Biomedical subjects

B Rehberg

Publications and source records attributed to B Rehberg.

25 records · Page 2Linked to original sources

PubMed1997

No evidence for specific opioid effects on batrachotoxin-modified sodium channels from human brain synaptosomes.

Human central nervous system (CNS) sodium channels modified by batrachotoxin and incorporated inter voltage-clamped lipid bilayers, were exposed to various concentrations of the opioid alfentanil (0.2-8.0 mM). Alfentanil caused a concentration-dependent and membrane potential independent reduction of the single channel amplitude and the fractional channel open-time. The weighted computer fit of the dose-response curve yielded a maximal conductance block of 50% with an EC50 of 1.3 mM. These effects occurred at levels beyond clinically relevant human serum/brain levels (0.003 mM) but within the predicted concentration range using the Meyer-Overton (lipid solubility/anaesthetic potency) correlation. Thus, human CNS sodium channels are probably not a main target site for the clinical effects of alfentanil but they provide a model system to estimate the proportion of the lipophilic interactions contributing to its overall effect.

Alfentanil↗

PubMed1996

Central nervous system sodium channels are significantly suppressed at clinical concentrations of volatile anesthetics.

BACKGROUND: Although voltage-dependent sodium channels have been proposed as possible molecular sites of anesthetic action, they generally are considered too insensitive to be likely molecular targets. However, most previous molecular studies have used peripheral sodium channels as models. To examine the interactions of volatile anesthetics with mammalian central nervous system voltage-gated sodium channels, rat brain IIA sodium channels were expressed in a stably transfected Chinese hamster ovary cell line, and their modification by volatile anesthetics was examined. METHODS: Sodium currents were measured using whole cell patch clamp recordings. Test solutions were equilibrated with the test anesthetics and perfused externally on the cells. Anesthetic concentrations in the perfusion solution were determined by gas chromatography. RESULTS: All anesthetics significantly suppressed sodium currents at clinical concentrations. This suppression occurred through at least two mechanisms: (1) a potential-independent suppression of resting or open sodium channels, and (2) a hyperpolarizing shift in the voltage-dependence of channel inactivation resulting in a potential-dependent suppression of sodium currents. The voltage-dependent interaction results in IC50 values for anesthetic suppression of sodium channels that are close to clinical concentrations at potentials near the resting membrane potential.

Anesthetics, Inhalation↗

PubMed1995

[Do general anesthetics act on specific receptors?].

First of all, the meanings of the terms anaesthesia, anaesthetic and receptor are defined. Examples of anaesthetic actions in model systems are then described and compared with clinical actions of anaesthetics. When anaesthetics achieve a certain membrane concentration, they begin to influence membrane protein function in a nonspecific manner. If the anaesthetic drug possesses polar functional groups in addition to lipophilic ones, it may selectively affect membrane proteins and interact with them specifically. The absolute lipophilicity of a drug does not necessarily determine whether or not a drug is a suitable anaesthetic. Rather, it is important that the drug does not show undesirable side effects when it achieves a critical membrane concentration at which lipophilic interactions occur. There are examples of specific interactions of general anaesthetics with receptors as well as examples of nonspecific effects on membranes. Whether these interactions are important for anaesthesia remains to be seen.

Anesthesia, General↗

PubMed1995

The membrane lipid cholesterol modulates anesthetic actions on a human brain ion channel.

BACKGROUND: Molecular theories of general anesthesia often are divided into two categories: (1) Anesthetics may bind specifically to proteins, such as ionic channels, and alter their function directly, and (2) anesthetics may alter the functions of integral membrane proteins indirectly through modification of the physical properties of the membrane. Recent studies have provided evidence that anesthetics can bind to proteins and modify their function directly, bringing into question the role of the membrane in anesthetic interactions. To reexamine the role of membrane lipids in anesthetic interactions, an experimental approach was used in which the membrane lipid composition could be systematically altered and the impact on anesthetic interactions with potential targets examined. METHODS: Sodium channels from human brain cortex were incorporated into planar lipid bilayers with increasing cholesterol content. The anesthetic suppression of these channels by pentobarbital was quantitatively examined by single channel measurements under voltage-clamp conditions. RESULTS: Changes in cholesterol content had no effect on measured channel properties in the absence of anesthetic. In the presence of pentobarbital, however, cholesterol inhibited anesthetic suppression of channel ionic currents, with 1.9% (weight/weight, corresponding to 3.5 mol%) cholesterol decreasing anesthetic suppression of sodium channels by half. CONCLUSIONS: These results support a critical role for the lipid membrane in some anesthetic actions and further indicate that differences in lipid composition must be considered in the interpretation of results when comparing the anesthetic potencies of potential targets in model systems.

