Store-operated Ca entry (SOCE) is a Ca-entry process activated by the depletion of intracellular stores and has an important role in many cell types. In skeletal muscle, however, its role during physiological muscle activation has been controversial. To address this question, sarcoplasmic reticulum (SR) calcium release in a mouse strain with a naturally occurring mutation in the myostatin gene (Compact (Cmpt)) leading to a hypermuscular yet reduced muscle-force phenotype was compared to that in wild-type mice. To elicit Ca release from the SR of flexor digitorum brevis (FDB) fibers, either a ryanodine receptor agonist (4-chloro-meta-cresol) or depolarizing pulses were used. In muscles from Cmpt mice, endogenous protein levels of STIM1 and Orai1 were reduced, and consequently, SOCE after 4-chloro-meta-cresol-induced store depletion was suppressed. Although the voltage dependence of SR calcium release was not statistically different between wild-type and Cmpt fibers, the amount of releasable calcium was significantly reduced in the latter, indicating a smaller SR content. To assess the immediate role of SOCE in replenishing the SR calcium store, the evolution of intracellular calcium concentration during a train of long-lasting depolarizations to a maximally activating voltage was monitored. Cmpt mice exhibited a faster decline in calcium release, suggesting a compromised ability to refill the SR. A simple model that incorporates a reduced SOCE as an important partner in regulating immediate calcium influx through the surface membrane readily accounts for the steady-state reduction in SR calcium content and its more pronounced decline after calcium release.

Mitochondria play key roles in cellular energy generation and lifespan of most eukaryotes. To understand the functions of four nuclear-encoded genes predicted to be related to the maintenance of mitochondrial morphology and function in Aspergillus nidulans, systematic characterization was carried out. The deletion and overexpression mutants of aodA, dnmA, mnSOD and pimA encoding alternative oxidase, dynamin related protein, manganese superoxide dismutase and Lon protease, respectively, were generated and examined for their growth, stress tolerances, respiration, autolysis, cell death, sterigmatocystin production, hyphal morphology and size, and mitochondrial superoxide production as well as development. Overall, genetic manipulation of these genes had less effect on cellular physiology and ageing in A. nidulans than that of their homologs in another fungus Podospora anserina with a well-characterized senescence. The observed interspecial phenotypic differences can be explained by the dissimilar intrinsic stabilities of the mitochondrial genomes in A. nidulans and P. anserina. Furthermore, the marginally altered phenotypes observed in A. nidulans mutants indicate the presence of effective compensatory mechanisms for the complex networks of mitochondrial defense and quality control. Importantly, these findings can be useful for developing novel platforms for heterologous protein production, or on new biocontrol and bioremediation technologies based on Aspergillus species.

The pedunculopontine nucleus (PPN) is known as the cholinergic part of the reticular activating system (RAS) and it plays an important role in transitions of slow-wave sleep to REM sleep and wakefulness. Although both exogenous and endocannabinoids affect sleep, the mechanism of endocannabinoid neuromodulation has not been characterized at cellular level in the PPN. In this paper, we demonstrate that both neurons and glial cells from the PPN respond to cannabinoid type 1 (CB1) receptor agonists. The neuronal response can be depolarization or hyperpolarization, while astrocytes exhibit more frequent calcium waves. All these effects are absent in CB1 gene-deficient mice. Blockade of the fast synaptic neurotransmission or neuronal action potential firing does not change the effect on the neuronal membrane potential significantly, while inhibition of astrocytic calcium waves by thapsigargin diminishes the response. Inhibition of group I metabotropic glutamate receptors (mGluRs) abolishes hyperpolarization, whereas blockade of group II mGluRs prevents depolarization. Initially active neurons and glial cells display weaker responses partially due to the increased endocannabinoid tone in their environment. Taken together, we propose that cannabinoid receptor stimulation modulates PPN neuronal activity in the following manner: active neurons may elicit calcium waves in astrocytes via endogenous CB1 receptor agonists. Astrocytes in turn release glutamate that activates different metabotropic glutamate receptors of neurons and modulate PPN neuronal activity.

Oláh et al. Western-blot analysis of TRPC1 in the transfected clones. The 87 kDa human isoform

Marijuana was found to cause muscle weakness, although it is unknown whether it affects the muscles directly or modulates only the motor control of the central nervous system. Although the presence of CB1 cannabinoid receptors (CB1R), which are responsible for the psychoactive effects of the drug in the brain, have recently been demonstrated in skeletal muscle, it is unclear how CB1R-mediated signalling affects the contraction and Ca²⁺ homeostasis of mammalian skeletal muscle. In the present study, we demonstrate that in vitro CB1R activation increased muscle fatigability and decreased the Ca -sensitivity of the contractile apparatus, whereas it did not alter the amplitude of single twitch contractions. In myotubes, CB1R agonists neither evoked, nor influenced inositol 1,4,5-trisphosphate (IP )-mediated Ca transients, nor did they alter excitation-contraction coupling. By contrast, in isolated muscle fibres of wild-type mice, although CB1R agonists did not evoke IP -mediated Ca transients too, they significantly reduced the amplitude of the depolarization-evoked transients in a pertussis-toxin sensitive manner, indicating a G protein-dependent mechanism. Concurrently, on skeletal muscle fibres isolated from CB1R-knockout animals, depolarization-evoked Ca transients, as well qas Ca release flux via ryanodine receptors (RyRs), and the total amount of released Ca was significantly greater than that from wild-type mice. Our results show that CB1R-mediated signalling exerts both a constitutive and an agonist-mediated inhibition on the Ca transients via RyR, regulates the activity of the sarcoplasmic reticulum Ca ATPase and enhances muscle fatigability, which might decrease exercise performance, thus playing a role in myopathies, and therefore should be considered during the development of new cannabinoid drugs.