Modulation of Synaptosomal Plasma Membrane-Bound Enzyme Activity Through the Perturbation of Plasma Membrane Lipid Structure by Bupivacaine

Abstract

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[degree sign]C and 24.5 +/- 1.2[degree sign]C (mean +/- SD), respectively, in control SPM, which shifted to 17.1 +/- 0.95[degree sign]C (P < 0.01) and 18.2 +/- 0.85[degree sign]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[degree sign]C) and the BPV-treated SPM (17.5 +/- 0.8[degree sign]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. Implications: 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. (Anesth Analg 1997;85:1337-43)