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Biomedical subjects

A G Lowe

Publications and source records attributed to A G Lowe.

31 records · Page 2Linked to original sources
PubMed1980

Chloride-bicarbonate exchange in human red cells measured using a stopped flow apparatus.

1. A new stopped-flow apparatus has been used to measure the exchange of intracellular chloride and extracellular bicarbonate across the human erythrocyte membrane at 37 degrees C. 2. The concentration dependence of the activation of the anion exchange system by extracellular bicarbonate was consistent with the existence of a saturable membrane-carrier. Analysis of the results assuming Michaelis--Menten kinetics indicated a Vmax for chloride--bicarbonate exchange of 73 . 4 +/- 14 . 4 mol. (3 x 10(13) cells.min)-1 and Km for bicarbonate of 11 . 1 +/- 2 . 8 mM at 37 degrees C (pH 7 . 1). 3. Correction of the directly computed values of Vmax for incomplete saturation of the carrier by intracellular chloride and the inhibitory effects of intracellular bicarbonate and extracellular chloride gave a Vmax of 157 +/- 43 . 8 mol (3 x 10(13) cells.min)-1 and a Km of 15 . 5 +/- 5 . 2 mM-bicarbonate at 37 degrees C. 4. Comparison of Vmax obtained at 37 and 10 degrees C indicates that the activation energy for chloride--bicarbonate exchange in this temperature range is 18 . 7 --19 . 6 kcal.mol-1 depending on whether corrected or uncorrected values are used. 5. Extracellular furosemide inhibited chloride--bicarbonate exchange with a KI of 0 . 12 microM assuming competition between furosemide and bicarbonate and 0 . 17 microM assuming non-competitive inhibition. 6. Extracellular chloride also inhibited chloride--bicarbonate exchange but the kinetics of inhibition were complex.

Bicarbonates↗
PubMed1980

Effect of prostaglandin inhibition on demeclocycline administration in conscious rats.

Studies were performed in conscious rats to evaluate the role of renal prostaglandin biosynthesis in demeclocycline-induced polyuria. Three groups of animals were evaluated. Group 1 animals received only the diluents used for both demeclocycline and indomethacin. Group 2 received demeclocycline (20 mg/kg/day) and the indomethacin diluent. Group 3 received both demeclocycline and indomethacin (10 mg/kg/day). After eight days of demeclocycline administration, urine flow rate increased in the group 2 animals from 15.1 +/- 2.1 to 31.1 +/- 5.1 ml/day. Indomethacin failed to alter the magnitude of demeclocycline-induced polyuria despite a 60% reduction in urine prostaglandin E excretion rats. These studies demonstrate that the concentrating defect induced by demeclocycline can occur independent of alterations in praostaglandin biosynthesis and suggest that a change in renal prostaglandin biosynthesis is not an etiologic factor in demeclocycline-induced polyuria.

Animals↗
PubMed1978

Chloride/bicarbonate exchange in human erythrocytes.

1. The exchange of chloride and bicarbonate across the human erythrocyte membrane has been followed by measuring the changes in extracellular pH which occur when chloride-rich erythrocytes are added to chloride-free media containing varying concentrations of bicarbonate and carbonic anhydrase. 2. The dependence of the rate of chloride/bicarbonate exchange on the extracellular concentration of bicarbonate was consistent with the existence of a saturable membrane anion transporter exhibiting Michaelis--Menten kinetics. In a medium containing sodium gluconate buffered to pH 7.0 with imidazole--malate the Km for bicarbonate activation of transport was 0.39 (+/- 0.03) mM and the Vmax was 2033 (+/- 80 m-mole anions exchanged/3 X 10(13) cells. min, at 10 degrees C. 3. Chloride/bicarbonate exchange was temperature-dependent with an Arrhenius activation energy of 19.4 kcal/mole in the temperature range 2--10 degrees C. 4. Exchange of intracellular chloride for extracellular bicarbonate was inhibited by the presence of extracellular halides. Inhibition by chloride, bromide and fluoride was competitive and the affinity of the transport system decreased in the order HCO-3 greater than Cl- greater than Br- greater than F-. The kinetics of inhibition by iodide were complex, but inhibitory effects of low concentrations of iodide were less than those of chloride and bromide.

Bicarbonates↗
PubMed1977

The pre-steady-state hydrolysis of ATP by porcine brain (Na+ + K+)-dependent ATPase.

