Emerging roles of inositol 1,4,5-trisphosphate signaling in cardiac myocytes

Inositol 1,4,5-trisphosphate (IP3) is a ubiquitous intracellular messenger regulating diverse functions in almost all mammalian cell types. It is generated by membrane receptors that couple to phospholipase C (PLC), an enzyme which liberates IP3 from phosphatidylinositol 4,5-bisphosphate (PIP2). The major action of IP3, which is hydrophilic and thus translocates from the membrane into the cytoplasm, is to induce Ca2+ release from endogenous stores through IP3 receptors (IP3Rs). Cardiac excitation-contraction coupling relies largely on ryanodine receptor (RyR)-induced Ca2+ release from the sarcoplasmic reticulum. Myocytes express a significantly larger number of RyRs compared to IP3Rs (~100:1), and furthermore they experience substantial fluxes of Ca2+ with each heartbeat. Therefore, the role of IP3 and IP3-mediated Ca2+ signaling in cardiac myocytes has long been enigmatic. Recent evidence, however, indicates that despite their paucity cardiac IP3Rs may play crucial roles in regulating diverse cardiac functions. Strategic localization of IP3Rs in cytoplasmic compartments and the nucleus enables them to participate in subsarcolemmal, bulk cytoplasmic and nuclear Ca2+ signaling in embryonic stem cell-derived and neonatal cardiomyocytes, and in adult cardiac myocytes from the atria and ventricles. Intriguingly, expression of both IP3Rs and membrane receptors that couple to PLC/IP3 signaling is altered in cardiac disease such as atrial fibrillation or heart failure, suggesting the involvement of IP3 signaling in the pathology of these diseases. Thus, IP3 exerts important physiological and pathological functions in the heart, ranging from the regulation of pacemaking, excitation-contraction and excitation-transcription coupling to the initiation and/or progression of arrhythmias, hypertrophy and heart failure

One-step extraction and concentration of estrogens for an adequate monitoring of wastewater using ionic-liquid-based aqueous biphasic systems

Ethinylestradiol (EE2) is a synthetic hormone that has been recognized as one of the most prominent endocrine disruptors found in the aqueous environment. Nevertheless, the low content of EE2 in wastewater makes its identification/quantification unfeasible - a major drawback for the evaluation of its persistence and environmental impact. In this context, a novel extraction/concentration method for EE2 from wastewater is proposed here based on aqueous biphasic systems composed of ionic liquids (ILs). Aqueous biphasic systems formed by several hydrophilic ILs and KNaC4H4O6 were initially screened and optimized, with extraction efficiencies of EE2 for the IL-rich phase ranging between 92 and 100%. Remarkable results were obtained with systems that allow the complete extraction of EE2 in a single-step, and without loss of EE2 or the saturation of the extractive phase. Further, the concentration factors of EE2 attainable with these systems were investigated by a suitable manipulation of the composition of the phase-forming components and the corresponding volumes of the coexisting phases. An outstanding concentration of EE2 up to 1000-fold (from ng L-1 to mu g L-1) in a single extraction and concentration step was achieved for the first time with IL-based aqueous biphasic systems. These systems are straightforwardly envisaged for the monitoring of wastewater as one-step extraction and concentration routes for a wide array of endocrine disrupting chemicals while allowing an adequate evaluation of their environmental impact

Binding and direct activation of the epithelial Na+ channel (ENaC) by phosphatidylinositides

Several distinct types of ion channels bind and directly respond to phosphatidylinositides, including phosphatidylinositol (3,4,5)-trisphosphate (PI(3,4,5)P3) and phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2). This regulation is physiologically relevant for its dysfunction, in some instances, causes disease. Recent studies identify the epithelial Na+ channel (ENaC) as a channel sensitive to phosphatidylinositides. ENaC appears capable of binding both PI(4,5)P2 and PI(3,4,5)P3 with binding stabilizing channel gating. The binding sites for these molecules within ENaC are likely to be distinct with the former phosphoinositide interacting with elements in the cytosolic NH2-terminus of the β- and γ-ENaC subunits and the latter with cytosolic regions immediately following the second transmembrane domains in these two subunits. PI(4,5)P2 binding to ENaC appears saturated at rest and necessary for channel gating. Thus, decreases in cellular PI(4,5)P2 levels may serve as a convergence point for inhibitory regulation of ENaC by G-protein coupled receptors and receptor tyrosine kinases. In contrast, apparent PI(3,4,5)P3 binding to ENaC is not saturated. This enables the channel to respond with gating changes in a rapid and dynamic manner to signalling input that influences cellular PI(3,4,5)P3 levels