coronary plasma concentration of 5 x 10(-5) M had no effect on hemodynamics and myocardial oxygen metabolism, but attenuated repayment of the flow debt by an average of 20.4% and 20.0% following coronary occlusion for 10 sec and 20 sec, respectively. Concomitant infusion of NG-nitro-L-arginine at the same concentration and 8-phenyltheophylline (a potent adenosine receptor blocker) at a coronary plasma concentration of 10(-5) M further attenuated flow debt repayment following 10 sec and 20 sec of coronary occlusion by 47.7 and 59.4%, respectively. These results indicate that EDRF plays a significant role in the coronary reactive hyperemic response and may cause vasodilation independently of adenosine-mediated vasodilation following coronary occlusion.

Factors affecting the perception of low-level vibration.

The level at which vibration becomes a nuisance is low, well below the vibration intensity discussed with regard to the health of industrial workers in the International Standard ISO-2631 draft. The relationships between the various factors and the human response to low-level vibration generated by vehicular traffic, are discussed from the results obtained from questionnaires. A female may respond to a lower level than male. There is no difference in response to low-level vibration between standing and sitting postures. Accompanying noise distracts the perception of low-level vibration, however at high levels, the effect of distraction is reduced.

Changes in soft tissue profile after surgical correction of skeletal class III malocclusion.

Cephalometric analysis of the facial soft tissue profile after surgical correction of skeletal Class III malocclusion performed either in the ascending ramus or in the mandibular body in 33 patients showed a close correlation between the horizontal movements of the soft tissue landmarks and those of the underlying skeletal and dental structures. In the vertical direction, the changes were more variable. A comparison of these results with the soft tissue profile of normal persons indicated that a natural appearance could be achieved after correction of Class III malocclusion by combined surgery and orthodontic treatment.

Stability of the mandible after surgical correction of skeletal class III malocclusion in 50 patients.

Fifty cases of skeletal Class III malocclusion were analyzed by the tracings of presurgical and postsurgical cephalograms to evaluate the stability of the mandible a year after surgery. In 33 patients, the curved oblique osteotomy in the ascending ramus was used; the correction was made in the mandibular body for 17 patients by either the rectangular osteotomy or the sliding osteotomy. Minimal relapse was observed in all three procedures, with the least amount occurring after mandibular body ostectomy or osteotomy. The results were considered to be due to careful determination of the correct time for surgery in each patient to avoid skeletal relapse resulting in continued mandibular growth, prompt osseous healing at the surgical sites by providing close and tight bony contact between the segments, elimination of the effect of the major muscles of mastication, minimum alteration in the position of the posterior segment and trimming of the margin of the anterior segment to form a proper gonial angle, and a stable occlusion with maximum intercuspation and an adequate overbite. In addition, preoperative orthodontic treatment and extraoral traction of the mandible by chin cups were considered effective means to stabilize the post-operative occlusion.

Surgical-orthodontic approach to skeletal class III malocclusion. Analysis of 45 cases with evaluation of curved oblique osteotomy and sliding osteotomy.

A curved oblique osteotomy in which the ascending ramus was cut obliquely on a curved line from its anterior border to the angle was used for the treatment of 29 patients with skeletal Class III malocclusion, and 16 other patients were corrected by either an ordinary body ostectomy or a sliding osteotomy in the first premolar region. Both curved oblique osteotomy and sliding osteotomy could easily be performed with a Stryker's reciprocating saw, and osseous healing at the sites of surgery was rapid as a large area of intimate bony contact between the segments was obtained. The resulting profile and skeletal changes studied by cephalograms were excellent, with no significant relapse, and recovery of a stable occlusion was attained. The combined approach with orthodontists which included thorough analysis of each patient, preoperative alignment of the dental arches and postoperative care was essential for obtaining the best results.