Modulation of synaptosomal plasma membrane-bound enzyme activity through the perturbation of plasma membrane lipid structure by bupivacaine.
We investigated modulations of lipid dynamics and lipid-protein interactions of rat brain synaptosomal plasma membrane (SPM) as one of the possible mechanisms by which the local anesthetic bupivacaine (BPV) has an adverse effect on nerve cell function, with SPM-bound enzyme activity used as a functional probe. The kinetics of BPV impact on the activity of the endoenzymes Ca2+/Mg2+-stimulated ATPase and Na+/K+-stimulated ATPase and the active concentrations of the drug were relevant to those that produce biphasic systemic toxicity. Arrhenius plots of these enzymes showed a transition temperature of 26.6 +/- 1.8 degrees C and 24.5 +/- 1.2 degrees C (mean +/- SD), respectively, in control SPM, which shifted to 17.1 +/- 0.95 degrees C (P < 0.01) and 18.2 +/- 0.85 degrees C (P < 0.05) in SPM treated with 10(-5) M BPV. The Hill coefficients for the allosteric inhibition of Ca2+/Mg2+-stimulated ATPase by Na+ and Na+/K+-stimulated ATPase by fluoride decreased from 1.73 +/- 0.20 and 1.95 +/- 0.25, respectively, in controls to 0.92 +/- 0.09 (P < 0.001) and 1.09 +/- 0.11 (P < 0.001) in the presence of 10(-5) M BPV. The fluidity perturbation in the microenvironment of the ectoenzyme acetylcholinesterase was observed only at 5 x 10(-3) M BPV, as confirmed by the disparity in transition temperature between the controls (22.3 +/- 1.2 degrees C) and the BPV-treated SPM (17.5 +/- 0.8 degrees C, P < 0.01) and that in the Hill coefficient in the two groups: 2.15 +/- 0.24 and 0.97 +/- 0.12 (P < 0.001), respectively.


CONCLUSIONS
We propose that under physiological conditions, the neutral and protonated forms of local anesthetics can affect nerve cell function through the asymmetric perturbation of the membrane lipid structure, accompanied by synaptosomal plasma membrane-bound enzyme dysfunction.
Kopeikina
L T
LT
Department of Experimental Physiology, Medical School, Aretaeion Hospital, University of Athens, Greece.
Kamper
E F
EF
Siafaka
I
I
Stavridis
J
J
D015720:5'-Nucleotidase / Q000378:metabolism; D000110:Acetylcholinesterase / Q000378:metabolism; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D008297:Male; D008560:Membrane Fluidity / Q000187:drug effects; D008563:Membrane Lipids / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013570:Synaptic Membranes / Q000187:drug effects / Q000201:enzymology*; D013696:Temperature
D000779:Anesthetics, Local; D008563:Membrane Lipids; D000110:Acetylcholinesterase; D015720:5'-Nucleotidase; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D002045:Bupivacaine