Chondrogenesis is known to be regulated by calcium-dependent signalling pathways in which temporal aspects of calcium homeostasis are of key importance. We aimed to better characterise calcium influx and release functions with respect to rapid calcium oscillations in cells of chondrifying chicken high density cultures. We found that differentiating chondrocytes express the ␣ 1 subunit of voltage-operated calcium channels (VOCCs) at both mRNA and protein levels, and that these ion channels play important roles in generating Ca 2+ influx for oscillations as nifedipine interfered with repetitive calcium transients. Furthermore, VOCC blockade abrogated chondrogenesis and almost completely blocked cell proliferation. The contribution of internal Ca 2+ stores via store-operated Ca 2+ entry (SOCE) seems to be indispensable to both Ca 2+ oscillations and chondrogenesis. Moreover, this is the first study to show the functional expression of STIM1/STIM2 and Orai1, molecules that orchestrate SOCE, in chondrogenic cells. Inhibition of SOCE combined with ER calcium store depletion abolished differentiation and severely diminished proliferation, suggesting the important role of internal pools in calcium homeostasis of differentiating chondrocytes. Finally, we present an integrated model for the regulation of calcium oscillations of differentiating chondrocytes that may have important implications for studies of chondrogenesis induced in various stem cell populations.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Abstract. The long-term relationship between major climatic change, vegetation change, and soil development is complex and poorly understood. In northeastern Hungary, for example, geochemical and pollen studies from a lake sedimentary sequence indicate that in the early postglacial, vegetation changed from a coniferous to deciduous forest, and soils from a podzol to brown earth. But which changed first? Did climatic warming result in a transformation from one soil type to another, which in turn resulted in a change in forest composition, or did the vegetation change first and subsequently alter the soil? How long did these soil transformation processes take? And what mechanisms were involved in the development of a brown-earth soil from a podzol? This paper presents the results of a study addressing some of these questions using palaeoecological analyses of a sedimentary sequence from lake Kis-Mohos To in northeastern Hungary. A proposed model for the process by which a podzol becomes transformed into a brown earth is presented, and possible triggering mechanisms are discussed. Results suggest that in northeastern Hungary the postglacial increase in deciduous populations was not consequent on soil type; rather, deciduous trees increased on podzolic soils, and this increase was one of the triggering mechanisms responsible for the development of brown-earth soils.

Osteoarthritis (OA) is the most common form of chronic musculoskeletal disorders. A migratory stem cell population termed chondrogenic progenitor cells (CPC) with in vitro chondrogenic potential was previously isolated from OA cartilage. Since intracellular Ca 2+ signalling is an important regulator of chondrogenesis, we aimed to provide a detailed understanding of the Ca 2+ homeostasis of CPCs. In this work, CPCs immortalised by lentiviral administration of the human telomerase reverse transcriptase (hTERT) and grown in monolayer cultures were studied. Expressions of all three IP3Rs were confirmed, but no RyR subtypes were detected. Ca 2+ oscillations observed in CPCs were predominantly dependent on Ca 2+ release and store replenishment via store-operated Ca 2+ entry; CPCs express both STIM1 and Orai1 proteins. Expressions of adenosine receptor mRNAs were verified, and adenosine elicited Ca 2+ transients. Various P2 receptor subtypes were identified; P2Y1 can bind ADP; P2Y4 is targeted by UTP; and ATP may evoke Ca 2+ transients via detected P2X subtypes, as well as P2Y1 and P2Y2. Enzymatic breakdown of extracellular nucleotides by apyrase completely abrogated Ca 2+ oscillations, suggesting that an autocrine/paracrine purinergic mechanism may drive Ca 2+ oscillations in these cells.As CPCs possess a broad spectrum of functional molecular elements of Ca 2+ signalling, Ca 2+ -dependent regulatory mechanisms can be supposed to influence their differentiation potential.

TASK-3 (KCNK9 or K2P9.1) channels are thought to promote proliferation and/or survival of malignantly transformed cells, most likely by increasing their hypoxia tolerance. Based on our previous results that suggested mitochondrial expression of TASK-3 channels, we hypothesized that TASK-3 channels have roles in maintaining mitochondrial activity. In the present work we studied the effect of reduced TASK-3 expression on the mitochondrial function and survival of WM35 and A2058 melanoma cells. TASK-3 knockdown cells had depolarized mitochondrial membrane potential and contained a reduced amount of mitochondrial DNA. Compared to their scrambled shRNA-transfected counterparts, they demonstrated diminished responsiveness to the application of the mitochondrial uncoupler [(3-chlorophenyl)hydrazono]malononitrile (CCCP). These observations indicate impaired mitochondrial function. Further, TASK-3 knockdown cells presented reduced viability, decreased total DNA content, altered cell morphology, and reduced surface area. In contrast to non- and scrambled shRNA-transfected melanoma cell lines, which did not present noteworthy apoptotic activity, almost 50 % of the TASK-3 knockdown cells exhibited strong Annexin-V-specific immunofluorescence signal. Sequestration of cytochrome c from the mitochondria to the cytosol, increased caspase 3 activity, and translocation of the apoptosis-inducing factor from mitochondria to cell nuclei were also demonstrated in TASK-3 knockdown cells. Interference with TASK-3 channel expression, therefore, induces caspase-dependent and -independent apoptosis of melanoma cells, most likely via causing mitochondrial depolarization. Consequently, TASK-3 channels may be legitimate targets of future melanoma therapies.

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.