Degradation of the 32 kD Herbicide Binding Protein in Far Red Light

White light (400-700 nanometers) supports the activity of photosystem I (PSI) and photosystem II while far red light (≥700 nanometers) supports PSI almost exclusively. In intact fronds of Spirodela oligorrhiza, turnover of the 32 kilodaltons herbicide binding protein is stimulated under both these light conditions, although not in the dark or at wavelengths >730 nanometers. As is the case in white light, the far red light induced degradation of the protein is inhibited by DCMU. The means by which far red light operates is unclear. Hypotheses considered include: PSI activated proteolysis, PSI-induced formation of semiquinone anions, and PSI-generated free radicals.     

Temperature-sensitive steps in the secretory pathway for von Willebrand factor in endothelial cells

The effect of reduced temperature on the post-translational processing and stimulated release of von Willebrand factor (vWf) from human umbilical vein endothelial cells was studied. Following pulse-labeling, cells were incubated for 4 h at 18 degrees C or 20 degrees C. Post-translational processing was reversibly arrested at the dimer stage, dimers were composed of Endo H-sensitive precursor subunits, and no vWf was detected in the culture medium. This block was reversible, since warming cells to 37 degrees C relieved it and resulted in the appearance of fully processed vWf in the cells and the culture medium. The same results were obtained when cells were incubated with carbonyl cyanide m-chlorophenol hydrazone or dinitrophenol which inhibit mitochondrial oxidative phosphorylation, known to block exit of secretory proteins from the endoplasmic reticulum (ER). This indicated that ER exit is not required for the complete dimerization of vWf. Reduced temperature (18 degrees C and 20 degrees C) also reversibly and nearly completely inhibited the secretagogue-induced release of vWf from Weibel-Palade bodies without affecting the microtubular cytoskeleton. We add reduced temperature to the list of useful tools for the study of the vWf secretory pathway in endothelial cells.     

Panting and acid-base regulation in heat stressed birds

1. Studies in respiratory physiology and acid-base balance of panting birds exposed to high Tas show that flying as well as nonflying birds can use the respiratory system simultaneously for gas exchange and evaporative cooling. 2. The present study proves that well acclimated hand-reared birds can effectively regulate a normal CO2 level and acid-base status in arterial blood, when exposed to extremely high temperatures (50-60 degrees C). 3. In many birds practising simple or "flush-out" panting, the dead space can be reduced to a volume which is estimated to be approx 15% the volume of the respiratory tract. 4. These two modes of ventilation, shallow and high-rate, restricted to the nonrespiratory surfaces, may ensure the avoidance of CO2-washout and limit lung ventilation to the volumes needed for oxygen consumption. 5. This view supports earlier theories, suggesting the existence of physiological shunt mechanisms which operate during thermal panting in birds.     

The effect of heat exposure on blood chemistry of the hyperthermic rabbit

1. Two hours of exposure to heat stress, resulted in hyperthermia in rabbits (Oryctolagus cuniculus). 2. This was accompanied by a severe hypocapnia, partly compensated for by a significant decrease in bicarbonate (HCO3-) concentration. 3. The severest hyperthermia (Tb = 43.5 degrees) was followed by a sharp decreased in both PaCO2 (to 20.2 torr) and HCO3- (to 9.2 mM/l), resulting in extreme metabolic acidosis (pH = 7.290). 4. The significant increase in serum osmolality (27%) is interpreted by the cumulative effect of increased electrolyte and metabolite concentrations. 5. The elevation in blood BUN, creatinine, globulin and GOT levels point to a possible damage to muscle cells by hypothermia. 6. The stable cholesterol and alkaline phosphatase levels, suggest that liver tissue was not damaged. 7. The dramatic increase in glucose from 103.8 to 348.8 mg%, and the significant increase (from 22.0 to 39.9 mg%) in BUN, suggest a possible disability of the cells to metabolize carbohydrates, accompanied by a progressive proteolysis as an alternative process for energy production. 8. The data suggest that the emergence of muscle cell damage, severe hyperglycemia and acidosis under heat stress, precedes and amplifies the deteriorating effects of high Tb in heat stressed rabbits, which often lead to mortality.     

