Influence of ventrolateral surface of medulla on reflex tracheal constriction

To assess the role of structures located superficially near the ventrolateral surface of the medulla on the reflex constriction of tracheal smooth muscle that occurs when airway and pulmonary receptors are stimulated mechanically or chemically, experiments were conducted in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated cats. Pressure changes within a bypassed segment of the trachea were used as an index of alterations smooth muscle tone. The effects of focal cooling of the intermediate areas or topically applied lidocaine on the ventral surface of the medulla on the response of the trachea to mechanical and chemical stimulation of airway receptors were examined. Atropine abolished tracheal constriction induced by mechanical stimulation of the carina or aerosolized histamine, showing that the responses were mediated over vagal pathways. Moderate cooling of the intermediate area (20 degrees C) or local application of lidocaine significantly decreased the tracheal constrictive response to mechanical activation of airway receptors. Furthermore, when the trachea was constricted by histamine, cooling of the intermediate area significantly diminished the increased tracheal tone, whereas rewarming restored tracheal tone to the previous level. These findings suggest that under the conditions of the experiments the ventral surface of the medulla plays an important role in constriction of the trachea by inputs from intrapulmonary receptors and in the modulation of parasympathetic outflow to airway smooth muscle.     

Cooperative binding of oxygen to hemoglobin: analysis of accurate equilibrium binding data

Accurate equilibrium binding data for the oxygenation of hemoglobin are used (a) to show that various models for cooperativity are inconsistent with the best available experimental data, (b) to determine the equilibrium constants for binding of 2,3-diphosphoglycerate to hemoglobin molecules in intermediate stages of oxygenation, and (c) to deduce a mechanism for allosteric effects in hemoglobin which is consistent with the best available experimental data. The total free energy of cooperativity is defined and discussed.     

DETERMINATION OF GUSTATORY SUCROSE THRESHOLD IN WATER BY USE OF A LINEAR SUCROSE GRADIENT

A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)).     

High concentration active enzyme centrifugation studies with pig kidney phosphofructokinase. Detection of 9.8 S, 25 S, and 53 S active polymeric forms

This laboratory has carried out the first detailed studies of the active polymeric forms of phosphofructokinases over the concentration region of 1 to 1200 micrograms/ml. This includes the concentration range in which the enzymes exist in vivo and the concentration range in which their association-dissociation equilibria shift to yield various polymeric forms. Previously, active enzyme centrifugation experiments were limited to the concentration range below a few micrograms per ml. The present experiments were made possible by the recent development in this laboratory of a new technique called high concentration active enzyme centrifugation (Wei, G. J., and Deal, W. C., Jr. (1979) Biochemistry 18, 1129). We report here three new active polymeric forms of pig kidney phosphofructokinase which have been observed in high concentration active enzyme centrifugation experiments. These include: 1) a 9.8 S form (Mr = 2.6 X 10(5)); 2) a 25 S form (Mr = 1.01 X 10(6)); and 3) a 53 S form (too asymmetric to estimate Mr). In addition, a 5.4 S form is predicted from the Mr (8.8 X 10(4)) of the polypeptide chain obtained from sodium dodecyl sulfate gel electrophoresis; it is not known whether or not it is active. The 9.8 S value is the limiting sedimentation coefficient value observed in active enzyme centrifugation experiments. The 25 S form is indicated by a plateau in the 50 to 200 micrograms/ml region of the s versus c curve. The 53 S form is observed as a plateau in the 600 to 1000 micrograms/ml region of the s versus c curve.     

In vivo intermembrane transfer of phospholipids in the photosynthetic bacterium Rhodopseudomonas sphaeroides.

The kinetics of accumulation of phospholipids into the intracytoplasmic membrane of Rhodopseudomonas sphaeroides have been examined. We have previously demonstrated that accumulation of phospholipids in the intracytoplasmic membrane is discontinuous with respect to the cell cycle. In this study we demonstrated a sevenfold increase in the rate of phospholipid incorporation into the intracytoplasmic membrane concurrent with the onset of cell division. Pulse-chase labeling studies revealed that the increase in the rate of phospholipid accumulation into the intracytoplasmic membrane results from the transfer of phospholipid from a site other than the intracytoplasmic membrane, and that the transfer of phospholipid, rather than synthesis of phospholipid, is most likely subject to cell cycle-specific regulation. The rates of synthesis of the individual phospholipid species (phosphatidylethanolamine, phosphatidyglycerol, and an unknown phospholipid) remained constant with respect to one another throughout the cell cycle. Similarly, each of these phospholipid species appeared to be transferred simultaneously to the intracytoplasmic membrane. We also present preliminary kinetic evidence which suggested that phosphatidylethanolamine may be converted to phosphatidycholine within the intracytoplasmic membrane.