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D E Raines

Publications and source records attributed to D E Raines.

27 records · Page 2Linked to original sources
PubMed1994

Lipid-protein interactions and protein dynamics in vesicles containing the nicotinic acetylcholine receptor: a study with ethanol.

Electron paramagnetic resonance (EPR) spectroscopy was used to study the action of ethanol on the protein side chain motions of the nicotinic acetylcholine receptor (nAcChoR) in alkaline extracted membranes from Torpedo nobiliana. EPR spectra of the nAcChoR derivatized with maleimide spin label contain both strongly and weakly immobilized components. The rotational correlation time of the strongly immobilized component decreases by a factor of 2-3-fold with the addition of 1.6 M ethanol, while that of the weakly immobilized component is not significantly altered. EPR spectroscopy was also used to probe the lipid environment immediately surrounding the nAcChoR with stearic acid and phosphatidylcholine spin labeled at the fourteenth acyl carbons (14-SASL and 14-PCSL, respectively), and the steroid spin label androstanol (ASL). EPR spectra of these probes reveal a component corresponding to lipids that are motionally restricted by the receptor (annular lipids) in addition to a more fluid component arising from bulk lipid. Using spectral subtraction, the order of selectivity of these spin labels for the nAcChoR was determined to be ASL > or = 14-SASL > 14-PCSL. The estimated rotational correlation times of the high affinity 14-SASL and ASL probes ranged from approx. 20 to 35 ns. The correlation times of the lower affinity 14-PCSL were generally shorter than those for 14-SASL and ASL and ranged from about 10 to 25 ns. The addition of up to 0.9 M ethanol altered neither the affinity nor the mobility of the motionally restricted EPR component. This suggests that ethanol's actions on the nAcChoR are not mediated via changes at the lipid/protein interface near the center of the bilayer.

Animals↗
PubMed1993

The effect of general anesthetics on the dynamics of phosphatidylcholine-acetylcholine receptor interactions in reconstituted vesicles.

The interaction of general anesthetics at the lipid/protein interface of the nicotinic acetylcholine receptor reconstituted in dioleoylphosphatidylcholine bilayers at various lipid/protein ratios has been studied using the electron spin resonance spectra of phosphatidylcholine spin-labeled at the fourteenth acyl carbon (14-PCSL). In addition to the bilayer spectrum, the spin label reported a more motionally restricted environment whose contribution increased with increasing protein/lipid ratio. Exchange between these two environments occurred at a rate of approx. 6 x 10(7) s-1. The motionally restricted, protein-associated 14-PCSL had a rotational correlation time of about 10-20 ns, an order of magnitude slower than when in the bilayer. Addition of 1-hexanol (up to 16 mM) to the reconstituted receptor perturbed the acyl chains of the bulk lipid phase, but the motional properties of the lipid acyl chains at the protein/lipid interface near the membrane center were not significantly perturbed on the EPR motional time-scale. Similarly, anesthetics that were less effective at perturbing the bilayer, such as pentobarbital (up to 2 mM) and isoflurane (7 mM), did not perturb the lipid/protein interface on the conventional EPR motional time scale.

Anesthesia, General↗
PubMed1993

The role of charge in lipid selectivity for the nicotinic acetylcholine receptor.

The effect of salt and pH titration on the selectivity of spin-labeled analogues of phosphatidic acid, phosphatidylserine, phosphatidylcholine, and stearic acid for the nicotinic acetylcholine receptor (nAcChoR) reconstituted into dioleoylphosphatidylcholine was examined at 0 degrees C using electron spin resonance spectroscopy. The order of selectivity at pH 7.4 and 0 mM NaCl was phosphatidylserine > stearic acid > phosphatidic acid > phosphatidylcholine. The addition up to 2 M NaCl or titration of pH from 5.0 to > 9.0 did not alter the selectivity of the phospholipids for the nAcChoR. For stearic acid, conversely, titration of pH from 5.0 to 9.0 at 0 mM NaCl and titration of NaCl from 0 to 2 M at pH 9.0 both increased selectivity for the nAcChoR. It is concluded that electrostatic interactions do not account for the selectivity of the negatively charged phospholipids, phosphatidylserine, and phosphatidic acid for the nAcChoR. This is consistent with the known orientation of the transmembrane sequences M1 and M4, which predicts a balance in the number of negative and positive charges in the lipid-protein interface and suggests that the two positive charges on each M3 helix are not exposed to the lipid-protein interface.

Animals↗
PubMed1993

Anesthetic cutoff in cycloalkanemethanols. A test of current theories.

