Ca2+-mediated enhancement of anesthetic diffusion across phospholipid multilamellar systems.

Although sharing common properties with other divalent cations, calcium ions induce fine-tuned electrostatic effects essential in many biological processes. Not only related with protein structure or ion channels, calcium is also determinant for other biomolecules such as lipids or even drugs. Cellular membranes are the first interaction barriers for drugs. Depending on their hydrophilic, hydrophobic or amphipathic properties, they have to overcome such barriers to permeate and diffuse through inner lipid bilayers, cells or even tissues. In this context, the role of calcium in the permeation of cationic amphiphilic drugs (CADs) through lipid membranes is not well understood. We combine differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) to investigate the effect of Ca2+ on the interlamellar diffusion kinetics of the local anesthetic tetracaine (TTC) in multilamellar artificial membrane systems. Our DSC results show the interesting phenomenon that TTC diffusion can be modified in two different ways in the presence of Ca2+. Furthermore, TTC diffusion exhibits a thermal-dependent membrane interaction in the presence of Ca2+. The FTIR results suggest the presence of ion-dipole interactions between Ca2+ and the carbonyl group of TTC, leading us to hypothesize that Ca2+ destabilizes the hydration shell of TTC, which in turn diffuses deeper into the multilamellar lipid structures. Our results demonstrate the relevance of the Ca2+ ion in the drug permeation and diffusion through lipid bilayers.

Dehydration/Rehydration Cycles for Mixing Phospholipids without the Use of Organic Solvents.

An environmentally friendly and straightforward dehydration/rehydration method for glycerophospholipid mixing that avoids the use of organic solvents, cosolvents, or additives was developed. We prepared binary mixtures of zwitterionic and anionic glycerophospholipids using only deionized water in the entire mixing process. The resulting lipid films were subsequently reconstituted in vesicular form and compared to controls using differential scanning calorimetry. The calorimetric scans revealed no significant differences between mixing methods for any of the studied cases. These findings suggest that the developed dehydration/rehydration procedure creates a sample with equivalent compositional uniformity than the conventional solvent evaporation technique.

The influence of non polar and polar molecules in mouse motile cells membranes and pure lipid bilayers.

We report an experimental study of mouse sperm motility that shows chief aspects characteristic of neurons: the anesthetic (produced by tetracaine) and excitatory (produced by either caffeine or calcium) effects and their antagonic action. While tetracaine inhibits sperm motility and caffeine has an excitatory action, the combination of these two substances balance the effects, producing a motility quite similar to that of control cells. We also study the effects of these agents (anesthetic and excitatory) on the melting points of pure lipid liposomes constituted by 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and dipalmitoyl phosphatidic acid (DPPA). Tetracaine induces a large fluidization of the membrane, shifting the liposomes melting transition temperature to much lower values. The effect of caffeine is null, but its addition to tetracaine-doped liposomes greatly screen the fluidization effect. A high calcium concentration stiffens pure lipid membranes and strongly reduces the effect of tetracaine. Molecular Dynamics Simulations are performed to further understand our experimental findings at the molecular level. We find a strong correlation between the effect of antagonic molecules that could explain how the mechanical properties suitable for normal cell functioning are affected and recovered.