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Anesthetic diffusion through lipid membranes depends on the protonation rate.

Pérez-Isidoro R, Sierra-Valdez FJ, Ruiz-Suárez JC - Sci Rep (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: CINVESTAV-Monterrey, PIIT, Nuevo León, 66600, México.

ABSTRACT
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.

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Related in: MedlinePlus

The diffusion kinetics of TCC modulated by CA.MLV liposomes were prepared in different CA solutions adjusted to pH 5 (HCl/NaOH). After 10 min of the TCC (25 mM) addition, a sequence of 10 heating scans was taken by the DSC. (a) The first scans of H2O (black circles), malic acid (A, red squares), citric acid (B, blue up triangles), formic acid (C, green down triangles) and glycolic acid (D, magenta stars) were sorted according to their stage in the diffusion kinetics. (b) Enthalpies of H1 and H2 as function of time for both H2O and the respective CA. Upper grey dashed line stands for the ΔHmax (~34.2 kJ/mol), which remains constant throughout the CA experiments. (c) The respective κ values were obtained from the best-fit of the diffusion model as illustrated in b. Note that the ‘single-phase transition’ obtained by general anesthetics may obey the diffusion model under a very high κ value.
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f5: The diffusion kinetics of TCC modulated by CA.MLV liposomes were prepared in different CA solutions adjusted to pH 5 (HCl/NaOH). After 10 min of the TCC (25 mM) addition, a sequence of 10 heating scans was taken by the DSC. (a) The first scans of H2O (black circles), malic acid (A, red squares), citric acid (B, blue up triangles), formic acid (C, green down triangles) and glycolic acid (D, magenta stars) were sorted according to their stage in the diffusion kinetics. (b) Enthalpies of H1 and H2 as function of time for both H2O and the respective CA. Upper grey dashed line stands for the ΔHmax (~34.2 kJ/mol), which remains constant throughout the CA experiments. (c) The respective κ values were obtained from the best-fit of the diffusion model as illustrated in b. Note that the ‘single-phase transition’ obtained by general anesthetics may obey the diffusion model under a very high κ value.

Mentions: Proton transfer plays an essential role in many biological systems53545556. Some reports have shown proton transfer rates in the order of femtoseconds - microseconds, highly depending on the chemical structure of the target molecule and its environment57585960. Recently, it has been reported slight but significant differences in the proton transfer rates in the lysosome region between normal lung cells (30 ps) and lung cancer cells (25 ps)61. To determine how the TCC diffusion kinetics is modulated by the IEPR, we used four weak carboxylic acids (CA) (formic, glycolic, citric and malic acid). The selected CA contains different ‘radical groups’ bonded to the carboxylic group. Since the CA are not strictly buffers, we carefully adjusted the pH to 5 before introducing the sample into the DSC equipment. This pH is a representative value of the pH range of ‘clinical conditions’, which implies a constant [H+] concentration. This argument therefore allows the ‘radical group’ of CA to be the free variable, since that the chemical structure of each ‘radical group’ provides to the medium a particular proton transfer rate, giving as a result an IEPR. Figure 5a displays the first scan of the respective CA experiment. It is easy to note that the ‘H2O’ case shows the earliest stage in the kinetic process, comprising only two-coupled equilibrium reactions (H2O-TCC). At pH 5, the constant interchange between species 2 (97.06%) and 3 (2.9%) of TCC is more favored than with the specie 1 (0.04%) (Fig. 4c upper). On the other hand, for the CA case, the subsequent stages are given by malic, citric, formic and glycolic acid (see Fig. 5a, A, B, C, D respectively), showing in their first scan an increasingly advanced stage of the kinetic diffusion. The CA case now corresponds to three-coupled equilibrium reactions (H2O-TCC-CA) with different proton transfer rates. Control experiments where carried out to illustrate that CA do not perturb the DPPC membranes (Supplementary Fig. S2).


Anesthetic diffusion through lipid membranes depends on the protonation rate.

Pérez-Isidoro R, Sierra-Valdez FJ, Ruiz-Suárez JC - Sci Rep (2014)

The diffusion kinetics of TCC modulated by CA.MLV liposomes were prepared in different CA solutions adjusted to pH 5 (HCl/NaOH). After 10 min of the TCC (25 mM) addition, a sequence of 10 heating scans was taken by the DSC. (a) The first scans of H2O (black circles), malic acid (A, red squares), citric acid (B, blue up triangles), formic acid (C, green down triangles) and glycolic acid (D, magenta stars) were sorted according to their stage in the diffusion kinetics. (b) Enthalpies of H1 and H2 as function of time for both H2O and the respective CA. Upper grey dashed line stands for the ΔHmax (~34.2 kJ/mol), which remains constant throughout the CA experiments. (c) The respective κ values were obtained from the best-fit of the diffusion model as illustrated in b. Note that the ‘single-phase transition’ obtained by general anesthetics may obey the diffusion model under a very high κ value.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269894&req=5

f5: The diffusion kinetics of TCC modulated by CA.MLV liposomes were prepared in different CA solutions adjusted to pH 5 (HCl/NaOH). After 10 min of the TCC (25 mM) addition, a sequence of 10 heating scans was taken by the DSC. (a) The first scans of H2O (black circles), malic acid (A, red squares), citric acid (B, blue up triangles), formic acid (C, green down triangles) and glycolic acid (D, magenta stars) were sorted according to their stage in the diffusion kinetics. (b) Enthalpies of H1 and H2 as function of time for both H2O and the respective CA. Upper grey dashed line stands for the ΔHmax (~34.2 kJ/mol), which remains constant throughout the CA experiments. (c) The respective κ values were obtained from the best-fit of the diffusion model as illustrated in b. Note that the ‘single-phase transition’ obtained by general anesthetics may obey the diffusion model under a very high κ value.
Mentions: Proton transfer plays an essential role in many biological systems53545556. Some reports have shown proton transfer rates in the order of femtoseconds - microseconds, highly depending on the chemical structure of the target molecule and its environment57585960. Recently, it has been reported slight but significant differences in the proton transfer rates in the lysosome region between normal lung cells (30 ps) and lung cancer cells (25 ps)61. To determine how the TCC diffusion kinetics is modulated by the IEPR, we used four weak carboxylic acids (CA) (formic, glycolic, citric and malic acid). The selected CA contains different ‘radical groups’ bonded to the carboxylic group. Since the CA are not strictly buffers, we carefully adjusted the pH to 5 before introducing the sample into the DSC equipment. This pH is a representative value of the pH range of ‘clinical conditions’, which implies a constant [H+] concentration. This argument therefore allows the ‘radical group’ of CA to be the free variable, since that the chemical structure of each ‘radical group’ provides to the medium a particular proton transfer rate, giving as a result an IEPR. Figure 5a displays the first scan of the respective CA experiment. It is easy to note that the ‘H2O’ case shows the earliest stage in the kinetic process, comprising only two-coupled equilibrium reactions (H2O-TCC). At pH 5, the constant interchange between species 2 (97.06%) and 3 (2.9%) of TCC is more favored than with the specie 1 (0.04%) (Fig. 4c upper). On the other hand, for the CA case, the subsequent stages are given by malic, citric, formic and glycolic acid (see Fig. 5a, A, B, C, D respectively), showing in their first scan an increasingly advanced stage of the kinetic diffusion. The CA case now corresponds to three-coupled equilibrium reactions (H2O-TCC-CA) with different proton transfer rates. Control experiments where carried out to illustrate that CA do not perturb the DPPC membranes (Supplementary Fig. S2).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: CINVESTAV-Monterrey, PIIT, Nuevo León, 66600, México.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus