Gq-coupled receptors as mechanosensors mediating myogenic vasoconstriction

Despite the central physiological function of the myogenic response, the underlying signalling pathways and the identity of mechanosensors in vascular smooth muscle (VSM) are still elusive. In contrast to present thinking, we show that membrane stretch does not primarily gate mechanosensitive transient receptor potential (TRP) ion channels, but leads to agonist-independent activation of G(q/11)-coupled receptors, which subsequently signal to TRPC channels in a G protein- and phospholipase C-dependent manner. Mechanically activated receptors adopt an active conformation, allowing for productive G protein coupling and recruitment of beta-arrestin. Agonist-independent receptor activation by mechanical stimuli is blocked by specific antagonists and inverse agonists. Increasing the AT(1) angiotensin II receptor density in mechanically unresponsive rat aortic A7r5 cells resulted in mechanosensitivity. Myogenic tone of cerebral and renal arteries is profoundly diminished by the inverse angiotensin II AT(1) receptor agonist losartan independently of angiotensin II (AII) secretion. This inhibitory effect is enhanced in blood vessels of mice deficient in the regulator of G-protein signalling-2. These findings suggest that G(q/11)-coupled receptors function as sensors of membrane stretch in VSM cells.     

Mechanisms of ADRF release from rat aortic adventitial adipose tissue

Blood vessels are surrounded by variable amounts of adipose tissue. We showed earlier that adventitial adipose tissue inhibits rat aortic contraction by release of a transferable factor, adventitium-derived relaxing factor (ADRF), which activates smooth muscle K(+) channels. However, little is known about the mechanisms of ADRF release. Using isolated rat aortic rings and isometric contraction measurements, we show that ADRF release depends on extracellular [Ca(2+)] (EC(50) approximately 4.7 mM). ADRF effects do not involve neuronal presynaptic N-type Ca(2+) and Na(+) channels or vanilloid, cannabinoid, and CGRP receptors. ADRF release is strongly inhibited by the protein tyrosine kinase inhibitors genistein and tyrphostin A25. In contrast, daidzein, an inactive genistein analog, and the protein tyrosine kinase inhibitor ST638 had no effect. Protein kinase A inhibition by H89 also inhibited ADRF release, whereas the protein kinase G inhibitor KT-5823 had no effect. We propose that ADRF release is Ca(2+) dependent and is regulated by intracellular signaling pathways involving tyrosine kinase and protein kinase A. Furthermore, ADRF release does not depend on perivascular nerve endings.     

Sildenafil,N-desmethyl-sildenafil and Zaprinast enhance photoreceptor response in the isolated rat retina

Here we report that the active component of Viagra, Sildenafil and the first metabolite, N-desmethyl-sildenafil (UK-103, 320) increased the amplitude of flash-evoked electroretinogram (ERG) of dark-adapted albino rat retina. Effects of Sildenafil and N-desmethyl-sildenafil were comparable to those of the known phosphodiesterase inhibitor, Zaprinast. The photoreceptor cell response was isolated by blocking the glial K(+) ion-buffering and the on-bipolar components of the ERG with the use of BaCl(2) (500 microM) and the specific type VI metabotropic glutamate receptor agonist, DL-2-amino-4-phosphonobutyric acid (25 microM), respectively. Zaprinast, Sildenafil and N-desmethyl-sildenafil (1 microM each) increased the amplitude of photoreceptor cell response either. Besides, Sildenafil was significantly more effective than N-desmethyl-sildenafil. These findings suggest an increased sensitivity of photoreceptor cells in the presence of Sildenafil and it is metabolite.     

