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The architecture of mitochondria adapts to physiological contexts: while mitochondrial fragmentation is usually associated to quality control and cell death, mitochondrial elongation often enhances cell survival during stress. Understanding how these events are regulated is important to elucidate how mitochondrial dynamics control cell fate. Here, we show that the tyrosine kinase Src regulates mitochondrial morphology. Deletion of Src increased mitochondrial size and reduced cellular respiration independently of mitochondrial mass, mitochondrial membrane potential or ATP levels. Re-expression of Src targeted to the mitochondrial matrix, but not of Src targeted to the plasma membrane, rescued mitochondrial morphology in a kinase activity-dependent manner. These findings highlight a novel function for Src in the control of mitochondrial dynamics. [ABSTRACT FROM AUTHOR]

Research on isometric contractions in subjects with Parkinson’s disease (PD) has shown that anti-parkinsonian medication results in a greater increase in extensor strength than flexor strength. This finding is consistent with the hypothesis that there is a greater impairment in neural activation of extensor muscles as compared to flexor muscles in subjects with PD. Such a hypothesis is physiologically feasible given the known differences in the neural control of flexor and extensor muscles. If the above hypothesis is true for both phasic and tonic muscle activation, then differences between performance of rapid single-joint flexion and extension movements should exist in subjects with PD. Twelve subjects with PD, “off” and “on” medication, and 12 age- and sex-matched healthy control subjects performed rapid single-joint movements in flexion and extension over three distances. For neurologically healthy subjects, we did not identify any significant differences in either kinematic or EMG parameters between flexion and extension movements. In contrast, in the PD subjects extension movements were slower and associated with more agonist bursts when compared to flexion movements. The results are consistent with the hypothesis that there is a differential impairment of neural activation of extensor muscles of the arm as compared to flexor muscles in subjects with PD. [ABSTRACT FROM AUTHOR]

Movements have been described as being governed by a speed-sensitive (SS) or speed-insensitive (SI) strategy. The SS strategy is used when the subject controls, either explicitly or implicitly, movement speed or time. In contrast, the SI strategy is utilized when there is no intention or requirement to control movement speed. The different strategies demonstrate a specific relationship between torque trajectories and muscle activity. The purpose of this study was to determine the effect of accuracy and force level on strategy selection. Ten healthy adults were instructed to generate isometric pulse contractions of the right soleus at 20%, 40%, and 60% of maximum voluntary contraction (MVC) to reach five target sizes of percentage MVC (4%, 8%, 12%, 16%, 20%). The following results were observed: (1) there was no difference in time to peak force, peak d F/d t, slope of force, and electromyographic (EMG) measures between the 12%, 16%, and 20% target sizes; (2) differences were noted, however, between the 12%, 16%, and 20% targets and the smaller targets; (3) for the dependent measures there were significant differences between each force level. No difference between the larger targets implies that subjects do not need to implement a strategy and suggests an upper limit to the dual-strategy hypothesis. The difference between the smaller and larger targets and the difference between the force levels is indicative of an SS strategy. When asked to use different force levels, subjects controlled the rate of rise of force and regulated time to peak force. Between target sizes, force and time were modulated equally. [ABSTRACT FROM AUTHOR]