Cerebral Cortex↗

PubMed1995

Voltage- and frequency-dependent pentobarbital suppression of brain and muscle sodium channels expressed in a mammalian cell line.

The voltage- and frequency-dependent interactions of pentobarbital with voltage-gated sodium channels were examined in whole-cell patch-clamp recordings. Using rat brain IIA and rat muscle rSkM1 sodium channels expressed in stably transfected Chinese hamster ovary cell lines, it was found that pentobarbital reduced peak inward sodium currents with IC50 values of 1.2 mM (brain) and 1.0 mM (muscle). Analysis of steady state channel availability curves revealed two distinct effects of pentobarbital on both channel isoforms, i.e., a voltage-independent current reduction and an additional hyperpolarizing shift in the voltage dependence of channel availability. The latter effect leads to a voltage dependence of pentobarbital potency. Pentobarbital was also found to slow channel recovery after depolarization, yielding an additional use-dependent component of current suppression. Use-dependent block was enhanced by higher stimulation frequencies, longer pulse durations, and more depolarized holding and pulse potentials. All effects were identical for both channels. These findings can be explained in terms of the modulated receptor hypothesis and are consistent with a preferential interaction of pentobarbital with the inactivated channel state. As a consequence, actual pentobarbital potency would depend largely on experimental conditions or, in vivo, on the physiological parameters of a particular cell.

Animals↗

PubMed1994

The voltage-dependent action of pentobarbital on batrachotoxin-modified human brain sodium channels.

The voltage-dependent action of the intravenous anesthetic pentobarbital on human brain sodium channels activated by batrachotoxin was examined using planar lipid bilayer methods. Fractional open time-data were fitted by Boltzmann functions to yield simple parameters characterizing the voltage-dependence of the fractional open time. Pentobarbital caused a dose-dependent reduction of the maximum fractional open time of the sodium channel and a shift of the potential of half-maximal open time towards hyperpolarized potentials, whereas the slope parameter of the Boltzmann-fits was unaffected. A statistically significant increase of the variability of these parameters was found only in the case of the maximum fractional open time, indicating a random fluctuation of pentobarbital-induced suppression of the sodium channels over time. The voltage-dependent action of pentobarbital probably results from either a pentobarbital-modification of channel activation gating and/or a modification of the pentobarbital action by the gating process itself.

Batrachotoxins↗

PubMed1994

Molecular actions of pentobarbitone on sodium channels in lipid bilayers: role of channel structure.

The molecular mechanisms by which anaesthetics interfere with neuronal function are controversial. We have examined the effects of pentobarbitone on muscle-derived (eel electroplax) sodium channels incorporated into planar bilayers under exactly the same experimental conditions that we used previously to study the anaesthetic modification of human brain channels. This technique allows examination of protein-mediated similarities and differences. Sodium channels from the electroplax (muscle-derived) of the electric eel were purified and reconstituted into planar lipid bilayers containing 4:1 phosphatidylethanolamine:phosphatidylcholine in the presence of batrachotoxin, a sodium channel activator. Pentobarbitone had similar voltage-independent blocking effects on sodium channels from eel electroplax and human brain, as demonstrated by similar dose-response curves (IC50 = 613 mumol litre-1). However, activation of sodium channels from eel electroplax, in contrast with human brain, was relatively insensitive to the concentration of pentobarbitone. The only significant effect was a -5.8-mV shift in the activation midpoint with pentobarbitone 680 mumol litre-1. Therefore, differences in primary structures played no role in the observed voltage-independent block of channels by pentobarbitone, whereas subunits or other structural differences between sodium channels from eel electroplax and human brain must be responsible for the minimal effect of pentobarbitone on activation of muscle-derived sodium channels.

Action Potentials↗