Hiromu Satake

Partitioning of local anesthetic dibucaine into bilayer membranes of dimyristoylphosphatidylcholine

Abstract Binding of a local anesthetic dibucaine to dimyristoylphosphatidylcholine (DMPC) bilayer membranes was studied by using an ion-selective electrode sensitive to dibucaine cation. DMPC bilayer membrane-buffer partition coefficient was directly determined as a function of anesthetic concentration, temperature and pH. The limiting partition coefficient extrapolated to infinite dilution was employed because the values of partition coefficients were dependent upon the dibucaine concentration. DMPC multilamellar vesicles undergo the thermotropic pretransition from the lamellar gel ( L β ′ ) to the ripple gel ( P β ′ ) phase as well as the main transition from the P β ′ phase to the liquid crystal ( L α ) phase. The limiting partition coefficients at pH 5.4 were 2000, 5500 and 32 000 for the L β ′ , P β ′ and L α phases, respectively. Each of the three states of membranes exhibited a different receptivity to dibucaine partitioning. The limiting partition coefficients were determined as a function of pH at the temperatures corresponding to three states of membranes. The partition coefficients of charged and uncharged anesthetic dibucaine into the DMPC bilayer membranes were estimated from the pH-dependence of the limiting partition coefficients. The three states of DMPC membranes were more receptive to the uncharged dibucaine than the charged species.

Pranidipine, a new 1, 4-dihydropyridine calcium channel blocker, enhances cyclic GMP-independent nitric oxide-induced relaxation of the rat aorta

Pranidipine, a new calcium channel modulator, prolonged endothelium-dependent relaxation induced by acetylcholine in a aortic ring preparation, contracted with prostaglandin F2α. This action was not shared by amlodipine. The effect was not modified by indomethacin, suggesting that the action of pranidipine does not involve prostanoid metabolism. NG-nitro-L-arginine completely prevented the action of Pranidipine. The drug affected neither nitric oxide (NO) synthase activity nor the level of cyclic GMP in the vessel. Pranidipine did not affect the sensitivity of the contractile proteins to calcium. Pranidipine also did not alter cyclic GMP-induced relaxation in a-toxinskinned vascular preparations. Pranidipine also prolonged glyceryl trinitrate-induced relaxation in the endothelium denuded rat aorta. Furthermore, pranidipine enhanced relaxation of the aorta induced by glyceryl trinitrate even in the presence of methylene blue, a guanylyl cyclase inhibitor. This action was not modified by iberiotoxin or by charybdotoxin, two inhibitors of the calciumactivated potassium channel. The results strongly suggest that pranidipine enhances cyclic GMPindependent NO-induced relaxation of smooth muscle by a mechanism other than through NOinduced hyperpolarization. These effects were in direct contrast to amlodipine, another new 1,4dihydropyridine calcium antagonist.

Potentiometric argentimetric method for the successive titration of sulphide and dissolved sulphur in polysulphide solutions.

Sulphide sulphur and dissolved sulphur in a polysulphide solution can be successively determined with satisfactory accuracy and reproducibility by potentiometric argentimetry in which a sulphide-selective indicator electrode is used. Before the titration, polysulphide ions need to be converted by an excess of potassium cyanide into thiocyanate and sulphide ions. The excess of cyanide ions is masked with formaldehyde and sulphuric acid, then the solution is made alkaline with ammonia and titrated with silver nitrate till the first end-point is reached (sulphide sulphur). After the acidification of the solution with sulphuric acid, the titration is continued till the second end-point is attained (dissolved sulphur).

Membrane-buffer partition coefficients of a local anesthetic tetracaine monitored by an anesthetic sensor; effects of temperature and pH.

Binding of a local anesthetic tetracaine (TC) to dimyristoylphosphatidylcholine (DMPC) bilayer membrane was studied by the potentiomerty with an ion-selective electrode sensitive to TC cation. DMPC membrane-buffer partition coefficient (K(app)) was determined in mole fraction unit as a function of pH for the lamellar gel (at 12 degrees C), ripple gel (at 20 degrees C), and liquid crystal (at 30 degrees C) phases. The partition coefficients of charged (K+) and uncharged TC (K0) into the DMPC membranes were estimated from the pH-dependence of K(app). The three states of DMPC membranes were more receptive to the uncharged TC than the charged species.