The hydrolysis of [gamma-32P]ATP by porcine brain (Na+ + K+)-stimulated ATP phosphohydrolase (EC 3.6.1.3) has been studied at 28 degree C in a rapid mixing quenched-flow apparatus. An "early burst" in the release of Pi from ATP has been observed when the enzyme is mixed with ATP, Na+ and a relatively high concentration of K+ (10 mM) but the burst is less pronounced with 0.5 mM K+. This "early burst" of Pi release is suppressed when the enzyme is pre-mixed with 10 mM K+ or 20% (v/v) dimethylsulphoxide before mixing with ATP and Na+, and premixing of enzyme with Na+ antagonizes this effect of dimethylsulphoxide. The results have been analysed by a non-linear least squares regression treatment and are consistent with a mechanism involving three steps, one of which may be a relatively slow change in enzyme conformation following release of Pi from its covalent linkage with the enzyme, in addition to formation of the enzyme-substrate complex. Rate constants (and S.E.) for these steps have been calculated and the roles of phospho-enzyme and other intermediates in the reaction mechanism of the transport ATPase are dicussed.

Adenosine Triphosphatases↗
PubMed1972

The efflux of calcium from single crab and barnacle muscle fibres.

1. The efflux of calcium, as the isotope (45)Ca, has been investigated from single muscle fibres from the barnacle Balanus nubilus and from the crab Maia squinado.2. If the isotope was initially injected with sufficient calcium (5-65 mM) to cause a contraction, the efflux did not follow first order kinetics. There was an early rapid phase which reached a peak after 5-10 min and then declined slowly over a period of 50-150 min to a low residual value.3. Injection of the isotope with the calcium-binding agent EGTA, so that the injected free calcium concentration was ca. 2 x 10(-8)M, abolished the initial rapid loss of calcium. The efflux rose to give a steady value after 10-15 min and its magnitude was similar to the value of the residual efflux.4. The rate constant for the low residual loss was ca. 7 x 10(-4) min(-1) for Maia and ca. 17 x 10(-4) min(-1) for Balanus. The rate constant predicted a calcium efflux of 0.4 p-mole/cm(2).sec for Maia and 1-2 p-mole/cm(2).sec for Balanus at 16-25 degrees C based on the total fibre calcium concentration.5. The residual calcium efflux was not affected by 0.5 mM ouabain or 0 potassium salines applied externally. It was stimulated, some 10-15 times in Maia and to a lesser extent in Balanus, by salines containing 600 mM potassium or 2-5 mM caffeine. The increased efflux was associated with a brisk contraction.6. External application of salines containing 20, 40 or 60 mM potassium or 0.5 mM caffeine in Maia produced some stimulation of the residual efflux but no visible contraction.7. Pre-treatment of Maia fibres with 40 mM potassium or 0.5 mM caffeine salines abolished the ability of the fibres to respond to higher concentrations of these agents. A depletion of a releasable calcium fraction by these subthreshold stimuli could explain this phenomenon.8. Electrical stimulation, the injection of 50 mM calcium chloride or 50 mM caffeine produced an elevated calcium efflux which was associated with a contraction.9. Intracellular injections of EGTA only lowered the residual efflux by up to half its initial value. This suggests that calcium can be released rapidly within these muscle fibres and that the sarcoplasmic calcium concentration is not much altered from its normal value by the injection.10. The experiments suggest that in Maia, changes in the calcium efflux reflect in magnitude, but not in time course, the internal calcium changes which can be observed with the calcium-sensitive protein, aequorin.

Action Potentials↗
PubMed1970

The influx of orthophosphate into squid giant axons.

1. The influx of (32)P, applied externally as orthophosphate, into the axoplasm of squid giant axons has been studied.2. An average orthophosphate influx of 20.9 f-mole/cm(2).sec is obtained if the (32)P found in the axoplasm is assumed to be indicative of orthophosphate which has crossed the axolemma.3. The influx does not show very much dependence on external orthophosphate concentration in the range 0.02-0.5 mM.4. The influx is reduced by cyanide, 2,4-dinitrophenol, ouabain and by the absence of external potassium.5. The (32)P appears to arrive in the axoplasm as orthophosphate.6. It is concluded that there is an inward movement of orthophosphate into the axons which is mediated by an active transport process and that this may have some connexion with the active transport of sodium and potassium.

Animals↗