Brain hypoxia and control of breathing: neuromechanical control

The effects of graded brain hypoxia on respiratory cycle timing, the lung inflation reflex, and respiratory compensation for an inspiratory flow-resistive load were studied in unanesthetized goats. Two models, inhalation and CO and acute reduction of brain blood flow (BBF) were used to produce comparable levels of brain hypoxia. The lung inflation reflex was assessed as the ratio of inspiratory time of an occluded breath to that of the preceding spontaneous breath (TIoccl/TIspont). Compensation for flow-resistive loading was assessed as the effect of the load upon the airway occlusion pressure response to rebreathing CO2 (delta P 0.1/delta PCO2). Major findings were 1) severe brain hypoxia (HbCO of 60% or BBF of 42%) caused tachypnea due to a 50% or more reduction of expiratory time but only a 20% or less reduction of inspiratory time; 2) moderate carboxyhemoglobinemia (HbCO of 25-30%) enhanced TIoccl/TIspont from 1.5 +/- 0.1 at control to 2.1 +/- 0.1, while severe brain hypoxia (HbCO of 60% and BBF of 42%) reduced the ratio to 1.0 +/- 0.2; and 3) compensation for a flow-resistive load, manifested by increases of delta P 0.1/delta PCO2 of 75-300% in the control state, was abolished at HbCO of 45-50% and BBF of 60%. The data suggest that in unanesthetized animals brain hypoxia elicits tachypnea largely by an effect on the expiratory phase of the bulbopontine timing mechanism. The observed enhancement of the lung inflation reflex and abolition of flow-resistive load compensation are best explained by hypoxic depression of higher than brain stem neural function.     

Protein-lipid interaction. Biophysical studies of (Ca2+ + Mg2+)-ATPase reconstituted systems

Differential scanning calorimetry, fluorescence spectroscopy and freeze-fracture electron microscopy have been applied to a study of the reconstituted Ca2+-ATPase proteins from sarcoplasmic reticulum when they are incorporated into pure lipid/water systems. The results obtained with these techniques have been used to examine the effects of this intrinsic protein upon the surrounding lipid at temperatures above and below the main lipid solid-fluid phase transition temperature (Tc). 1. Above this Tc value, the freeze-fracture data show that the proteins are randomly distributed within the plane of the bilayer. The fluorescence data show that as the protein content in the bilayer increases, so does the 'microviscosity'. 2. Below Tc the proteins occur in high protein to lipid patches, separate from the remaining crystalline lipid. The fluorescence data indicate that at these temperatures the presence of the protein causes a decrease in microviscosity, whilst the calorimetric data indicate a decrease in enthalpy of the main lipid transition. 3. A premelting of the high protein to lipid patches formed by phase separation within the lipid bilayers is indicated by the calorimetric and fluorescence data. This observation is used to rationalise the 'anomalous' properties of the dipalmitoyl phosphatidylcholine-ATPase of exhibiting activity at temperatures well below the lipid phase transition at 41 degrees C.     

Effect of calcium on differentiation of Friend leukemia cells

Induction of hemoglobin synthesis of Friend leukemia cells is inhibited by changing the ratio between internal and external Ca²⁺ concentrations. The concentration ratio can be successfully manipulated by the addition of the growth medium of (1) Ca²⁺ channel blocker D600 (90 nM-4 × 10² nM), (2) Ca²⁺ ionophore A23187 (1 × 10²–2 × 10² nM), and (3) EGTA at molar concentrations comparable to the Ca²⁺ concentration of the medium formulation (3 × 10² μM). The observations suggest that a specific ratio between intra- and extracellular Ca²⁺ is required for erythroid differentiation to proceed.     

Fasciola hepatica: A proteolytic digestive enzyme

A proteolytic enzyme in the gut exudate of the common liver fluke has been purified. The enzyme is specific for globin with a pH optimum of 3.9–4.0 and breaks the protein down to peptides and a small percentage of free amino acids. Collagenase activity at pH 7.5 copurifies with the main globinolytic enzyme. The enzyme has a molecular weight of 12,000 and does not appear to be antigenic in fluke-infected animals.     