Colloidal properties of aqueous local anesthetic tetracaine solutions

Abstract The present study includes the colloidal solution properties of a local anesthetic, tetracaine hydrochloride (C15H24N2O2·.HCl). The CMC of C15H24N2O2·.HCl was determined using a coated wire electrode that is selectively sensitive to a local anesthetic cation. The effects of added salt (NaCl) and temperature on the CMC were studied. A linear relationship between the logarithm of the CMC and the counterion concentration was confirmed at 25°C. The CMC in the absence of added NACl tends to increase as the temperature rises in the range 15–35°C. The enthalpy change on micellization was estimated to be –3.7 kJ mol−1 from the temperature dependence of the CMC. The Krafft phenomenon was observed from heating scans obtained by differential scanning calorimetry. The transition enthalpy from the hydrated solid to the micellar solution was 29.4 kJ mol−1. Another transition associated with an enthalpy change of 1.7 kJ mol−1 was observed just below the Krafft temperature, which was assigned to the transition between lyotropic liquid crystals.

Local anesthetic-sensitive electrodes : preparation of coated-wire electrodes and their basic properties in vitro

Coated-wire electrodes with local anesthetic (LA) cation-selective membranes were prepared, and their properties in vitro were investigated. Copper wires (0.8-mm diameter) were coated with gel membranes of 110 mg of poly(vinyl chloride), 5 mg of ion pairs of tetraphenylborate anion with LA cation, 100 mg of dioctylphtalate, and 1.5 mL of tetrahydrofuran. This was the composition determined to be most suitable. Their electromotive force relative to an Ag/AgCl electrode was measured in LA solutions. The lidocaine, dibucaine, and mepivacaine electrodes all showed good Nernstian response at 25 degrees C in aqueous solutions in the concentration ranges of 1 x 10(-4) to 1 x 10(-2) mol/L, 4 x 10(-5) to 1 x 10(-2) mol/L, and 5 x 10(-5) to 1 x 10(-2) mol/L, respectively. The response time was within 10 s. The electrode potential decreased as the pH in the solution increased, with a corresponding decrease of the protonated form of LA. The hydrophobic nature of the LA was closely related to the electromotive force and to the selectivity of the electrode toward various LA cations. Dibucaine, the most hydrophobic, had the highest electrode potential. The more hydrophobic the LA of the electrode, the less it is interfered with by other LA molecules. The more hydrophobic the interferent cation, the more it acts on the electrode potential. The electrode system could also measure LA in human plasma at 37 degrees C, although the responsiveness was depressed in the low concentration range owing to binding of LA to the serum protein.(ABSTRACT TRUNCATED AT 250 WORDS)

A Coated Wire Electrode Sensitive to Tetraphenylphosphonium Ion for Measurement of the Mitochondrial Membrane Potential

Abstract A coated wire electrode selectively sensitive to tetraphenyl-phosphonium(TPP+) ion has been developed, which employs TPP+-tetraphenylborate ion-pair as an ion sensor, dioctylphtalate as a plasticizer and poly(vinyl chloride) as an inert matrix. The electrode exhibits a linear response within the concentration range 10−3 - 3×10−7 M, with a Nernstian slope(56.5 mV/decade). The reproducibility, stability, response time and selectivity were also investigated. The electrode exhibits very good selectivity for TPP+ ion against the substances used for the measurement of membrane potential of mitochondria. The electrode was applied satisfactorily to the estimation of mitochondria1 membrane potential.

Studies on analytical methods by amperometric titration using a rotating platinum electrode: Part 47. Successive Determination of L-Cysteine and L-Cystine by Amperometric Titration

Abstract The successive determination of {spl}-cysteine and {spl}-cystine (2–5 μmol of each) in mixtures is achieved by amperometric titration with standard potassium iodate solution using a rotating platinum wire electrode at + 0.6 V vs. SCE. {spl}-Cysteine is titrated in acidic bromide-containing solution; sodium chloride (15 g) is then added and the titration is continued to determine L-cystine.

Solubilization study of local anesthetics into sodium dodecyl sulfate micelle using anesthetic cation selective electrodes.

