Calcium and protons affect the interaction of neurotransmitters and anesthetics with anionic lipid membranes.

We study how zwitterionic and anionic biomembrane models interact with neurotransmitters (NTs) and anesthetics (ATs) in the presence of Ca(2+) and different pH conditions. As NTs we used acetylcholine (ACh), γ-aminobutyric acid (GABA), and l-glutamic acid (LGlu). As ATs, tetracaine (TC), and pentobarbital (PB) were employed. By using differential scanning calorimetry (DSC), we analyzed the changes such molecules produce in the thermal properties of the membranes. We found that calcium and pH play important roles in the interactions of NTs and ATs with the anionic lipid membranes. Changes in pH promote deprotonation of the phosphate groups in anionic phospholipids inducing electrostatic interactions between them and NTs; but if Ca(2+) ions are in the system, these act as bridges. Such interactions impact the physical properties of the membranes in a similar manner that anesthetics do. Beyond the usual biochemical approach, we claim that these effects should be taken into account to understand the excitatory-inhibitory orchestrated balance in the nervous system.

Biophysical investigation of liposome systems decorated with bioconjugated copolymers in the presence of amantadine.

Liposome-based technologies derived from lipids and polymers (e.g., PEGylated liposomes) have been recognized because of their applications in nanomedicine. However, since such systems represent myriad challenges and may promote immune responses, investigation of new biomaterials is mandatory. Here, we report on a biophysical investigation of liposomes decorated with bioconjugated copolymers in the presence (or absence) of amantadine (an antiviral medication). First, copolymers of poly(N,N-dimethylacrylamide-co-fluoresceinacrylate-co-acrylic acid-N-succinimide ester)-block-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) containing a fluorescence label were biofunctionalized with short peptides that resemble the sequence of the loops 220 and 130 of the binding receptor of the hemagglutinin (HA) protein of the influenza A virus. Then, the bioconjugated copolymers were self-assembled along with liposomes composed of 1,2 dimyristoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol (MSC). These biohybrid systems, with and without amantadine, were systematically characterized using differential scanning calorimetry (DSC), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryoTEM). Finally, the systems were tested in an in vitro study to evaluate cytotoxicity and direct immunofluorescence in Madin Darbin Canine Kidney (MDCK) cells. The biohybrid systems displayed long-term stability, thermo-responsiveness, hydrophilic-hydrophobic features, and fluorescence properties and were presumable endowed with cell targeting properties intrinsically integrated into the amino acid sequences of the utilized peptides, which indeed turn them into promising nanodevices for biomedical applications.

Thermal behavior of a lipid-protein membrane model and the effects produced by anesthetics and neurotransmitters.

Despite decades of intense research to understand the phenomenon of anesthesia and its membrane-related changes in neural transmission, where lipids and proteins have been proposed as primary targets of anesthetics, the involved action mechanisms remain unclear. Based on the overall agreement that anesthetics and neurotransmitters induce particular modifications in the plasma membrane of neurons, triggering specific responses and changes in their energetic states, we present here a thermal study to investigate membrane effects in a lipid-protein model made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine and albumin from chicken egg white under the influence of neurotransmitters and anesthetics. First, we observe how ovalbumin, ovotransferrin, and lysozyme (main albumin constituents from chicken egg white) interact with the lipid membrane enhancing their lipophilic character while exposing their hydrophobic domains. This produces a lipid separation and a more ordered hybrid lipid-protein assembly. Second, we measured the thermotropic changes of this assembly induced by acetylcholine, γ-aminobutiric acid, tetracaine, and pentobarbital. Although the protein in our study is not a receptor, our results are striking, for they give evidence of the great importance of non-specific interactions in the anesthesia mechanism.

A technique based on droplet evaporation to recognize alcoholic drinks.

Chromatography is, at present, the most used technique to determine the purity of alcoholic drinks. This involves a careful separation of the components of the liquid elements. However, since this technique requires sophisticated instrumentation, there are alternative techniques such as conductivity measurements and UV-Vis and infrared spectrometries. We report here a method based on salt-induced crystallization patterns formed during the evaporation of alcoholic drops. We found that droplets of different samples form different structures upon drying, which we characterize by their radial density profiles. We prove that using the dried deposit of a spirit as a control sample, our method allows us to differentiate between pure and adulterated drinks. As a proof of concept, we study tequila.

Ionic interactions determine the morphology of dried alkali/liposome suspension droplets.

We sought to understand why saline drops produce intriguing patterns when drying in the presence of zwitterionic liposomes. Specifically, we would like to comprehend why the nature of such patterns is hierarchically driven by the Hofmeister series. The liposome suspension is made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) with alkali metal chlorides. A complexity analysis of the patterns gives a fractal dimension around 1.71, which means that the drying process resembles a DLA mechanism. A physicochemical study, including the determination of zeta potential, molecular dynamics simulations, microrheology, and calorimetry, supports the fact that electrostatic interactions among head groups of phospholipids with alkali cations are the driven forces behind the assembling of the observed structures. Moreover, we found that the morphology of the dried droplets is sensitive to the substrate. Our findings could be used in a biological context, for example, to characterize cells in ionic media.

The calorimetric properties of liposomes determine the morphology of dried droplets.

The evaporation of liquid droplets deposited on a substrate is a very complex phenomenon. Driven by capillary and Marangoni flows, particle-particle and particle-substrate interactions, the deposits they leave are vestiges of such complexity. We study the formation of patterns during the evaporation of liposome suspension droplets deposited on a hydrophobic substrate at different temperatures. We observed that as we change the temperature of the substrate, a morphological phase transition occurs at a given temperature Tm. This temperature corresponds to the gel-fluid lipid melting transition of the liposome suspension. Optical microscopy and atomic force microscopy are used to study the morphology of the patterns. Based on the radial density profiles we found that all structures can be classified into two groups: patterns composed by nearly uniform deposition (below Tm) and prominent structures containing randomly distributed voids (above Tm).

Anesthetic diffusion through lipid membranes depends on the protonation rate.

Hundreds of substances possess anesthetic action. However, despite decades of research and tests, a golden rule is required to reconcile the diverse hypothesis behind anesthesia. What makes an anesthetic to be local or general in the first place? The specific targets on proteins, the solubility in lipids, the diffusivity, potency, action time? Here we show that there could be a new player equally or even more important to disentangle the riddle: the protonation rate. Indeed, such rate modulates the diffusion speed of anesthetics into lipid membranes; low protonation rates enhance the diffusion for local anesthetics while high ones reduce it. We show also that there is a pH and membrane phase dependence on the local anesthetic diffusion across multiple lipid bilayers. Based on our findings we incorporate a new clue that may advance our understanding of the anesthetic phenomenon.