Modeling Biological Membranes with Circuit Boards and Measuring Electrical Signals in Axons: Student Laboratory Exercises

This is a demonstration of how electrical models can be used to characterize biological membranes. This exercise also introduces biophysical terminology used in electrophysiology. The same equipment is used in the membrane model as on live preparations. Some properties of an isolated nerve cord are investigated: nerve action potentials, recruitment of neurons, and responsiveness of the nerve cord to environmental factors.     

A further geranylnerol derivative from Helianthopsis species

The investigation of three species of the new genus Helianthopsis gave in all cases furoheliangolides, as well as kaurenic, tricholobanic and beyerenic acids. Furthermore, a new geranylnerol derivative was isolated from H. bishopii. The chemotaxonomy is discussed briefly.     

SYMMETRY VERSUS ASYMMETRY IN SEXUAL ISOLATION EXPERIMENTS

Two hypotheses predicting the ancestral or derived status of populations and based on asymmetrical mate discrimination (Kaneshiro, 1976; Watanabe and Kawanishi, 1979) were tested using nine laboratory populations of D. simulans, a highly outcrossed ancestral population, and eight populations derived from it via founder-flush-crash cycles. The data from individual mating tests using pairwise combinations of these populations fit the Kaneshiro hypothesis reasonably well, rejecting the Watanabe-Kawanishi hypothesis. However, more powerful tests rejected the Kaneshiro hypothesis for the data we analyzed. The values for derived females predicted by the Kaneshiro hypothesis were biased: they were consistently high for derived males and consistently low for ancestral males. We propose a hypothesis, based on variation in mating propensities and symmetrical mate discrimination. We assessed the power of Kaneshiro's and our hypotheses to predict the number of matings between derived females and derived males by plotting predicted vs. observed values and fitting these points to the expected line of unit slope passing through the origin. Predictions of our hypothesis explained more of the variance (r² = 0.87) than predictions of the Kaneshiro model (r² = 0.63). While asymmetrical sexual isolation undoubtedly occurs between some species, its existence cannot be determined simply by measuring mating frequencies in a single experiment.     

Chromenes from ageratina riparia

The reinvestigation of the roots and aerial parts of Ageratina riparia afforded ten new chromenes, their structures being determined by spectral data and chemical transfomrations.     

Balancer Fine Structure of the Pleurodeles Larva

The paired balancers of larval Pleurodeles waltl, a urodelan species of the Amphibia, were investigated throughout their life span until final degeneration, using electron microscopy. The evidence from cellular ultrastructure illustrates the mucus-secreting function of these organs, and the outer epithelial cells actively synthesize muco-proteinaceous substance. An extensive granular endoplasmic reticulum and well developed Golgi complexes participate in the mucus manufacture. The balancer epidermis is also extensively innervated throughout by non-myelinated neurites, most of them without Schwann cells, a feature which argues strongly in favour of the organ also having a sensory function, whose nature has yet to be determined.     

Development of Antipredator Responses in Snakes

Individual and litter differences in the number of attacks directed by Mexican garter snakes (Thamnophis melanogaster) at a threatening stimulus were studied over the first year of life. Newborn snakes born to wildcaught females from the same population were tested the day after they were born and at 7, 16, 31, and 54 weeks of age on reactivity to a potent nonmoving and moving stimulus (a human finger). There were significant individual and interlitter differences in number of strikes directed at both stimuli but no significant effect of sex. Intercorrelations among the strike scores of individuals across test days averaged .54 for the nonmoving stimulus presentations and .63 for trials with the moving stimulus. Strike scores to the moving and nonmoving stimuli were significantly correlated at each age, however, attack responses to the moving stimulus declined over the year while those to the nonmoving stimulus remained constant. Measures of concordance showed that both individual strike scores and litter means were highly consistent, whereas consistency within litters was reduced. The results indicate that litter and individual differences among newborn snakes in the tendency to engage in antipredator behavior (“defensive temperament”) remain relatively stable from the first day after birth throughout the first year of life.     

