Abstract
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.
Highlights
Hundreds of molecules produce anesthesia, but only two models explain how they inhibit nerve impulses [1,2,3]
Sperm motility information is analysed through the temporal development of the cell motility parameter (CMP) t, which increases as the motility decreases [26]
There is a permanent electrostatic repulsion between the electric dipole heads of the lipids, which are in a favourable interaction with water molecules
Summary
Hundreds of molecules produce anesthesia, but only two models explain how they inhibit nerve impulses [1,2,3]. The oldest and most succinct model, hints toward a thermodynamic explanation. It states that anesthetic molecules act in the lipids medium of neuron cells and that the more hydrophobic such molecules are, the higher their narcotic potency. The newest and more accepted model, professes that the narcotic action occurs over specific binding sites of membrane proteins. Even if this second framework requires a diligent search of the binding sites for the innumerable anesthetic molecules, research and support on the protein paradigm is overwhelming. The old rule, which states that the anesthetic potency is proportional to anesthetic solubility in membranes [4], remains infallible: no anesthetic molecule exists, whatsoever, with a partition coefficient less than one
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