Ricardo Bull

Patterns of electromyographic activity in subjects with different skeletal facial types

Integrated electromyographic activity of masseter and anterior temporal muscles was recorded using bipolar surface electrodes in 33 young adults. Subjects were skeletally classified according to ANB angle reading corrected both for maxillary position and rotation of the jaw. Postural activity for both muscles was higher in Class III subjects than in Class I and Class II, whereas in Class I and II subjects activity was similar. During swallowing, masseter muscle activity in Class III subjects was higher than Classes I and II, whereas anterior temporal muscle activity was not different between Classes III and I. During maximal voluntary clenching, activity was not different among classes. High correlations between electromyographic activity and corrected ANB angle as well as with overjet were observed. Skeletal classification used in the present study may have clinical relevance regarding treatment and prognosis, as well as in the assessment of the relationship between muscular activity and craniofacial characteristics.

Activation of calcium channels in sarcoplasmic reticulum from frog muscle by nanomolar concentrations of ryanodine.

Sarcoplasmic reticulum vesicles isolated from fast-twitch frog skeletal muscle presented two classes of binding sites for ryanodine, one of high affinity (Kd1 = 1.7 nM, Bmax1 = 3.3 pmol per mg) and a second class with lower affinity (Kd2 = 90 nM, Bmax2 = 7.0 pmol per milligram). The calcium channels present in the sarcoplasmic reticulum membranes were studied in vesicles fused into lipid bilayers. Low concentrations of ryanodine (5 to 10 nM) activated a large conductance calcium channel after a short delay (5 to 10 min). The activation, which could be elicited from conditions of high or low fractional open time, was characterized by an increase in channel fractional open time without a change in conductance. The open and closed dwell time distributions were fitted with the sum of two exponentials in the range of 4 to 800 ms. The activating effect of ryanodine was due to an increase of both open time constants and a concomitant decrease in the closed time constants. Under conditions of low fractional open time (less than 0.1), the time spent in long closed periods (greater than 800 ms) between bursts was not affected by ryanodine. Higher concentrations of ryanodine (250 nM) locked the channel in a lower conductance level (approximately 40%) with a fractional open time near unity. These results suggest that the activating effects of nanomolar concentrations of ryanodine may arise from drug binding to high affinity sites. The expression of the lower conductance state obtained with higher concentrations of ryanodine may be associated with the low affinity binding sites observed in frog sarcoplasmic reticulum.

Sarcoplasmic reticulum release channels from frog skeletal muscle display two types of calcium dependence

Calcium channels derived from sarcoplasmic reticulum of frog skeletal muscle were fused with planar lipid bilayers. Fractional open times displayed two types of calcium dependence: (i) blockable channels showed a bell‐shaped calcium dependence with an activation constant of 4.5 μM, a Hill coefficient for activation of 1.46 and a blocking constant of 226 μM, and (ii) non‐blockable channels displayed a sigmoidal calcium dependence with an activation constant of 1.1 μM and a Hill coefficient of 1.42; no blocking effect was seen with calcium up to 0.5 mM. These two types of calcium dependence may underlie the coexistence of two different pathways for calcium release in frog skeletal muscle.

Ischemia Enhances Activation by Ca2+ and Redox Modification of Ryanodine Receptor Channels from Rat Brain Cortex

Cerebral ischemia stimulates Ca2+ influx and thus increases neuronal intracellular free [Ca2+]. Using a rat model of cerebral ischemia without recirculation, we tested whether ischemia enhances the activation by Ca2+ of ryanodine receptor (RyR) channels, a requisite feature of RyR-mediated Ca2+-induced Ca2+ release (CICR). To this aim, we evaluated how single RyR channels from endoplasmic reticulum vesicles, fused into planar lipid bilayers, responded to cytoplasmic [Ca2+] changes. Endoplasmic reticulum vesicles were isolated from the cortex of rat brains incubated without blood flow for 5 min at 37°C (ischemic) or at 4°C (control). Ischemic brains displayed increased oxidative intracellular conditions, as evidenced by a lower ratio (∼130:1) of reduced/oxidized glutathione than controls (∼200:1). Single RyR channels from ischemic or control brains displayed the same three responses to Ca2+ reported previously, characterized by low, moderate, or high maximal activity. Relative to controls, RyR channels from ischemic brains displayed with increased frequency the high activity response and with lower frequency the low activity response. Both control and ischemic cortical vesicles contained the RyR2 and RyR3 isoforms in a 3:1 proportion, with undetectable amounts of RyR1. Ischemia reduced [3H]ryanodine binding and total RyR protein content by 35%, and increased at least twofold endogenous RyR2 S-nitrosylation and S-glutathionylation without affecting the corresponding RyR3 endogenous levels. In vitro RyR S-glutathionylation but not S-nitrosylation favored the emergence of high activity channels. We propose that ischemia, by enhancing RyR2 S-glutathionylation, allows RyR2 to sustain CICR; the resulting amplification of Ca2+ entry signals may contribute to cortical neuronal death.