Influence of thyroid hormone status on expression of genes encoding G protein subunits in the rat heart.

We have studied the influence of thyroid hormone status in vivo on expression of the genes encoding guanine nucleotide-binding regulatory protein (G protein) alpha-subunits Gs alpha, Gi alpha(2), Gi alpha(3), and both the 36-kDa form (beta 1) and the 35-kDa form (beta 2) of the beta-subunit in rat ventricle. The relative amounts of immunoactive Gi alpha(2) and Gi alpha(3) were greater in ventricular membranes from hypothyroid animals than from euthyroid animals (1.9- and 2.6-fold, respectively). A corresponding 2.3-fold increase in Gi alpha(2) mRNA was observed as well as a 1.5-fold increase in Gi alpha(3) mRNA. The relative amounts of immunoactive beta 1 and beta 2 polypeptides were also increased (2.8- and 1.8-fold, respectively) in the hypothyroid state and corresponded with comparable increases in the relative levels of beta 1 and beta 2 mRNAs. No difference was seen between the amounts of Gi alpha(2), Gi alpha(3), beta 1, and beta 2 in the euthyroid state and the hyperthyroid state. In contrast to these effects of thyroid hormone status on Gi alpha and beta, the steady-state amounts of Gs alpha protein and mRNA were not altered by thyroid hormone status. Thyroid hormone status did not alter sensitivity of adenylyl cyclase to stimulation by sodium fluoride or guanyl-5'-yl imidodiphosphate (GppNHp), nor did it influence GppNHp-induced inhibition of forskolin-stimulated enzyme activity. These results demonstrate that thyroid hormone status in vivo can regulate expression of specific G protein subunits in rat myocardium. However, the physiological consequences of these changes remain unclear.     

Essential trace metals and specific organ weights in diet-restricted and ad lib-fed rats

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 μm). The average exposure concentration was controlled from low level (0.6 mg/m³) to high level (8.0 mg/m³) and total exposure time ranged from 140 to 216 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for a 1-yr clearance period before sacrifice. There were no differences in body weight gain between NiO exposure groups and controls. Nickel concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of nickel was observed in liver, kidney, spleen, heart, brain, and blood, but lung burdens of up to about 2.35 mg of NiO were found. The apparent deposition fractions were 19.8 and 14.5% after the exposure to average concentrations of 1.4 and 6.5–7.0 mg/m³, respectively. The clearance rate of NiO deposited in lungs may be small.     

Investigation of differences in the tertiary structures of food proteins by small-angle X-ray scattering

Summary With current emphasis in bioengineering on developing new and better structure-function relationships for proteins (e.g., the need for predictability of expected properties prior to cloning), practical and reliable methodology for providing characterization of appropriate features has become of increasing importance. The most potent and detailed technique, X-ray crystallography, has severe limitations: it is so demanding and time-consuming that X-ray coordinates are frequently unavailable for materials of interest; its data relate to static and essentially unhydrated structures, whereas proteins exhibit a variety of dynamic features and function in an aqueous environment; and many proteins of technological importance may never be crystallized. Small-angle X-ray scattering, however, is particularly suitable as a methodology that can provide a substantial number of significant geometric parameters consistent with crystallographic results, that can readily show tertiary structural changes occurring under varying conditions, and that can deal with solutions and gels. Results are presented here from small-angle X-ray scattering investigations of the apo and holo forms of chicken egg-white riboflavin-binding protein, chicken egg-white lysozyme, bovine milk-whey -lactalbumin and -lactoglobulin, and bovine ribonuclease. We utilize these observations to compare tertiary structures of these proteins as well as conformational changes in these structures, and to provide a basis for discussion of their physical and biological significance.Agricultural Research Service, U.S. Department of Agriculture. Reference to brand or firm name does not constitute endorsement by the U.S. Department of Agriculture over others of a similar nature not mentioned.