Bacteriorhodopsin,boundary lipid and protein conformers. A spin label study

A spin label study, as a function of temperature, has been made with the bacteriorhodopsin membrane using a stearic acid spin label. The ESR spectra show a strong variation with temperature and the presence of isosbestic points. The spectra are interpreted as indicating the presence of a two-component system with an activation energy (approx. 14 kcal/mol) corresponding to a protein conformational change. This activation energy is similar to that deduced from recent flash photolysis studies.It is concluded that the spin label is sensitive to the temperature-dependent protein conformational change in this membrane system.     

Infanticide and fertility among Eskimos: A computer simulation

Until recently, certain Eskimo groups were reported to practice female infanticide in the belief that the time spent suckling a girl would delay the mother's next opportunity to bear a son, males being preferred to females because of their future role as providers in a hunting economy. From sex ratios in census data, rates of female infanticide of up to 66% for some groups have been inferred, leading some ethnographers to conclude that these groups were headed for extinction. Eskimo beliefs regarding the effects of infanticide on fertility, however, are in accord with the results of research on the relation of fertility and lactation: The cessation of lactation following infanticide would significantly shortern the expected interval until the next birth. Given this fact and available field data regarding the parameters of Eskimo population growth, the present computer simulation indicates that Eskimo populations could sustain a rate of 30% female infanticide and still survive. Higher reported rates are explained as the combined result of female infanticide plus the tendency of ethnographers to overestimate to overestimate the ages of juvenile females relative to juvenile males.     

The staining pattern of collagen fibrils. Improved correlation with sequence data.

The periodic banding pattern of stained collagen fibrils observed in the electron microscopic can be correlated with the charge distribution deduced from the amino acid sequence. Earlier work used alpha 1 chain sequence data only. The present study incorporates alpha 2 as well as alpha 1 sequence data, so that the complete distribution of charged residues is used. Correlation is improved if it is supposed that the extrahelical terminal regions are contracted. The optimal value of the periodicity, D, (previously 232.3 +/- 0.5 residues using alpha 1 data only), is now 234.2 +/- 0.5 residues, assuming uniform spacing of residues in the helical body of the molecule. This value agrees better with values obtained by others from analyses of interactions between molecules, using sequence data alone. Using the improved value of D, the relative axial locations of the charged residues in the fibril are displayed. In this way, the charged residues contributing to each band in the fibril staining pattern can be identified.     

Seasonal Changes in the Structure and Function of Mitochondrial Membranes of Artichoke Tubers: A Requisite for Surviving Low Temperatures during Dormancy

The temperature limits of the order-disorder transition, and the Arrhenius activation energy of succinate oxidase activity for mitochondria of Jerusalem artichoke (Helianthus tuberosus L.) tubers were determined from the initiation to the termination of dormancy. The temperature limits for the transition at the initiation of dormancy were 25 and 3 C. These changed to 9 and −5 C at mid-dormancy and returned to 25 and 2 C at the termination of dormancy. The Arrhenius activation energy measured in the temperature range above the transition was 35 kilojoules per mole at middormancy and decreased to 17 kilojoules per mole at the termination of dormancy when sprouting was evident. The coincidence of the changes in membrane structure and function with dormancy suggests that artichokes possess a mechanism for regulating membrane lipid structure so that cellular integrity of tuber tissue is maintained even when the tubers are exposed to low temperatures.     

The control of food mobilisation in seeds of Cucumis sativus L.

The development of maximal rates of lipid and protein hydrolysis in cucumber cotyledons depends upon the removal of the testa and the presence of the embryonic axis. The testa appears to exert at least part of its inhibitory influence by suppressing the development of enzyme activity associated with lipolysis and proteolysis. There is, however, no evidence to suggest that the presence of the embryonic axis is a pre-requisite for the development of optimal enzyme activity.Abbreviations TLC thin layer chromatography - GC-MS gas chromatography-mass spectrometry - GLC gas-liquid chromatography - TCA trichloroacetic acid