Redox regulation of RyR-mediated Ca2+ release in muscle and neurons

Changes in the redox state of the intracellular ryanodine receptor/Ca2+ release channels of skeletal and cardiac muscle or brain cortex neurons affect their activity. In particular, agents that oxidize or alkylate free SH residues of the channel protein strongly enhance Ca(2+)-induced Ca2+ release, whereas reducing agents have the opposite effects. We will discuss here how modifications of highly reactive cysteine residues by endogenous redox agents or cellular redox state influence RyR channel activation by Ca2+ and ATP or inhibition by Mg2+. Possible physiological and pathological implications of these results on cellular Ca2+ signaling will be addressed as well.

Influence of variation in anteroposterior occlusal contacts on electromyographic activity

A full upper stabilization splint divided into three pairs of occlusal bilateral blocks was made for eight healthy young adult subjects. The three pairs of blocks allowed the location of the centric occlusal contacts to vary and to be distributed over equivalent periodontal surfaces. The electromyographic activity of the masseter and temporal muscles was recorded with surface electrodes during maximum voluntary clenching over the centric occlusal blocks. The electromyographic activity from the elevator muscles with the anterior blocks was significantly less than with the intermediate and posterior occlusal blocks. With use of the intermediate blocks, the activity from the elevator muscles was significantly less than with the posterior blocks. The elevator activity with the posterior blocks was similar to that with the full coverage splint.

Influence of the activator on electromyographic activity of mandibular elevator muscles

Integrated electromyographic (IEMG) activity was recorded in 15 children with Class II, Division 1 malocclusion undergoing treatment with an activator. EMG activity was recorded with surface electrodes from anterior temporal and masseter muscles, with and without the activator in the postural mandibular position, during saliva swallowing and maximal voluntary clenching. Similar IEMG activity in the postural mandibular position and during maximal voluntary clenching, with and without activator, was observed. During saliva swallowing, the activity in both muscles was significantly higher with the activator. This supports the rationale for diurnal wear of the activator. Simple linear regression analysis showed a significant negative correlation between the change of masseter muscular activity during saliva swallowing and age of the children (r = -0.51), suggesting that treatment with the activator should be started at an early age.

Influence of balanced occlusion and canine guidance on electromyographic activity of elevator muscles in complete denture wearers

Electromyographic recordings were made from the anterior temporal and masseter muscles during maximal voluntary clenching with complete dentures in the intercuspal position and in the laterotrusive jaw position with balanced occlusion and canine guidance. The different pattern of activity of the two muscles in the laterotrusive occlusal schemes studied suggests that their motoneuron pools receive different inputs. The lower activity in both muscles with canine guidance suggests that canine guidance may be a significant factor for preventing parafunctional activity in edentulous patients.

Age-Dependent Increases in Apoptosis/Necrosis Ratios in Human Lymphocytes Exposed to Oxidative Stress

Unlike apoptosis, mechanisms leading to necrosis are less well understood. Moreover, changes in necrosis as a function of age have not been studied in human lymphocytes. H(2)O(2)-induced death of peripheral lymphocytes (56 healthy donors, 24-95 years) was evaluated by flow cytometry and propidium iodide staining, caspase activation, DNA laddering, and electron microscopy. H(2)O(2)-induced stress was associated with high levels of necrosis in young individuals (≤30 years), whereas progressively enhanced apoptotic death was observed in older donors, without changes in overall lymphocyte survival. Thus, apoptosis/necrosis ratios were inverted in young versus elderly (≥65 years) donors. Death was not accompanied by increased caspase activity and, accordingly, unaffected by caspase inhibition; however, it was almost completely prevented by poly ADP ribose polymerase inhibition. In summary, aging was associated with changes in the apoptosis/necrosis ratios, rather than susceptibility per se to H(2)O(2)-induced death, which was caspase independent but poly ADP ribose polymerase dependent. Understanding this switch in death modes may aid in understanding age-related disorders.

Calcium dependence of ryanodine-sensitive calcium channels from brain cortex endoplasmic reticulum.

Endoplasmic reticulum vesicles isolated from rat brain cortex and fused with lipid bilayers displayed ryanodine‐sensitive calcium channels, with three cytoplasmic calcium dependences. A: Channels (n = 5) stimulated by Ca2+ (K 0.5 = 1.2 μM and n Hill = 1.9) and not inhibited up to 0.5 mM Ca2+. B: Channels (n = 14) cooperatively activated (K 0.5 = 6.9 μM and n Hill = 1.8), and inhibited by Ca2+ (K 0.5 = 152 μM and n Hill = 1.8). C: Low P o (< 0.1) channels (n = 22), non‐cooperatively activated and inhibited with the same K 0.5 = 26.3 μM Ca2+. These three types of responses to cytoplasmic [Ca2+] may underlie separate calcium release pathways in neurons of rat brain cortex.