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Biomedical subjects

B Davis

Publications and source records attributed to B Davis.

At least 271 records · Page 15Linked to original sources
PubMed1976

Effect of acetylcholine on Cl- and Na+ fluxes across dog tracheal epithelium in vitro.

Electrical potential difference is generated across canine tracheal epithelium by active transport of Cl- toward and Na+ away from the lumen. The present study examines the effects of acetylcholine on short-circuit current, potential difference, resistance, and fluxes of 36Cl and 24Na measured across pieces of canine tracheal epithelium mounted in Ussing-type chambers. Under short-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly net ion flux toward the lumen of Cl- (n equals 7) from +1.7 +/- SE 0.5 TO +3.3 +/- SE 0.5 mueq/cm2 - h, and of Na+ (n equals 7) from -0.8 +/- SE 0.2 to +0.5 +/- SE 0.2 mueq/cm2 - h. Under open-circuit conditions, acetylcholine (5 X 10(-5) M) increased significantly the unidirectional flux of Cl- (n equals 6) toward the lumen from 4.7 +/- SE 1.3 to 5.9 +/- SE 1.4 mueq/cm2 - h, while the other measured fluxes did not change significantly, suggesting that net Cl- flux had increased toward the lumen. Atropine sulfate (10(-8) M) prevented the response to acetylcholine (5 X 10(-5) M). The increased ion flux due to acetylcholine may mediate water secretion into the airway lumen, and this secretion may have important effects on the physical properties of the liquid through which the respiratory cilia beat.

Acetylcholine↗
PubMed1976

An approach to a molecular understanding of exocytotic insulin release.

By the use of an in vitro insulin releasing system, new insights into the meechanisms underlying the insulin exocytotic process have been gained. It is proposed that insulin release is initiated by glucose interacting with a glucoreceptor on the plasma membrane. Some properties of this receptor are discussed. It is postulated that after initiation of secretion, continued insulin release is under the control of phosphorylated intermediates of glucose metabolism, i.e. glucose-6-phosphate and phosphoenol pyruvate, operating via a membrane-bound protein kinase. The initiation of insulin release by glucose, and the augmentation of this initiation by the above mentioned intermediates, is viewed as a modified cascade system. The cascade theory of insulin secretion is postulated as an alternative to the threshold distribution hypothesis of insulin secretion. The action of tolbutamide in relation to the two pool theory of insulin secretion is discussed.

Animals↗
PubMed1975

Model for extrusion of insulin beta granules.

Considerable controversy surrounds the mechanisms of insulin secretion. This hypothesis attempts to explain the events which may lead to insulin extrusion through the beta-cell membrane. The role of various effectors of insulin secretion on the activities of membrane-bound enzymes is discussed. Glucose, without effect on these enzymes, did induce insulin secretion from insulin granules and plasma membranes in vitro. The model proposes a mechanism whereby glucose may trigger first-phase insulin secretion; reinforcing mechanisms, such as raised levels of cyclic adenosine monophosphate, could augment subsequent secretion.

Adenosine Triphosphatases↗
PubMed1975

The glycolate pathway and photosynthetic competence in euglena.

The development of glycolate pathway enzymes has been determined in relation to photosynthetic competence during the regreening of Euglena cultures. Phosphoglycolate phosphatase and glycolate dehydrogenase rapidly reached maximal levels of activity but the complete development of ribulose 1,5-diphosphate carboxylase and concomitant photosynthetic carbon dioxide fixation were not attained until 72 hours of illumination. Specific inhibitors of protein synthesis showed that the formation of ribulose 1,5-diphosphate carboxylase in both division-synchronized and regreening cultures was prevented by both cycloheximide and d-threo-chloramphenicol, whereas phosphoglycolate phosphatase formation was only inhibited by d-threo-chloramphenicol but not by l-threo-chloramphenicol or cycloheximide. Since cycloheximide prevented ribulose diphosphate carboxylase synthesis and photosynthetic carbon dioxide fixation without affecting phosphoglycolate phosphatase synthesis during regreening, it was concluded that photosynthetic competence was not necessary for the development of the glycolate pathway enzymes. The inhibition of phosphoglycolate phosphatase synthesis by d-threo-chloramphenicol but not by l-threo-chloramphenicol or cycloheximide shows that the enzyme was synthesized exclusively on chloroplast ribosomes, whereas protein synthesis on both chloroplast and cytoplasmic ribosomes was required for the formation of ribulose 1,5-diphosphate carboxylase. Although light is required for the development of both Calvin cycle and glycolate pathway enzymes during regreening it is concluded that the two pathways are not coordinately regulated.