The free concentrations of local anesthetic cations in equilibrium with sodium dodecyl sulfate (SDS) micelle which solubilized the anesthetic were determined by using ion-selective electrodes sensitive to local anesthetics, procaine (PC), lidocaine (LC), and mepivacaine (MC). Solubilizate distribution between water and SDS micelle was analyzed by means of the stepwise mass-action model. Association constant, K(1), was found to depend upon the anesthetic concentration, which decreased exponentially as the concentration of free anesthetic increased. Therefore, K(1) should include the interaction function φ(A) as K(1)=K(int)exp{-φ(A)} where K(int) is an intrinsic association constant. φ(A) is an increasing function of the anesthetic concentration, which means that occupation of a solubilization site by a local anesthetic cation makes sequential solubilization more difficult. The binding affinity of an anesthetic with SDS micelle increased in the following order PC<LC<MC.The critical micelle concentration (CMC) of mixed micelle was determined as a function of the concentration of free anesthetic. The CMC decreased with an increasing amount of anesthetics solubilized. All the anesthetic compositions in the micelle calculated thermodynamically from the CMC data were larger than the corresponding ones in the aqueous phase. Although the local anesthetics used here do not form micelles by themselves, the CMC vs composition curve can be regarded as a part of a micellar phase diagram showing the negative azeotropic behavior, which reflects the attractive interaction between the anionic surfactant micelle and the local anesthetic cation.

Intra-axonal continuous measurement of lidocaine concentration and pH in squid giant axon

PurposeTo measure the dynamic penetration process of lidocaine, lidocaine concentration (Ci) and pH (pHi) in squid giant axon, and to determine the times and Ci of disappearance and reappearance of action potentials (AP).MethodsLidocaine solutions adjusted to four different pHs (pH = 5.5, 6.8, 7.8 and 9.0) were externally administered to the axon and Ci and pHi were measured using lidocaine and pH microsensors. The times and Ci when the AP just disappeared and reappeared were recorded. In addition, for comparison with Ci, the lidocaine content in the whole axon (Cw) was measured with high-performance liquid chromatography (HPLC).ResultsThe Ci (charged plus uncharged) was 1.5 times greater than the uncharged form of administered lidocaine. The changes in pHi depended on the increase in Ci. The AP disappeared only after administration of high pH lidocaine solutions (pH = 7.8, 9.0) and reappeared by washing out the solution in the chamber. Nerve block occurred more rapidly at pH 9.0 than at pH 7.8, and the time after washing out the lidocaine was longer at pH 9.0 than at pH 7.8. The mean Ci and charged lidocaine concentration in the axoplasm, when the AP disappeared or reappeared, were lower at pH 9.0 than at pH 7.8 (P < 0.05).ConclusionUncharged lidocaine penetrates the axon membrane to the axoplasm where it changes to the charged form and is concentrated in the axon membrane and axoplasm. External application of uncharged lidocaine plays a role in modulating nerve conduction.RésuméObjectifMesurer le processus de pénétration dynamique de la lidocaïne, la concentration de lidocaïne (Ci) et le pH (pHi) dans un axone géant de calmar et déterminer les temps et la Ci de disparition et de réapparition des potentiels d’action (PA).MéthodeLes solutions de lidocaïne, préparées selon quatre pH différents (pH = 5,5; 6,8; 7,8 et 9,0), ont été administrées sur la paroi externe de l’axone et la Ci et le pHi ont été mesurés en utilisant de la lidocaïne et des microdétecteurs de pH. Les temps et les Ci correspondants au moment de disparition et de réapparition du PA ont été enregistrés. De plus, pour comparer avec la Ci, le contenu de lidocaïne de l’axone complet (Cc) a été mesuré par Chromatographie liquide à haute pression (CLHP).RésultatsLa Ci (ionisée plus non ionisée) a été 1,5 fois plus élevée que la forme non ionisée de lidocaïne administrée. Les changements de pHi dépendaient de l’augmentation de Ci. Le PA a disparu seulement après l’administration de solutions de lidocaïne à pH élevé (pH = 7,8; 9,0) et a réapparu quand on a rincé la solution dans la cuve. Le blocage nerveux est survenu plus rapidement sous un pH de 9,0 que sous un pH de 7,8 et le temps après le rinçage de la lidocaïne a été plus long sous un pH de 9,0 que sous un pH de 7,8. La Ci moyenne et la concentration de lidocaïne ionisée dans l’axoplasme, au moment où le PA disparaissait ou réapparaissait, ont été plus faibles sous un pH de 9,0 que sous un pH de 7,8 (P < 0,05).ConclusionLa lidocaïne non ionisée pénètre la membrane axonale jusqu’à l’axoplasme où elle se transforme en lidocaïne ionisée et est concentrée dans la membrane axonale et l’axoplasme. L’application externe de lidocaïne non ionisée joue un rôle en modulant la conduction nerveuse.