Inhibition of ATPase activity in human red cell membranes by tetracaine

Effect of positively charged local anesthetics on a membrane-bound phosphatase in Acholeplasma laidlawii

The plasma membrane p-nitrophenylphosphatase activity of Acholeplasma laidlawii was stimulated by the spin-labeled local anesthetic 2-[N-methyl-N-(2,2,6,6-tetramethylpiperidinooxyl)]ethyl p-hexyloxybenzoate, abbreviated as C6SL, and its methylated quaternary analog, C6SLMeI. The tertiary amine C6SL (at a concentration of 5 X 10(-5) M) was more potent at pH 6.5 than at pH 7.7. In contrast, the permanently-charged C6SLMeI was equally potent, independently of pH. These results suggest that cationic forms of the anesthetics are responsible for stimulating the enzyme. Electron spin resonance studies of C6SL- and C6SLMeI-labeled membranes showed that these anesthetics in their cationic forms interacted electrostatically with components of the Acholeplasma membrane. For C6SL, this interaction was pH dependent and correlated with the pH dependency of the anesthetic-induced enzyme stimulation in the Acholeplasma membranes. Further, studies using 5-doxylstearic acid labels and non-spin-labeled anesthetics at various pH values showed that the membrane-fluidizing effect of anesthetics was not correlated with anesthetic-induced pNPPase stimulation. Our observations are consistent with the hypothesis that electrostatic interactions between cationic local anesthetics and anionic membrane components may lead to functional changes mediated by membrane proteins.

Inhibition of dog kidney Na+, K+-ATPase activity by procaine, tetracaine and dibucaine

The potency of local anesthetics as inhibitors of Na+, K+-ATPase and K+- NPPase activities correlated with lipid solubility. The order of potencies was: dibucaine greater than tetracaine much greater than procaine. Na+-ATPase activity was remarkably more sensitive to inhibition by tetracaine and procaine, and inhibitory potency did not correlate with lipid solubility. The order of potencies for inhibition of Na+-ATPase activity was: tetracaine greater than dibucaine greater than procaine. We examined interactions between the local anesthetics and monovalent cations in an attempt to explain this observation. Inhibition of Na+-K+-ATPase by tetracaine and dibucaine was competitive with respect to Na+, and inhibition of Na+-ATPase activity by all three agents was competitive with respect to Na+. Inhibition of Na+, K+-ATPase activity by procaine and tetracaine was competitive with respect to K+, and inhibition of K+- NPPase activity by all three agents was competitive with respect to K+. Dibucaine, the most lipid soluble agent, was equipotent as an inhibitor of all three activities and was generally less effective as a competitor with respect to activation by monovalent cations. These results suggest that dibucaine may interact nonspecifically with membrane lipids to inhibit enzyme activity whereas less lipid soluble agents, such as tetracaine and procaine, may interact more selectively with cation binding sites. It appears that the presence of K+ in the assay medium specifically decreases the inhibitory potency of tetracaine and procaine. Direct competition between these agents and K+ may prevent inhibition or, alternately, the presence of K+ may convert the enzyme to a conformation less susceptible to inhibition by agents of low to intermediate lipid solubility.

Chloral hydrate inhibition in vitro of ATPase in membrane of rat erythrocytes and in microsomes of dog kidney external medulla

The study of the general anesthetic chloral hydrate and its effects on rat erythrocyte membranes and dog kidney microsomes showed that ATPases were reversibly inhibited in every case. The inhibition was cooperative in the cases of (Mg2+ + Na+ + K+)-ATPase, Mg2+-ATPase and (Na+ + K+)-ATPase of rat erythrocyte membrane, while Ca2+-ATPase and (Mg2+ + Ca2+)-ATPase were non-cooperative. The chloral hydrate concentrations necessary to diminish the activity of the enzyme to half of the Vmax (I50) were 6 mM for Ca2+-ATPase from erythrocyte membranes and 82 mM for Mg2+-ATPase from intact external kidney medulla microsomes. When Ca2+-ATPase was studied in the absence of Mg2+ in these microsomes, the affinity for Ca2+ was very low, but the enzyme was sensitive to chloral hydrate.

