Local anesthetic-membrane interaction: a multiequilibrium model

Preparation and Antiproliferative Activity of Liposomes Containing a Combination of Cisplatin and Procainamide Hydrochloride

We have previously reported the enhancement of the antiproliferative and apoptotic activities of cis-diamminedichloroplatinum(II) (DDP) when it is coadministered with a class I antiarrhythmic drug procainamide hydrochloride (PA). Here, we determined the antiproliferative activity of DDP, either in solution or loaded in liposomes, in the presence of PA, in the bulk solution, or directly embedded in liposomes together with DDP. Our results show that PA potentiates the activity of DDP-liposomes and that this effect is maintained at least in some of the investigated cell types when both drugs were mixed and loaded together into liposomes.

Thermodynamics of partitioning of benzocaine in some organic solvent/buffer and liposome systems

The thermodynamics of partitioning of benzocaine (BZC) were studied in octanol/buffer (ROH/W), isopropyl myristate/buffer (IPM/W), cyclohexane/buffer (CH/W), and dimyristoyl phosphatidylcholine (DMPC) and dipalmitoyl phosphatidylcholine (DPPC) liposome systems. In all cases the partition coefficients were greater than unity; therefore the free energies of transfer were negative, that is, the processes of transfer of BZC from aqueous media to organic systems were spontaneous. The partition coefficients were approximately three-fold higher in DMPC liposomes compared with the ROH/W system in the 30 degrees -40 degrees C temperature range. The enthalpies of transfer from aqueous media to ROH and IPM were negative, but positive for CH, while this property was negative for DMPC liposomes and positive for DPPC liposomes. The entropies of transfer were positive in almost all cases, except for DMPC. The results presented here confirm the lipophilic nature of BZC.

Membrane effects of ropivacaine compared with those of bupivacaine and mepivacaine

We compared the effects of ropivacaine, bupivacaine and mepivacaine on membrane lipids in an attempt to determine the anaesthetic mechanism of ropivacaine with structure-dependent potency. The membrane effects were determined by measuring anaesthetic-induced changes in the phase transition temperature and the fluorescence polarization of liposomal membranes prepared with cholesterol and phosphatidylcholine. Bupivacaine, ropivacaine and mepivacaine depressed the membrane lipid phase transition and decreased the polarization of liposomal membranes at 0.0625-1.0 mg/mL, indicating that these anaesthetics fluidize membranes at concentrations lower than those in clinical use. Ropivacaine and bupivacaine were effective in fluidizing the membrane core rather than the membrane surface, whereas mepivacaine was a membrane fluidizer acting equally on both regions. In the comparison of membrane fluidization at an equimolar concentration (3.0 mmol/L), ropivacaine was found to be less potent than bupivacaine and more potent than mepivacaine. This membrane-fluidizing potency was also consistent with the hydrophobic properties of these substances evaluated by reversed-phase chromatography. Structure-dependent membrane fluidization associating with hydrophobicity appears to underlie the local anaesthetic effect of ropivacaine as well as those of bupivacaine and mepivacaine.

Purification of chlorpromazine-sensitive GTPase from rat cerebral cortex

The chlorpromazine-sensitive GTPase from the cell membrane of rat cerebral cortex was purified to homogenity by using DEAE Bio-Gel A agarose, hydroxyapatite and heparin agarose chromatography. The purified chlorpromazine-sensitive GTPase was purified 370-fold to obtain a final specific activity of 40 mumol GTP hydrolyzed2min/mg protein. The purified enzyme was inhibited by chlorpromazine but not by compound 48/80. Magnesium was required for its activity instead of calcium. The purified enzyme had an apparent pH optimum of 8.0, and molecular weight was estimated to be 58,000.

Local anesthetic-phospholipid interactions. Effects of ionic strength, temperature, and phospholipid mixtures on the binding of dibucaine to phospholipids

The nature of the interaction of amphipathic drugs, such as dibucaine, with phospholipid bilayer membranes was investigated using equilibrium dialysis. Profiles for the binding of cationic dibucaine to unilamellar vesicles were obtained at different temperature and ionic strengths, and for mixtures of neutral phospholipid dimyristylphosphatidylcholine (DMPC) with negatively charged dimyristylphosphatidylglycerol (DMPG). The degree of binding of the cationic drug at pH 5 was found to be higher at temperatures above the Tm of DMPC (24 degrees C) than below Tm. Also enhanced drug binding was found to occur as the concentration of monovalent salt was increased (0.01-0.85 M) and as the percentage of DMPG was increased. Using the Stern and Guoy-Chapman model, which takes into consideration electrostatic effects, we were able to simultaneously fit all our binding data with a minimum of fitting parameters. These parameters (for data at 45 degrees C) are an association constant, K, of 330 M-1, a maximum possible number of drug molecules absorbed per unit surface of vesicle, sigma m+, of 1.70 x 10(-2) A2, and a surface area per bound drug, gamma D, of 48 A2. The data were fitted equally well by an alternate model in which binding of the drug is described as a partitioning equilibrium, with factors included for electrostatic effects and surface expansion caused by drug intercalation between the fatty acid chains.

