Measurement of the Interaction between Protein and Anesthetics Using Ion Selective Electrode

Abstract

Anesthetics have in common the capacity to partition indiscriminately into all biological membranes and act as general perturbants of the membrane structure and function. However, anesthetic mechanisms have not yet been clarified. Some measurement techniques are used to investigate the interaction between anesthetic and biological materials. Thus, in this research we examined the utility of the electrode selectively sensitive to local anesthetics as a measurement technique of the interaction of the bovine serum albumin (BSA) with local anesthetics. The electromotive forces (EMF) of the local anesthetic dibucaine and tetracaine cation-selective electrodes were measured relative to an Ag-AgCl reference electrode in both the absence and presence of BSA at pH 5.5. In the absence of BSA, both the dibucaine and tetracaine electrodes showed a linear response with a Nernstian slope over the concentration of 10−5 mol dm−3. Most of local aneshetic molecules must exist as the protonated cation at pH 5.5, judging from the pKa values. In the presence of BSA, the response curve was shifted toward the higher concentration of anesthetics, which means a decrease of the concentration of free anesthetic cation due to binding to BSA. The binding isotherms of anesthetics to BSA were calculated from a pair of response curves. The slope of the binding isotherm increased steeply above a certain concentration of local anesthetics, which means that the binding form of local anesthetic into BSA is multiple-step.