Journal Article↗
PubMed1975

Active transport of Na+ and Cl- across the canine tracheal epithelium in vitro.

The flow of water across the tracheobronchial epithelium is likely to be an important determinant of the efficiency of mucociliary clearance. Because bulk water flow has been shown to be coupled to net ion flux in several epithelia, experiments were performed to determine whether ions are transported actively by the canine tracheal epithelium. Electrical potential difference, short circuit current, and the unidirectional fluxes of positive sodium ions (Na+) and negative chloride ions (Cl-) were measured using an in vitro preparation of the posterior membranous portion of canine trachea. The values of the electrical parameters were potential difference, 30.7 +/- 2.7 mV (SE; n = 30), lumen negative to submucosa; short circuit current, 108 +/- 8 muA per cm2 (SE; n = 30). Bidirectional fluxes of Na+ and Cl- were measured both with and without continuous short circuiting of the epithelium. Under short circuit conditions there was a unidirectional flux of Cl- toward the lumen of 7.4 +/- 1.2 muEq per cm2 per hour (SE; n = 6) and toward the submucosa of 4.7 +/- 1.1 muEq per cm2 per hour (SE; n = 6), resulting in a calculated net flux of Cl- of 2.7 +/- 0.6 muEq per cm2 per hour toward the lumen. The unidirectional flux of Na+ toward the lumen was 1.3 +/- 0.5 muEq per cm2 per hour (SE; n = 8) and toward the submucosa was 2.1 +/- 0.7 muEq per cm2 per hour (SE; n = 8). This resulted in a calculated net flux of Na+ of 0.8 +/- 0.2 muEq per cm2 per hour toward the submucosa. These fluxes are consistent with active transport and together they account for the entire short circuit current. Under open circuit conditions, the calculated net fluxes of Cl- and Na+ were not significantly different from zero.

Animals↗
PubMed1974

The Effect of Light on the Synthesis of Mitochondrial Enzymes in Division-synchronized Euglena Cultures.

The development of the mitochondrial enzymes fumarase and succinate dehydrogenase has been followed in Euglena cultures division-synchronized by 14-hour light periods alternating with 12-hour dark periods. The activity of both enzymes was unaltered over the light phase, doubled in early dark phase, and thereafter remained constant over the rest of the cycle. The increase in enzyme activity in early dark phase probably represented de novo enzyme synthesis because it was prevented by the addition of cycloheximide at a concentration known to inhibit protein synthesis on Euglena cytoplasmic ribosomes.When division-synchronized cultures were darkened in early light phase, a doubling of both fumarase and succinate dehydrogenase activity resulted, showing that light was repressing enzyme synthesis. The addition of acetate did not have a similar effect to darkening cultures: enzyme activity being unaltered over the light phase of the cycle. Enzyme expression was also unaffected by the addition of 3-(3,4 dichlorophenyl)-1,1-dimethylurea, a potent inhibitor of photosynthetic carbon dioxide fixation. The addition of 6-methylpurine (an inhibitor of transcription) at the beginning of the light phase inhibited enzyme increase in early dark phase, but when added at a later stage of the light phase (hour 8), increase in enzyme activity in early dark phase was unaffected. We concluded that transcription for these enzymes occurs in early light phase but light exerts a post-transcriptional control so that enzyme synthesis does not result until cells enter the dark phase of the cell cycle.

Journal Article↗