Association of spin-labeled local anesthetics at the hydrophobic surface of acetylcholine receptor in native membranes from Torpedo marmorata

The interactions between a series of spin-labeled local anesthetic analogues and the nicotinic acetylcholine receptor (AChR) have been investigated by means of electron spin resonance (ESR) and fluorescence spectroscopy. The paramagnetic local anesthetic analogues quenched the intrinsic tryptophan fluorescence of AChR-rich membranes in an agonist-dependent manner, demonstrating a direct interaction with the AChR. The quenching efficiency was greater for the benzocaine than for the thioprocaine analogue. The protein was found to restrict directly the molecular motion of the spin-labeled analogues, as seen by the appearance of a highly anisotropic component in the ESR spectrum. The relative affinity of the population of local anesthetic probes which interacts directly with the integral protein of the AChR-rich membranes was calculated on the basis of relative association constants, Kr, determined by ESR. By comparison with the relative association constant for spin-labeled phospholipid, Kro, it was possible to differentiate between local anesthetic analogues interacting with high (Kr/Kro greater than 2), intermediate (Kr/Kro = 1.6-1.9), and low (Kr/Kro less than or equal to 1.3) specificity and to calculate the fraction of protein-associated probe in each case. Differences were observed in the presence of agonist (0.1 mM carbamylcholine) with some, but not all, of the spin-labeled derivatives. The role of the protonatable diethylammonium group in the specificity of the interaction of the procaine and thioprocaine analogues was investigated. Only in the uncharged form, or in the charged form at high ionic strength, was there a preferential association of these two local anesthetic analogues.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of procaine on intracellular pH and its regulation: measurements with pH-selective micro-electrodes in Retzius neurones of the leech

The experiments were performed with double-barelled micro-electrodes in Retzius neurones of the leech in order to see if the tertiary amine local anesthetic procaine affects intracellular pH (pHi) and its regulation. Lasting about 20 min, exposures to procaine (3 mM) saline caused an intracellular alkalosis of about 0.2 pH units which gradually degradated; its removal initiated a fast decrease of pHi resulting in an acidosis, fron which the cells recovered. Detailed studies, involving CO2 or NH4+ acid loaded cells as well as inhibition of the pHi regulating exchange mechanism by various drugs or exposures to Na-free salines suggest, that neither the Na+ -H+, nor a probably Na+ -dependent HCO3-(-)Cl- exchange are affected by procaine. We propose a model for procaine action on pHi assuming that neutral procaine passes the membrane easily through lipophilic pathways. The degradation of alkalinity during procaine exposure hints on an entry of loaded procaine, some possible transport paths of which are discussed.

The effects of local anaesthetics on the electrical and mechanical activity of the guinea-pig ureter

The effects of local anaesthetic tertiary amines (procaine, lignocaine and tetracaine) as well as neutral (benzocaine) and permanently charged (QX-314) local anaesthetics were studied on the evoked electrical and mechanical activity of the ureter smooth muscle. 'Low' concentrations of procaine and lignocaine (0.1-1mM) at pH 7.4 increased the duration of the slow plateau component of the evoked action potentials. The amplitude of the phasic contraction was consequently increased within the first 5 min of exposure. Tetracaine 0.1 mM caused a transient increase in the duration of the plateau and amplitude of the phasic contraction within the first 1-2 min only. The stimulant action of the local anaesthetics was greatly reduced in the presence of tetraethylammonium (TEA). All the tertiary local anaesthetics caused depolarization of the membrane accompanied by an increase in the size of the electronic potentials. Lignocaine normally initiated the discharge of spontaneous action potentials. High concentrations of lignocaine (5 mM) and tetracaine (0.5 mM) caused complete inhibition of the evoked action potentials and phasic contractions. Procaine 5 mM predominantly inhibited the contractile responses. The permanently charged local anaesthetic QX-314 (1 mM) caused an increase in the duration and amplitude of the plateau, increasing the number of spikes and the amplitude and duration of the phasic contraction. It also depolarized the ureter smooth muscle cells increasing the size of electronic potentials. The neutral local anaesthetic benzocaine at 1 mM caused a reversible selective blockade of the plateau component of the evoked action potential and a gradual reduction in the amplitude of the phasic contraction. No change in either the membrane potential or the membrane conductance was observed. 7 High pH. (pH 9) significantly increased while low pH0 (pH 6) decreased the inhibitory action of procaine and lignocaine but did not alter the effects of benzocaine and QX-314. 8 Benzocaine caused a relaxation of the high-K-induced contraction, preferentially blocking the tonic component, whereas QX-314 had no effect on the KC1-contracture of the ureter muscle. 9 Two sites of action in the ureter smooth muscle cell membrane for local anaesthetics are suggested. One site interacts with local anaesthetics in a charged form, while the other one interacts with those in a lipid-soluble neutral form. The charged form of local anaesthetics has a TEA-like action, while the neutral form predominantly causes blockade of 'slow' Na/Ca channels.