Bioadhesion of supramolecular structures at supported planar bilayers as studied by the quartz crystal microbalance

A quartz crystal microbalance (QCM) was used to study the adhesion behavior of supramolecular aggregates at supported planar bilayers (SPBs). The QCM technique is a suitable method to detect the adsorption of biomolecules at the quartz surface owing to its sensitivity for changes in mass and viscoelastic properties. To simulate biomembranes, the quartz plates were coated with highly ordered lipid films. Therefore, a combination of self-assembled monolayers and Langmuir-Blodgett films was used. Firstly, the adsorption of liposomes coupled with the lectin concanavalin A was investigated at glycolipid-containing model membranes. Using different carbohydrates, it was possible to determine specific and nonspecific parts of the interactions. The adhesion occurred owing to specific lectin-carbohydrate interactions (about 20%) and to nonspecific interactions (about 80%). The composition of the liposomes was changed to simulate the structure of a native biomembrane consisting of the glycocalix, the lipid-protein bilayer, and the cytoskeleton. An artificial glycocalix was created by incorporating poly(ethylene glycol) into the liposomes. Liposomes which were intravesicular polymerized with polyacrylamide or polyacrylcholate simulated the cytoskeleton. It was determined that the modified liposomes had significant lower interactions with SPBs. The adsorption was reduced by approximately 80% compared to unmodified liposomes. Secondly, a model was developed for the detection of interactions between simple or mixed bile salt micelles and model membranes. It was found that simple bile salts did not adsorb at model membranes. Binary systems consisting of bile salt and phospholipid induced only small interactions. On the other hand, ternary systems consisting of bile salt, phospholipid, and fatty acid showed strong interactions. A dependence on the chain length of the fatty acid was observed. Thirdly, the interaction between ganglioside-containing model membranes and cholera toxin (beta-subunit) was investigated. Different ganglioside fractions showed varying adsorption in the following sequence: GM1 > GD1a > GD1b > GT1b.     

Comparative study of lignins isolated from Alfa grass (Stipa tenacissima L.)

Soda lignin, dioxane lignin and milled lignin were isolated from Alfa grass (Stipatenacissima L.). The physico-chemical characterization of three different lignins: one industrial lignin precipitated from soda spent liquor and two lignin preparations isolated under laboratory conditions from Alfa grass (also know as Esparto grass) was performed. The structures of lignins were studied by three non-destructive (FT-IR, solid state ¹³C NMR and UV/visible spectroscopy) and two destructive (nitrobenzene oxidation and thermogravimetric analysis) methods. Elemental analysis and the methoxyl content determination were performed in order to determine the C₉ formulae for the studied lignins. The total antioxidant capacity of the studied lignins has been determined and compared to commercial antioxidants commonly used in thermoplastic industry.     

Evaluation of Multiband EPI Acquisitions for Resting State fMRI

Functional magnetic resonance imaging (fMRI) and particularly resting state fMRI (rs-fMRI) is widely used to investigate resting state brain networks (RSNs) on the systems level. Echo planar imaging (EPI) is the state-of-the-art imaging technique for most fMRI studies. Therefore, improvements of EPI might lead to increased sensitivity for a large amount of studies performed every day. A number of developments to shorten acquisition time have been recently proposed and the multiband technique, allowing the simultaneous acquisition of multiple slices yielding an equivalent reduction of measurement time, is the most promising among them. While the prospect to significantly reduce acquisition time by means of high multiband acceleration factors (M) appears tempting, signal quality parameters and the sensitivity to detect common RSNs with increasing M-factor have only been partially investigated up to now. In this study, we therefore acquired rs-fMRI data from 20 healthy volunteers to systematically investigate signal characteristics and sensitivity for brain network activity in datasets with increasing M-factor, M = 2 − 4. Combined with an inplane, sensitivity encoding (SENSE), acceleration factor, S = 2, we applied a maximal acceleration factor of 8 (S2×M4). Our results suggest that an M-factor of 2 (total acceleration of 4) only causes negligible SNR decrease but reveals common RSN with increased sensitivity and stability. Further M-factor increase produced random artifacts as revealed by signal quality measures that may affect interpretation of RSNs under common scanning conditions. Given appropriate hardware, a mb-EPI sequence with a total acceleration of 4 significantly reduces overall scanning time and clearly increases sensitivity to detect common RSNs. Together, our results suggest mb-EPI at moderate acceleration factors as a novel standard for fMRI that might increase our understanding of network dynamics in healthy and diseased brains.