Deliu E, Tica AA, Motoc D, Brailoiu GC, Brailoiu E. Intracellular angiotensin II activates rat myometrium. Am J Physiol Cell Physiol 301: C559 -C565, 2011. First published May 22, 2011; doi:10.1152/ajpcell.00123.2011.-Angiotensin II is a modulator of myometrial activity; both AT1 and AT2 receptors are expressed in myometrium. Since in other tissues angiotensin II has been reported to activate intracellular receptors, we assessed the effects of intracellular administration of angiotensin II via microinjection on myometrium, using calcium imaging. Intracellular injection of angiotensin II increased cytosolic Ca 2ϩ concentration ([Ca 2ϩ ]i) in myometrial cells in a dose-dependent manner. The effect was abolished by the AT 1 receptor antagonist losartan but not by the AT2 receptor antagonist PD-123319. Disruption of the endo-lysosomal system, but not that of Golgi apparatus, prevented the angiotensin II-induced increase in [Ca 2ϩ ]i. Blockade of AT1 receptor internalization had no effect, whereas blockade of microautophagy abolished the increase in [Ca 2ϩ ]i produced by intracellular injection of angiotensin II; this indicates that microautophagy is a critical step in transporting the peptide into the endo-lysosomes lumenum. The response to angiotensin II was slightly reduced in Ca 2ϩ -free saline, indicating a major involvement of Ca 2ϩ release from internal stores. Blockade of inositol 1,4,5-trisphosphate (IP 3) receptors with heparin and xestospongin C or inhibition of phospholipase C (PLC) with U-73122 abolished the response to angiotensin II, supporting the involvement of PLC-IP 3 pathway. Angiotensin II-induced increase in [Ca 2ϩ ]i was slightly reduced by antagonism of ryanodine receptors. Taken together, our results indicate for the first time that in myometrial cells, intracellular angiotensin II activates AT 1-like receptors on lysosomes and activates PLC-IP 3-dependent Ca 2ϩ release from endoplasmic reticulum; the response is further augmented by a Ca 2ϩ -induced Ca 2ϩ release mechanism via ryanodine receptors activation. calcium imaging; cytosolic calcium concentration; endoplasmic reticulum; microinjection ANGIOTENSIN II is an eight amino acid peptide that exerts its actions by activation of G protein-coupled receptors, namely AT 1 and AT 2 receptors. Increasing evidence suggests that angiotensin II acts not only as an endocrine/paracrine factor, but also as an autacoid or intracrine peptide, with the ability to signal from within the cell, without stimulating plasma membrane receptors (21, 38). We previously reported that intracellular administration of angiotensin II via liposomes increases contractility of rat aorta via activation of intracellular receptors (7). Similarly, microinjection of angiotensin II increases cytosolic Ca 2ϩ concentration ([Ca 2ϩ ] i ) in vascular smooth muscle cells (13, 16) or kidney proximal tubule cells (49). The intracellular angiotensin II can result either via uptake from the interstitium or by intracellular synthesis. In the latter case, intracellular renin conver...
The objective of this study was to investigate the thermal expansivities and degradation properties for several in vitro conditioned biodegradable poly (lactic acid)/hydroxyapatite (PLA/HA) and poly (lactic acid)/β-tricalcium phosphate (PLA/βTCP) composites with different wt.% of the particle reinforcements (i.e. 10, 20 and 30). The samples were prepared by extrusion followed by injection moulding and incubated in a customized simulated body fluid at 37°C over 60, 90, 120, 150 and 180 days, respectively. Thermal expansion and degradation properties of in vitro conditioned samples, along with dynamic mechanical properties of unconditioned ones were systematically investigated through coefficients of linear thermal expansion (CLTE) and thermal strain changes, decomposition temperatures, weight changes and percent residues. The results indicated that PLA/βTCP composites performed better than PLA/HA composites, irrespective of their filler wt.%, revealing high values of glass transition temperatures, around a mean value of 65 °C, both on dynamic-mechanical analysis (DMA) and dilatation (DIL) measurements but lower values on their degradation temperatures, such as 360 °C. The results suggest the feasibility of tailoring high loaded osteoconductive fillers reinforced PLA composites for various medical and engineering applications.
This study evaluates the effect of CaCO3 fillers extracted from waste eggshells on 3D-printed PLA performance. Samples of neat PLA and PLA reinforced with CaCO3 fillers embedded with different wt.% were prepared using an FDM (fused deposition modeling) technology. The samples were examined using mechanical, dynamic mechanical, thermal, and thermal decomposition analyses. The results revealed increasing elastic moduli, tensile strength, and flexure as the filler content increased. The rheological results from the MFR tests showed that the filler content did not influence the PLA-based samples’ processability. Further, the thermal degradation of neat and various CaCO3-wt.%-reinforced PLA specimens revealed relatively small discrepancies in their exposure to the temperature increase, mainly concerning the eggshell organic components and volatile components, from their processability up to 300 °C. By contrast, the increased filler content positively shifted the peaks along the temperature scale at the maximum degradation rate. Additionally, the weight content of the natural reinforcement strongly influenced the surface wettability and appearance of the samples. Further, the SEM analysis featured both the presence of interlayer disturbances and the interfacial compatibility the PLA with the selected fillers.
This contribution focuses on the development of flax and flax/basalt hybrid reinforced composites based on epoxidized linseed oil (ELO) resin, exploiting the feasibility of different ratios of glutaric anhydride (GA) to maleinized linseed oil (MLO) in the hardener system (50:0, 40:10 and 30:20 wt.%) to provide crosslinked thermosets with balanced properties. The hybrid laminates have been manufactured by resin transfer molding (RTM) and subjected to dynamic–mechanical (DMA) and thermal gravimetry (TGA) analysis. The presence of glutaric anhydride (GA) resulted in hard and relatively brittle flax and flax/basalt laminates, whose loss moduli decreased as the number of basalt plies diminished. Furthermore, the increase in MLO content in the GA:MLO hardener system shifted the glass transition temperatures (Tg) from 70 °C to 59 and 56 °C, which is representative of a decrease in brittleness of the crosslinked resin. All samples exhibited two stages of their decomposition process irrespective of the MLO content. The latter influenced the residual mass content that increased with the increase of the MLO wt.% from 10 to 30 wt.%, with shifts of the final degradation temperatures from 410 °C to 425 °C and 445 °C, respectively.
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