Multiple modes of a conditional neural oscillator

We present a model for a conditional bursting neuron consisting of five conductances: Hodgkin-Huxley type time- and voltage-dependent Na⁺ and K⁺ conductances, a calcium activated voltage-dependent K⁺ conductance, a calcium-inhibited time- and voltage-dependent Ca⁺⁺ conductance, and a leakage Cl(_– conductance. With an initial set of parameters (versionS), the model shows a hyperpolarized steady-state membrane potential at which the neuron is silent. Increasingg _Na and decreasingg _Cl, whereg _i , is the maximal conductance for speciesi, produces bursts of action potentials (BursterN). Alternatively, an increase ing _Ca produces a different bursting state (BursterC). The two bursting states differ in the periods and amplitudes of their bursting pacemaker potentials. They show different steady-stateI–V curves under simulated voltage-clamp conditions; in simulations that mimic a steady-stateI–V curve taken under experimental conditions only BursterN shows a negative slope resistance region. ModelC continues to burst in the presence of TTX, while bursting in ModelN is suppressed in TTX. Hybrid models show a smooth transition between the two states.     

Substance P-like immunoreactivity in the stomatogastric nervous systems of the crab Cancer borealis and the lobsters Panulirus interruptus and Homarus americanus

Summary The distribution of substance P-like immunoreactivity in the stomatogastric nervous systems of three decapod crustacean species, Cancer borealis, Homarus americanus, and Panulirus interruptus, was studied. The stomatogastric ganglion showed dense staining in the neuropil, but none in the somata. A single neuron stained in the esophageal ganglion. Lucifer yellow backfills and intracellular injections followed by incubation with the substance P antibody showed that the axons of this neuron project into the inferior esophageal nerves towards the paired commissural ganglia. The commissural ganglia showed a pronounced projection from a large bundle of fibers in the anterior medial portion of the circumesophageal connective. Additionally, less dense neuropil and stained somata were seen in the commissural ganglia. Staining was completely blocked by preabsorption with authentic substance P, physalaemin, eledoisin, and substance K. These data suggest that in the nervous system of crustacean species a molecule with C-terminal homology to substance P and other tachykinins is released as a neuroregulator in the stomatogastric ganglion.     

Comparison of structures of various human fibrinogens and a derivative thereof by a study of the kinetics of release of fibrinopeptides

The kinetics of the thrombin-induced release of fibrinopeptides from several variants of human fibrinogen, and from the plasmin digestion fragment E thereof, have been studied by using an HPLC technique to separate the reaction products. The data were analyzed in terms of a Michaelis-Menten mechanism in which the A alpha and B beta chains compete for thrombin. Phosphorylation of Ser-3 of the A alpha chain appears to increase the rate of release of the corresponding phosphorylated peptide A from fibrinogen, due to enhanced binding of thrombin (lower value of the Michaelis-Menten constant KM). However, phosphorylation does not affect the rate of release of the unphosphorylated A or B peptides. Increase in the length of the gamma chain (at the C-terminus) does not affect the rate of release of any of the fibrinopeptides. The rate of release of the A peptide from fragment E (which is devoid of the B peptide) is similar to that for the complete fibrinogen molecule. These results are in agreement with an earlier conclusion [Martinelli, R. A., & Scheraga, H. A. (1980) Biochemistry 19, 2343] that the A alpha and B beta chains behave independently in their competition for thrombin; i.e., the hydrolyzable Arg-Gly bonds of the A alpha and B beta chains are both accessible to thrombin.     

d-Amphetamine raises serum prolactin in man: evaluations after chronic placebo, lithium and pimozide treatment.

One of the major biochemical effects of d-amphetamine is the release and uptake inhibition of dopamine (DA). We measured the effect of d-amphetamine upon prolactin release which is inhibited by DA and stimulated by serotonin. d-Amphetamine (20 mg i.v.) significantly raised the serum prolactin levels of drug-free schizophrenic patients over preinfusion levels and levels following a paired placebo lactose infusion. Amphetamine infusions were repeated after both chronic DA blockade with pimozide and after chronic lithium treatment that has been reported to attenuate amphetamine effects. These chronic pretreatments did not prevent significant increases in prolactin following d-amphetamine infusions. Pimozide raised preinfusion prolactin levels but lithium had no effect. Further studies are needed to clarify the d-amphetamine-induced rise in prolactin.