BACKGROUND: N-alkanols containing up to 12 carbons are anesthetic; however, those with more than 12 carbons are not. This phenomenon has been termed cutoff. Lipid disordering theories of anesthesia suggest that cutoff occurs because the alkyl chains of long-chain alcohols approach the length and shape of the lipids of neuronal membranes and, therefore, intercalate into membranes without perturbing them. Protein theories suggest that cutoff occurs because the size of long-chain alcohols exceeds that of a protein binding site having finite dimensions. These theories were tested with a new series of alcohols, the cycloalkanemethanols, c(CnH2n-1).CH2.OH. METHODS: Anesthetic potency was measured in Rana pipiens tadpoles using the reversible loss of righting reflexes as the endpoint. The change in order parameter induced by cycloalkanemethanols and n-alkanols in lipid bilayers made of egg phosphatidylcholine and cholesterol was measured with electron paramagnetic resonance spectroscopy. RESULTS: On ascending the series from cyclopropanemethanol (EC50 = 54 +/- 3.2 mM) to cycloundecanemethanol (EC50 = 7.0 +/- 0.12 microM) anesthetic potencies first increased exponentially but then decreased sharply at cyclododecanemethanol (EC50 = 13 +/- 0.2 microM). Cyclotetradecanemethanol was found not to cause anesthesia in tadpoles, even after 48 h of exposure, although saturated solutions shifted the dose-response curve of octanol from 66 +/- 2.6 to 47 +/- 2.8 microM. A linear loss in the ability to disorder lipid bilayers was observed on ascending both alcohol series such that cyclotetradecanemethanol and n-tridecanol actually increased bilayer order. CONCLUSIONS: Molecular length does not correlate with anesthetic cutoff in these two alcohol series. Cutoff is predicted by the ability of both series of alcohols to disorder lipid bilayers and correlates with their molecular volume.

Anesthesia↗
PubMed1989

The enhancement of proton/hydroxyl flow across lipid vesicles by inhalation anesthetics.

When pH gradients are created across model lipid membranes, there is a well-documented electrogenic flow of protons, which results in the development of a transmembrane potential. As a result, protons come to electrochemical equilibrium across lipid vesicles within tens of minutes. The ability of a series of inhalation anesthetics to enhance the conduction of protons across model membranes was examined. When clinically relevant concentrations of halothane, isoflurane, enflurane, or chloroform were equilibrated with sonicated lipid vesicles, significant increases in the proton conduction were found. However, for even high anesthetic concentrations (above 8 MAC) of ether and cyclopropane, no increases in proton conduction could be detected. These results rule out a common mechanism for general anesthesia involving enhanced proton conduction across membranes.

Anesthesia, Inhalation↗
PubMed1987

Time-dependent binding of paramagnetic and fluorescent hydrophobic ions to the acetylcholine receptor from Torpedo.

In receptor-rich vesicles isolated from Torpedo, paramagnetic or fluorescent phosphonium ions bind to both the acetylcholine receptor (AcChR) and the receptor membrane. When added to receptor vesicles, two to three phosphoniums undergo a slow time-dependent binding to the AcChR. The presence of agonist increases the rate but not the extent of binding of the alkylphosphonium nitroxides. Approximately one phosphonium per receptor can be displaced by the addition of saturating concentrations of the high-affinity histrionicotoxin derivative isodihydrohistrionicotoxin or by the addition of phencyclidine or quinacrine mustard. In addition, preincubation of the receptor with these channel blockers prevents approximately one phosphonium from binding to the receptor. When a series of alkyltriphenylphosphonium ions was studied, it was found that the rate of phosphonium binding to the receptor decreased with increasing probe hydrophobicity. This appears to be a function of the partitioning of the probe between membrane and aqueous phases. The phosphonium ions used here promote desensitization of the receptor, as judged by the binding rate of the fluorescent agonist NBDA-C5-acylcholine or alpha-bungarotoxin. Preincubation of the receptor with isodihydrohistrionicotoxin virtually eliminates the phosphonium-mediated desensitization. The rates of the phosphonium-mediated desensitization also appear to be dependent upon the phase partitioning of the probe. These results strongly suggest that the binding sites for the phosphonium ion (and the high-affinity histrionicotoxin blocking site) are accessible only through the aqueous phase. The phosphonium binding and agonist-induced transitions observed here are not observed with a negative hydrophobic ion probe, or a negative surface amphiphile, indicating that modifications in membrane electrostatics do not contribute to the observed changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Potential-dependent phase partitioning of fluorescent hydrophobic ions in phospholipid vesicles.

Fluorescent, dansyl derivatives of triphenylalkylphosphonium ions have been synthesized and exhibit fluorescence intensities in small sonicated phospholipid vesicles that are dependent upon transmembrane potentials. The voltage-dependent fluorescence changes are a result of changes in quantum yield that accompany a voltage-dependent phase partitioning of the probe. This phase partitioning is easily quantitated by calibrating the intensities of totally membrane-associated and aqueous probe. The voltage-dependence is well accounted for by a simple thermodynamic model and allows an estimation of potentials from fluorescence intensities in small vesicle systems.

Dansyl Compounds↗