PubMed Health⌕ Search

Biomedical subjects

D R Saunders

Publications and source records attributed to D R Saunders.

5 recordsLinked to original sources
PubMed1979

Light dependence of the decay of the proton gradient in broken chloroplasts.

The initial rates and steady-state values of proton uptake by broken chloroplasts have been measured as functions of light intensity at various concentrations of chlorophyll, pyocyanine, supporting electrolyte, buffer, as well as pH and temperature. Kinetics analysis of the data shows that the rate of decay of proton gradient due to backward leakage depends on light intensity. Under steady illumination, the decay constant kL is equal to kD + mR0, where R0 is the initial rate of proton uptake which is a function of light intensity, kD is the decay constant in the dark and m is a parameter which is independent of light intensity. Treatment of chloroplasts with lysolecithin, neutral detergent, 2,4-dinitrophenol, or valinomycin in the presence of K+ increases kD without affecting m. Treatment with N,N'-dicyclohexylcarbodiimide or adenylyl imidodiphosphate under appropriate conditions decreases m without affectsity and hence m = 0. These results suggest that the light-dependent part (mR0) of kL is due to leakage of protons through the coupling factor (CF1-CF0) complex which can open or close depending on light intensity and that the light independent part (kD) of the decay constant kL is due to proton leakage elsewhere.

Adenylyl Imidodiphosphate↗
PubMed1979

Effect of calcium on absorption of fatty acid by rat jejunum in vitro.

The effect of Ca++ on jejunal osmiophilic particles was studied in a recirculating system which was not contaminated with plasma lipoproteins. An isolated, infused segment of rat jejunum was suspended in a bath of liquid paraffin. Transudate, containing osmiophilic particles, appeared like beads of sweat on the serosal surface, and fell to the bottom of the bath. In the range of 25-38 C, 30 C proved to be optimal for histological preservation of villous architecture. Production of transudate, 20 mg/min/g of jejunum, and transport of [14C] oleate proceeded nearly linearly after the first 30 min. Necrosis of mid-villus and crypt cells became obvious by light microscopy after one hour. Therefore, transudate was collected between the period of 30-60 min. Shadow casting of transudates, produced when saline was infused, revealed that 86 +/- 9 (SD) % of osmiophilic particles was less than 800 A in diameter; 13 +/- 8% was 800-1000 A; 0.4 +1- 0.5% was 1000 - 2000 A. Corresponding values were 58 +/- 10, 25 +/- 5, and 16 +/- 5% when 5 mM [14C] oleate + 2.5 mM monoolein was infused; 75% of the transported [14C] appeared in triglyceride. Adding 2 mM Ca++ to the infusion doubled the transport of [14C] triglyceride without increasing particle size further. We conclude that luminal Ca++ increases the absorption of luminal fatty acid by rat jejunum in vitro.

Albumins↗
PubMed1978

Effect of phenolphthalein on the function and structure of rodent and human intestine.

Phenolphthalein (PHE) is the active ingredient in at least 12 over-the-counter laxative preparations. It is alleged to have a minor effect in the small intestine compared with the colon where it is supposed to alter motor activity or water absorption or both. We measured water absorption from segments of rat intestine in vivo, and from the nearly intact small intestines of patients with established ileostomies. In rats, each intestinal segment served as its own control so that water absorption in a test period (PHE, 1--15 mg/100 ml) could be expressed as a percentage of the control period when buffer was infused. PHE inhibited water absorption, and the degree of inhibition was related linearly to log10 PHE concentration. The similarity of slopes of the regression lines suggested that all segments of the rat intestine were equally sensitive to PHE. In six patients, PHE, 100 mg four times a day, increased weight of ileostomy output by 30%, and Na+ output by 39%. These facts indicate that some of the laxative effects of PHE result from inhibition of water absorption in both large and small intestines.

Animals↗
PubMed1978

Apoprotein synthesis by human duodenojejunal mucosa.

We tested whether human duodenojejunal mucosa is able to synthesize apoproteins from amino acid precursors because lipoprotein-like particles are visualized by electron microscopy in human absorptive cells and because apoproteins are synthesized by the perfused rat intestine. Duodenojejunal biopsies from 21 normal fasting volunteers were incubated with L-[U-14C]leucine; 15.6 +/- 3.3 nmoles of the [14C]leucine was incorporated into protein by 100 mg wet weight of biopsies during an incubation of 2 hr. No [14C]leucine was incorporated by boiled biopsies. Homogenates of incubated biopsies were fractionated by ultracentrifugation: 43 +/- 2% of the incorporated 14C as found in the d less than 1.006 fraction; 3.2 +/- 0.6%, 8.1 +/- 1.0% and 48 +/- 2% were found to be associated with the d = 1.006 to 1.063, d = 1.063 to 1.25, and d greater than 1.25 fractions, respectively. The specific activity in the d less than 1.006 fraction was 5.6 times greater than that in the other fractions. Of the 14C incorporated into the d less than 1.006 fraction, 10.8, 7.2, and 7.1% were specifically precipitated by rabbit antihuman apoproteins A-I, A-II, and B, respectively. Of the 14C incorporated into the d = 1.006 to 1.063 fraction, 11.3 4.1, and 8.5% were specifically precipitated by rabbit antihuman apoprotein A-I, A-II, and B, respectively. Approximately 5% of the 14C incorporated by the d = 1.063 to 1.25 fractions were precipitated by rabbit antihuman apoprotein A-I or A-II. None of the d less than 1.25 fractions precipitated a significant amount of radioactivity with rabit antihuman apoprotein C-II, or antiarginine-rich apoprotein. None of the antibodies precipitated radioactivity from the d greater than 1.25 fraction. These experiments suggest that human duodenojejunal mucosa is able to synthesize in vitro apoproteins A-I, A-II, and B from amino acid precursors. The specificity of the immunoprecipitates was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis.

Adolescent↗