Role of energized states of (Na++K+)-ATPase in the sodium pump

Temperature-dependent nerve-blocking action of lidocaine and halothane

The effect of lidocaine and halothane on the compound action potential of rat sciatic nerves was studied under hypo-hyperthermic conditions. In drug-free desheathed nerves, a total but reversible cold block occurred at 10-11 degrees C, and an irreversible heat block at 46 degrees C. Cooling potentiated the dose-dependent blocking action of lidocaine (decreased amplitude, and increased duration and latency of the compound action potential). Total block of conduction occurred at 17 degrees C with 100 microM lidocaine, at 20 degrees C with 200 microM lidocaine and at 24 degrees microM with 400 microM lidocaine. In nerves equilibrated in 200 microM lidocaine solution, the lidocaine concentrations in the nerves decreased as the temperature decreased; at 20 degrees C, the lidocaine concentration was about half of that at 37 degrees C. The nerve-blocking effect of lidocaine was also potentiated by increasing the temperature above 37 degrees C. At 30 degrees C and 20 degrees C, 1 vol. % halothane caused a slight time-dependent inhibition of the compound action potential. When the nerves were exposed to 2.5 vol. % halothane, the decrease in amplitude and increase in duration and latency were potentiated by hypothermia and were also time dependent. Interaction of halothane and temperature of 40 degrees C was not significant. Although thermodynamic principles suggest similarities between high pressure and cooling in reversing anaesthesia, cooling was found to potentiate the anaesthetic effect of lidocaine and halothane in this study. Temperature may thus be an interesting physical variable in studying nerve-blocking mechanisms.

Temperature coefficients for the oxidative metabolic responses to electrical stimulation in cerebral cortex

Temperature coefficients of both cat and toad brain have been calculated for the active metabolic state induced by electrical stimulation. Values are higher than most of the values previously reported for "rest" metabolism, whether calculated from Arrhenius plots or from linear graphs. Relative rates of oxidative metabolism were obtained by measuring the time course of the transient changes in NADH fluorescence and cytochrome aa3 absorption by reflectance techniques directly from the surface of the exposed cat cerebral cortex in vivo and from the isolated intact toad brain mounted in a cuvet. These findings demonstrate that such optical methods accurately record metabolic processes.

Variation in sensitivity of the cardiac glycoside receptor characteristics of (Na+ + K+)-ATPase to lipolysis and temperature

1. The rate of binding of [3H]ouabain to untreated membrane preparations of [Na+ +K+]-ATPase is a timperature--dependent process displaying a thermal transition close to 25degreesC. The apparent energies of activation which can be calculated above and below this transition are similar to, but not identical with, those previously reported for activation of the enzyme by cations. 2. Treatment of the enzyme preparation with detergents or lipolysis with phospholipase A eliminates the thermal transition resulting in linear Arrhenius plots. 3. The number of sites available for [3H]ouabain binding is not temperature dependent as the amount of [3H]ouabain bound at equillbrium is not changed between 10 and 37 degrees C. 4. Treatment of the enzyme with phospholipase A results in time-dependent changes in the number of binding sites for [3H]ouabain at equilibrium. 5. Treatment of the membrane enzyme preparations with detergents reveals additional [3H]ouabain binding sites which are extremely sensitive to lipolysis with phospholipase A. 6. There are a number of [3H]ouabain binding sites which remain resistant to lipolysis by phospholipase A in either untreated or detergent-treated membrane preparations. 7. It is suggested that [3H]ouabain binding sites exist in the membrane in at least two different environments, one of which is resistant the other sensitive to attack by phopholipase A.

Endogenous oscillations in pathways of energy transduction as related to circadian rhythmicity and photoperiodic control

Evidence is presented for endogenous rhythmicity in energy transducing sequences of cellular metabolism which result in a circadian rhythm in adenylate "energy charge" and redox state (NADPH/NADP). From phase dependent photocontrol of enzymatic activity and pyridine nucleotide pool-size levels it is concluded that light - via photoreceptor(s) of photoperiodic control - modulates energy flow under conditions where overall energy transduction displays a circadian rhythm. The results are discussed in relation to temporal organization of development in general.

Isolation and characterization of the components of the sodium pump

A satisfactory understanding of the functions of the sodium pump, the system responsible for the active transport of sodium and potassium, require the isolation and characterization of its protein and lipid components which are integrated in the structure of the cell membrane. The enzyme system (Na++ K+)-ATPase, is located in membrane fragments and behaves in the test tube like the transport system in the intact cell membrane (Skou,1957) Purified preparations of this enzyme will contain some, if not all, of the components of the sodium pump.