Lin, C. T. (Chhui-Tsu)
M.S. (Master of Science)
Department of Chemistry
Local anesthetics--Physiological transport||Membranes (Biology)--Mechanical properties||Biological transport
The diffusive transport of local anaesthetics across two biomembranes (pig spinal cord and pig heart) and one protein (bovine eye lens crystallin) are investigated by steady-state and time-resolved emission spectroscopy at 298 and 77 K. The well-defined photophysical properties of uncharged (free base) and charged(protonated) forms of local anesthetic drugs were used as "direct" optical probes for identifying the solubilization of drug species in and out of membranes. The dibucaine-HCl (DH+) is deprotonated at extracellular surface of the pig spinal cord and become a neutral form to enter the hydrophobic part (white matter) of the spinal cord. After the drug passes through the white matter, it is reprotonated and enters the hydrophilic fluid. When dibucaine-HCl (DH+) is incorporated into pig heart, DH+ is also deprotonated at the extracellular surface of the heart membrane. The deprotonatd neutral form (D) soon results in hydrogen-bonded drug species, located probably at the polar region of the membrane interface. When the hydrogen-bonded dibucaine reaches the cytoplasmic side of the heart membrane, it is reprotonated. Tryptophan in bovine eye lens crystallin displays different photophysical properties when it (tryptophan) locates at different microenvironments. DH+ is depronated at the surface of a-, (JH crystallin. The resulting D enter the hydrophobic part of the protein and quenches the tryptophan located at that part. The process of dibucaine-HCl transport across membranes such as pig spinal cord, pig heart and bovine eye lens crystallin is very similar. At the surface of pig spinal cord, pig heart and eye lens crystallin, dibucaine-HCl (DH+) is deprotonated and neutral dibucaine(D) is partitioned inside the membrane. The dibucaine species released from the inner membrane of pig spinal cord is not dibucaine-HCl, but rather an enzymatically hydrolyzed species. It is proposed that molecular action of local anesthetics is not the charged form acting on the hydrophillic surface, but indeed is the uncharged form (neutral) taking action at the hydrophobic region of biomembranes.
Wei, Taolin, "Molecular species of local anesthetics in drug transport across membranes" (1997). Graduate Research Theses & Dissertations. 4019.
x, 139 pages
Northern Illinois University
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