KCl has long been used as a convenient stimulus to bypass G protein-coupled receptors (GPCR) and activate smooth muscle by a highly reproducible and relatively "simple" mechanism involving activation of voltage-operated Ca2+ channels that leads to increases in cytosolic free Ca2+ ([Ca2+]i), Ca2+-calmodulin-dependent myosin light chain (MLC) kinase activation, MLC phosphorylation and contraction. This KCl-induced stimulus-response coupling mechanism is a standard tool-set used in comparative studies to explore more complex mechanisms generated by activation of GPCRs. One area where this approach has been especially productive is in studies designed to understand Ca2+ sensitization, the relationship between [Ca2+]i and force produced by GPCR agonists. Studies done in the late 1980s demonstrated that a unique relationship between stimulus-induced [Ca2+]i and force does not exist: for a given increase in [Ca2+]i, GPCR activation can produce greater force than KCl, and relaxant agents can produce the opposite effect to cause Ca2+ desensitization. Such changes in Ca2+ sensitivity are now known to involve multiple cell signaling strategies, including translocation of proteins from cytosol to plasma membrane, and activation of enzymes, including RhoA kinase and protein kinase C. However, recent studies show that KCl can also cause Ca2+ sensitization involving translocation and activation of RhoA kinase. Rather than complicating the Ca2+ sensitivity story, this surprising finding is already providing novel insights into mechanisms regulating Ca2+ sensitivity of smooth muscle contraction. KCl as a "simple" stimulus promises to remain a standard tool for smooth muscle cell physiologists, whose focus is to understand mechanisms regulating Ca2+ sensitivity.

KCl causes smooth muscle contraction by elevating intracellular free Ca2+, whereas receptor stimulation activates an additional mechanism, termed Ca2+ sensitization, that can involve activation of RhoA-associated kinase (ROK) and PKC. However, recent studies support the hypothesis that KCl may also increase Ca2+ sensitivity. Our data showed that the PKC inhibitor GF-109203X did not, whereas the ROK inhibitor Y-27632 did, inhibit KCl-induced tonic (5 min) force and myosin light chain (MLC) phosphorylation in rabbit artery. Y-27632 also inhibited BAY K 8644- and ionomycin-induced MLC phosphorylation and force but did not inhibit KCl-induced Ca2+ entry or peak (∼15 s) force. Moreover, KCl and BAY K 8644 nearly doubled the amount of ROK colocalized to caveolae at 30 s, a time that preceded inhibition of force by Y-27632. Colocalization was not inhibited by Y-27632 but was abolished by nifedipine and the calmodulin blocker trifluoperazine. These data support the hypothesis that KCl caused Ca2+ sensitization via ROK activation. We discuss a novel model for ROK activation involving translocation to caveolae that is dependent on Ca2+ entry and involves Ca2+-calmodulin activation.

Identifying the cell types responsible for RANKL production is critical to the development of a strategy to prevent periprosthetic osteolysis.

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Metabolic stress causes an increased Fas-FasL (receptor-ligand pair) expression in Neural Stem Cells (NSCs) leading to Fas-induced apoptosis. In this study, we discuss the exposure of NSCs to different metabolic treatments that provoke cellular stress responses. We demonstrate that challenging cultured NSCs to ethanol (ETOH) increased cellular death via Fas-mediated apoptosis. Moreover, we establish that NSCs cultured under low lipid conditions, in which they were deprived of essential fatty acids, demonstrated increased cellular survival rates suggesting an increased ability for these lipid-starved cells to endure a stressed environment. This was further confirmed by exposing NSCs to low glucose levels and observing a decrease in percent death in low lipid NSCs. When stressed, NSCs have increased reactive oxygen levels and are susceptible to apoptosis. These findings indicate that under starved and stressed conditions, and in the presence of Fas Ligand (FasL), NSCs pursue fatty acid oxidation by burning fat as fuel. This may be the key to better understand the metabolic states of brain tumors and the characteristics of cancer.