Local anesthetic-membrane interaction: a multiequilibrium model

We report the detection of electrostatic interactions between local anesthetics and membrane phospholipids and proteins. A spin-labeled local anesthetic was used to study how membrane-bound tertiary amine anesthetics interact with major molecular components in the membrane. The nitroxyl reporter group of this spin label is located at the polar end of the amphiphilic local anesthetic; it is therefore a uniquely suitable probe for detecting immobilization of the anesthetic due to binding interactions at the polar regions of the bilayer. The binding properties of this spin-labeled anesthetic to human erythrocyte membranes and to vesicles made from human erythrocyte lipids were studied. Lipid vesicle-bound spin labels give rise to a composite electron spin resonance spectrum from which two subcomponent spectra were resolved. Both components are membrane-bound; the first component has a narrower linewidth, indicating a greater mobility of the nitroxyl moiety of the anesthetic probe. The second component has a broader linewidth, indicating a population of constrained spin labels. We infer from the experimental results that electrostatic binding between cationic anesthetics and anionic phosphate of phospholipids produced the constrained component. In similar studies using erythrocyte ghost membranes, both a mobile (nonelectrostatic) component and a constrained (electrostatic) component were resolved from the composite spectrum. However, the constrained component in this case is much broader than the corresponding constrained component from the vesicles. We interpret this broad component in the erythrocyte membrane as an electrostatic interaction of cationic anesthetic probes with phospholipids and with membrane proteins. We conclude that membrane-bound tertiary amine anesthetics in cationic form do interact selectively with phospholipids and proteins.

Different concentrations of local anaesthetics have different modes of action on human lymphocytes

Lidocaine and Bupivacaine inhibit in vitro 3H-TdR incorporation into peripheral lymphocytes, in a dose dependent ratio, either under PHA stimulus or not. Lidocaine added to cultures at various times from PHA stimulus show a reduced inhibition only when added after the 24th hour. This suggests a sensitizing action of PHA. Lidocaine effect on mitosis of doses between 2000 and 500 micrograms/ml was not completely reversible even when the drug was removed after only 15 min; between 200 and 50 micrograms/ml this effect is reversible. Lymphocyte viability by Trypan Blue exclusion is clearly unrelated to mitotic inhibition; it is however dose related. High Lidocaine and Bupivacaine concentration alter adhesion of cells to plastics and decrease lymphocyte aggregation by PHA. Electrophoretic mobility of lymphocytes incubated with 2000 micrograms/ml of Lidocaine is slower compared to controls; there is no change at 200 micrograms/ml. Local anaesthetics modify steric membrane structure reducing surface charge density. Increased Ca++ in the medium containing local anaesthetic increases lymphocyte stimulation index slightly only for Lidocaine and Bupivacaine doses, which neither alter membrane function nor interfere with lymphocyte viability nor electrophoretic mobility. Increased Na+ and K+ in the medium do not affect local anaesthetic action.

Local anesthetics, mepacrine, and propranolol are antagonists of calmodulin

Local anesthetics such as dibucaine, QX572, tetracaine, and phenacaine, as well as other drugs with local anesthetic-like properties (e.g., mepacrine, propranolol, and SKF 525A) inhibit the specific calmodulin-dependent stimulation of erythrocyte Ca2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and cyclic nucleotide phosphodiesterases (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) from brain and heart. Basal activities of these enzymes in the absence of calmodulin are relatively unaffected by concentrations of local anesthetics that strongly inhibit the specific stimulation by calmodulin. Increasing calmodulin, but not Ca2+, overcomes the inhibitory action of the local anesthetics on brain phosphodiesterase. However, excess calmodulin does not fully restore activity of erythrocyte CA2+-stimulated ATPase. Although the mechanism(s) by which the local anesthetics act is unclear, they inhibit binding of 125I-labeled calmodulin to the erythrocyte membrane. Antagonism of calmodulin provides a molecular mechanism that may explain the inhibition of many Ca2+-dependent cellular processes by local anesthetics--e.g., Ca2+ transport, exocytosis, excitation-contraction coupling, non-muscle-cell motility, and aggregation.