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B S Hill

Publications and source records attributed to B S Hill.

11 recordsLinked to original sources
PubMed1988

Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase.

Previous studies have shown that acetaminophen (APAP) is converted by prostaglandin H synthase (PGHS) to both one-electron oxidized products and the two-electron oxidized product, N-acetyl-p-benzoquinone imine (NAPQI). The present study further characterizes this reaction and shows that relatively low concentrations (20-200 microM) of APAP stimulate PGHS activity in ram seminal vesicle microsomes, whereas high concentrations (greater than 10 mM) inhibit the conversion of arachidonic acid (AA) to 15-hydroperoxy-9,11-peroxidoprosta-5,13-dienoic acid (PGG2). Stimulatory and inhibitory activities apparently involve the reduction of oxidized complexes of PGHS, and stimulatory and inhibitory activities roughly correlate with the electrochemical half-wave oxidation potentials of a series of hydroxyacetanilides. Using APAP as a probe, it was found that at low concentrations, APAP is converted in a cooxidation reaction with arachidonic acid to a dimer, 4'4"'-dihydroxy-3', 3"'-biacetanilide (bi-APAP), and other polymeric products. Moreover, an electrophilic metabolite of acetaminophen, NAPQI, was detected directly and also detected indirectly by its reaction with glutathione (GSH) to form 3'-(S-glutathionyl)acetaminophen (GS-APAP). The formation of all products was inhibited by indomethacin and the reductants, ascorbic acid and butylated hydroxyanisole (BHA). However, in the presence of GSH, ascorbic acid only partially inhibited the formation of GS-APAP while almost completely inhibiting the formation of bi-APAP. The same products of APAP (bi-APAP and NAPQI) were formed by PGHS and hydrogen peroxide in reactions that were not inhibited by indomethacin. At high concentrations of APAP that inhibit PGHS, the formation of products in the presence of arachidonic acid but not H2O2 was inhibited. These findings are generally consistent with a mechanism of acetaminophen oxidation by PGHS that involves common intermediate enzyme forms for both cyclooxygenase- and hydroperoxidase-catalyzed reactions. At least one of the intermediate complexes is reduced by relatively low concentrations of APAP and stimulates PGHS, whereas another intermediate complex is reduced by APAP at higher concentrations to inhibit the enzyme.

Acetaminophen↗
PubMed1987

Steady-state analysis of ion fluxes in Necturus gall-bladder epithelial cells.

1. The steady-state fluxes of Na, K and Cl ions have been measured in Necturus gall-bladder epithelium by a technique that involves labelling the cells with tracer ions from the mucosal bath only, whilst the serosa is kept at low specific activity. After removing tracer, the efflux is followed into the serosal bath, revealing two exponential components. 2. The time constant of the fast component lies between 0.03 and 0.04 s-1 and corresponds to that of the extracellular space. The slow component closely matches the cellular efflux, with constants which lie between 0.14 and 0.46 X 10(-2) s-1. 3. Full unstirred-layer calculations have been performed to determine the specific activities in the mucosal solution, the cell and the corium (subepithelium). These involved measuring the diffusion coefficients of Na and Cl in the isolated corium: they are restricted by factors of 0.17 and 0.11. 4. The partial flux equations for this double-membrane system have been solved to obtain the cellular fluxes for all three ions. The results indicate that: (i) the net transcellular Na flux is 190 pmol cm-2 s-1, equivalent to the transepithelial salt flux during fluid secretion; (ii) the net transcellular K flux is effectively zero because this ion recirculates across the serosal membrane; (iii) the net transcellular Cl flux is 27 pmol cm-2 s-1, or 15% of the net transepithelial salt flux. 5. The permeability of the paracellular pathway to Cl is 1.65 X 10(-5) cm s-1 and the available driving forces will allow a maximum net electrodiffusive Cl transport of 10% through the shunt pathway. 6. 1:1 coupling of Na and Cl net fluxes at the mucosal membrane of this epithelium cannot be present, and processes other than simple electrodiffussion are required to effect net Cl transport by another route. 7. The serosal fluxes of K and Cl do not obey the flux-ratio equation. A component of these fluxes must be present which is neither active (pumped) nor passive (electrodiffusive and independent). If they are symmetrical in the steady state then the ratio of these exchange fluxes lies between 2:1 and 3:1 depending upon the size of the pump flux. They support the view that a mode of coupled K and Cl transport may be operating at the basolateral membrane of these cells.

Animals↗
PubMed1987

Transcellular sodium fluxes and pump activity in Necturus gall-bladder epithelial cells.

1. Transepithelial Na transport in Necturus was determined by measuring the rate of isotonic fluid flow. The rate at 20 degrees C was equivalent to 175 pmol cm-2 s-1. 2. Ouabain was effective in Necturus, binding to the Na pump in gall-bladder cells with a mean rate constant of 5.4 X 10(3) M-1 s-1. Measurement of the diffusive time constant of the free space for [3H]ouabain shows that the pump must be fully inhibited within 20 s when ouabain is applied to the serosa at 10(-3) M. 3. The serosal Na efflux from loaded cells was inhibited 36% by ouabain equal to a flux of 73 pmol cm-2 s-1. The remaining flux could not be attributed to either exchange diffusion or electrodiffusion induced by ouabain. 4. The transepithelial potential was 0.3 mV serosa positive. The short-circuit current measured was 6.33 +/- 1.9 microA cm-2, equal to a positive univalent ion flux of 65.6 pmol cm-2 s-1 or 38% of the net Na transfer. The current was inhibited within 1-5 min by 5 X 10(-5) M-amiloride. 5. Fluid secretion was immediately inhibited 34% by ouabain, equivalent to an isotonic transport of Na of 59.7 pmol cm-2 s-1. Thereafter it continued for at least an hour, sometimes declining slowly. Amiloride had little effect (13%). 6. The Na pump rate was measured by titrating the cell content with tracer Na at different times after ouabain treatment. The initial slope was equal to a rate of 61.6 pmol cm-2 s-1 or 35% of the net flux at time zero. 7. The Na pump rate has also been measured by recording the rise in cell Na activity with ion-specific micro-electrodes, and correcting for swelling effects. The Na pump rate was very similar to that estimated from the rise in tracer Na content, equal to 59.3 pmol cm-2 s-1 or 31.4% of the transepithelial rate. Examination of the same experiment in the literature shows a closely similar value, about one-third of that expected from fluid secretion or net flux measurements. 8. A scheme is proposed to explain the results, which requires a flow of NaCl through a parallel pathway of small Na content involving exchange en route with the cytoplasmic Na.

Action Potentials↗
PubMed1978

Chloride dependence of active sodium transport in frog skin: the role of intercellular spaces.

1. In agreement with previous observations the replacement of Cl by a nonpenetrating anion in the solution bathing either the outside or both sides of the frog skin causes a fall in the short-circuit current. 2. When Cl is replaced by a non-penetrating anion in the solution bathing the outside of the frog skin the Isc is still a correct measure of the net Na transport. 3. Under the same conditions both active and shunt paths seem to be affected since there is a decrease in Isc, Na influx, amiloride-dependent conductance, and initial Na uptake across the external barrier, together with a decrease in Cl-backfluxes and amiloride-independent conductance. There is also a decrease in water permeability and a reduction in size of the intercellular spaces. 4. The removal of Cl does not appear to affect the entry step of Na but may have an effect on the shunt path. This in turn may change the active Na transport.

Animals↗