Biomedical subjects

A H Delcour

Publications and source records attributed to A H Delcour.

25 records · Page 2Linked to original sources

PubMed1990

Ion channel activities in the Escherichia coli outer membrane.

The electrical properties of Escherichia coli cells were examined by the patch-clamp technique. Giant cells or giant spheroplasts were generated by five different methods. By electron micrographic and other criteria we determined that the patches are most likely from the outer membrane. We regularly observed currents through at least two types of channels in this membrane. The first current is mechanosensitive and voltage-dependent, and can be observed in single gene mutants of the known major porins (ompF, ompC, phoE, lamB); this channel may represent a minor porin or a new class of outer membrane protein. The possible identity of the second, voltage-sensitive channel with one of the known outer membrane proteins is being explored. The high-resistance seals consistently formed on these patches and the presence of gated ion channels suggest that most of the pores of the outer membrane are not statically open, as commonly held, but are closed at rest and may be openable by physiological stimuli.

Bacterial Outer Membrane Proteins↗

PubMed1989

Voltage-sensitive ion channel of Escherichia coli.

A voltage-sensitive, cation-selective ion channel of Escherichia coli has been reconstituted into liposomes and studied with the patch-clamp method. The single channel conductance was 91 pS in symmetric solutions of 150 mM KCl. Many channels were open most of the time, with frequent brief transitions to closed levels. Multiple conducting units could close and reopen simultaneously, and this apparent cooperativity in gating was increased with depolarizing voltages. Above a voltage threshold, the channels closed irreversibly, often in groups.

Bacterial Outer Membrane Proteins↗

PubMed1989

Modified reconstitution method used in patch-clamp studies of Escherichia coli ion channels.

We have modified the procedure of Criado and Keller (1987) to study ion channels of Escherichia coli reconstituted in liposomes. The modifications include (a) excluding the use of any detergent and (b) inducing blisters from liposomes with Mg2+. These blisters, which appear to be unilamellar, are stable for hours. They could be repeatedly sampled with different patch-clamp pipettes each achieving seal resistance greater than 10 GOhms. Activities of three types of ion channels are often observed by use of this method, including two voltage-sensitive cation channels of different conductances. Even the mechanosensitive channel, previously recorded from live E. coli cells (Martinac et al., 1987), was also detected in these blisters. Apparently the channel protein and any accessory structures, postulated to be needed for mechanotransduction, can be reconstituted together by this method.

Cell Membrane↗

PubMed1987

Pressure-sensitive ion channel in Escherichia coli.

We have used the patch-clamp electrical recording technique on giant spheroplasts of Escherichia coli and have discovered pressure-activated ion channels. The channels have the following properties: activation by slight positive or negative pressure; voltage dependence; large conductance; selectivity for anions over cations; dependence of activity on the species of permeant ions. We believe that these channels may be involved in bacterial osmoregulation and osmotaxis.

Electric Conductivity↗

PubMed1986

Chemical kinetic measurements of the effect of trans- and cis-3,3'-Bis[(trimethylammonio)methyl]azobenzene bromide on acetylcholine receptor mediated ion translocation in Electrophorus electricus and Torpedo californica.

A quench-flow technique was used to study the effect of trans- and cis-3,3'-bis[(trimethylammonio)methyl]azobenzene bromide (trans- and cis-Bis-Q), photoisomerizable ligands, on the acetylcholine receptor in vesicles prepared from the electric organ of Electrophorus electricus and of Torpedo californica. In E. electricus, two rate coefficients of the receptor-mediated translocation of 86Rb+ induced with trans-Bis-Q were measured: JA, the rate coefficient for ion flux, and alpha, the rate coefficient for receptor inactivation (desensitization). Both rate coefficients increase with increasing concentrations of Bis-Q up to 50 microM. At higher concentrations JA decreases in a concentration-dependent manner while alpha remains unchanged. This effect was previously observed with suberyldicholine [Pasquale, E. B., Takeyasu, K., Udgaonkar, J., Cash, D.J., Severski, M.C., & Hess, G. P. (1983) Biochemistry 22, 5967-5973] and with acetylcholine [Takeyasu, K., Udgaonkar, J., & Hess, G. P. (1983) Biochemistry 22, 5973-5978] and was analyzed in terms of a minimum mechanism that accounts for the properties of activation, desensitization, and inhibition of the receptor. Two molecules of trans-Bis-Q must be bound for the channel to open, but at concentrations greater than 50 microM the population of open channels decreases because of the additional binding of one molecule of trans-Bis-Q to a regulatory inhibitory site, independent of the activating sites. cis-Bis-Q does not induce transmembrane ion flux, but it does inhibit the response of the receptor to acetylcholine and induces inactivation (desensitization) in the micromolar range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Regulatory properties of acetylcholine receptor: evidence for two different inhibitory sites, one for acetylcholine and the other for a noncompetitive inhibitor of receptor function (procaine).

Does the acetylcholine receptor have a specific regulatory (inhibitory) site for the natural receptor ligand acetylcholine? This paper deals with this question. The inhibition of acetylcholine-receptor function by diverse organic cations including local anesthetics such as procaine has been well documented. Evidence indicates that these compounds are noncompetitive inhibitors, enter the open-channel form of the receptor, and block it and that the extent of this blockage depends on the transmembrane voltage of the cell. Recently we reported that in the electroplax of Electrophorus electricus the receptor-controlled transmembrane ion flux is inhibited by acetylcholine in a voltage-dependent, noncompetitive manner. We report here that the Torpedo californica receptor also has an inhibitory site for acetylcholine. The question of whether acetylcholine, which is an organic cation, binds to the same site as other organic cations such as the noncompetitive inhibitor procaine is important and is addressed. The results reported here of chemical kinetic investigations, with receptor-rich E. electricus and T. californica membrane vesicles, indicate that the inhibition of receptor function by acetylcholine and by a local anesthetic, procaine, involves two different receptor sites. The existence of a specific inhibitory site for the natural receptor-ligand acetylcholine suggests that this site can play an important role in the modulation of receptor function and in the regulation of transmission of signals between cells.

Acetylcholine↗

PubMedDate not supplied

Phosphorylation of the nicotinic acetylcholine receptor regulates its rate of desensitization.

Recent studies have provided evidence for a role of protein phosphorylation in the regulation of the function of various potassium and calcium channels (for reviews, see refs 1, 2). As these ion channels have not yet been isolated and characterized, it has not been possible to determine whether phosphorylation of the ion channels themselves alters their properties or whether some indirect mechanism is involved. In contrast, the nicotinic acetylcholine receptor, a neurotransmitter-dependent ion channel, has been extensively characterized biochemically and has been shown to be directly phosphorylated. The phosphorylation of this receptor is catalysed by at least three different protein kinases (cyclic AMP-dependent protein kinase, protein kinase C and a tyrosine-specific protein kinase) on seven different phosphorylation sites. However, the functional significance of phosphorylation of the receptor has been unclear. We have now examined the functional effects of phosphorylation of the nicotinic acetylcholine receptor by cAMP-dependent protein kinase. We investigated the ion transport properties of the purified and reconstituted acetylcholine receptor before and after phosphorylation. We report here that phosphorylation of the nicotinic acetylcholine receptor on the gamma- and delta-subunits by cAMP-dependent protein kinase increases the rate of the rapid desensitization of the receptor, a process by which the receptor is inactivated in the presence of acetylcholine (ACh). These results provide the first direct evidence that phosphorylation of an ion channel protein modulates its function and suggest that phosphorylation of postsynaptic receptors in general may play an important role in synaptic plasticity.

Acetylcholine↗