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J S Bramhall

Publications and source records attributed to J S Bramhall.

9 recordsLinked to original sources
PubMed1989

Amphotericin B-induced changes in renal membrane permeation: a model of nephrotoxicity.

As part of an investigation into the nephrotoxic effects of the polyene antibiotic Amphotericin B we have studied its effects on the ion permeability of purified renal brush border membrane vesicles. Membrane potentials were measured using a potential sensitive carbocyanine dye, and ion permeabilities were calculated from the constant field equation. Amphotericin B significantly altered the ionic permeability sequence of isolated membranes and caused a selectivity for increasing the permeation of anions. Permeability changes induced by 2.0 micrograms/ml Amphotericin B resulted in an estimated hyperpolarization of the membrane from -50 mV to -72 mV. In addition, the kinetic parameters of Na+ dependent transport of organic metabolites were examined. The maximum change in fluorescence was decreased significantly in the presence of Amphotericin B. These results suggest that the ionic state of the renal cell membrane is significantly altered by the presence of Amphotericin B.

Amphotericin B↗
PubMed1981

Photolabelling of cholera toxin subunits during membrane penetration.

There has been much speculation about the mechanism by which cholera toxin exerts its effect on the cytoplasmic side of the membranes with which it interacts. After the pentamer of B subunits (5B) binds to membrane receptors, particularly the monosialylganglioside GM1, the disulphide-linked dimer A1SSA2 (which together with 5B constitutes the complete toxin) is thought to penetrate the membrane, perhaps through a channel formed by 5B and become reduced so that A1SH units reach the cytoplasm and stimulate adenylate cyclase. Evidence for this mechanism is circumstantial. If it is correct, a compound which will specifically label intramembranous sections of the toxin should label the channel-forming B subunits but not the channel-contained A1 subunit. We have tested this prediction with a photoreactive glycolipid compound and have obtained the opposite result. Therefore, we propose that only the A1 subunit enters the membrane and we provide here data on the kinetics of that process.

Cholera Toxin↗
PubMed1979

Analysis of transmembrane dynamics of cholera toxin using photoreactive probes.

Using sodium dodecyl sulfate--polyacrylamide gel electrophoresis and autoradiography, we have shown that 125I-labeled cholera toxin binds to Newcastle disease virus. Pretreatment of Newcastle disease virus with "cold" cholera toxin (at 37 degrees C for 30 minutes) inhibits the binding of 125I-labeled toxin in a subsequent incubation (at 37 degrees C for 30 minutes). These results suggest that cholera toxin binds to Newcastle disease virus in a specific manner. The precise receptor for toxin is unknown in Newcastle disease virus but it is presumed to be the ganglioside GM1. We have previously shown that the photoreactive probe 12-(4-azido-2-nitrophenoxy)stearoylglucosamine[1-14C] labels the membrane proteins of Newcastle disease virus. Since the reactive group of the probe, ie, N3, resides within the membrane bilayer, studies were initiated to determined which, if any, of the subunits of cholera toxin cross the membrane of Newcastle disease virus and become radioactively labeled upon photoactivation of the probe at 360 nm. After a 15-minute incubation of cholera toxin with Newcastle disease virus containing the photoreactive probe, irradiation effected the 14C-labeling of the active A1 subunit of cholera toxin. Irradiation of cholera toxin in solution with an equivalent amount of probe but without virus resulted in no labeling of toxin subunits.

Azides↗