Rat pregnancy and parturition survive spaceflight challenge: new considerations of developmental consequences

Results of the NASA-NIH.R1 and NASA-NIH.R2 pregnant rat studies are reported and compared with results of Cosmos-1514 study. Similarities and differences between the Cosmos and STS flights are reviewed. STS rats were videotaped so that in-flight and post-flight behavior could be observed. Rats were observed during readaptation to 1-g and labor and delivery. Results indicate that pregnancy can proceed after exposure to microgravity and that vaginal delivery can occur despite readaptation to 1-g. Analysis of videotape revealed that flight dams experienced almost twice as many labor contractions as controls.     

Estimation of pentobarbital hydroxylase activity by gas-liquid chromatography

A method is presented for the estimation by gas-liquid chromatography of the in vitro metabolism of pentobarbital to its alcoholic metabolite, hydroxypentobarbital (5-ethyl-5-(1′-methyl-3′-hydroxybutyl) barbituric acid). The parent compound and metabolite are extracted from the incubation medium with ethyl acetate, the ethyl acetate is removed, and the trimethylsilyl derivatives are formed. These are separated and the metabolite quantitated on a gas-liquid chromatograph with a hydrogen flame ionization detector. As little as 1% metabolism can be readily determined. The identification of the products was confirmed by thin-layer chromatography and combination gas-liquid chromatography-mass spectrography. The present method offers a compromise between the sensitivity of the method employing radiolabeled pentobarbital and the convenience of measuring the disappearance of substrate.     

The conduction of protons in different stereoisomers of dioxolane-linked gramicidin A channels

Two different stereoisomers of the dioxolane-linked gramicidin A (gA) channels were individually synthesized (the SS and RR dimers;. Science. 244:813-817). The structural differences between these dimers arise from different chiralities within the dioxolane linker. The SS dimer mimics the helicity and the inter- and intramolecular hydrogen bonding of the monomer-monomer association of gA's. In contrast, there is a significant disruption of the helicity and hydrogen bonding pattern of the ion channel in the RR dimer. Single ion channels formed by the SS and RR dimers in planar lipid bilayers have different proton transport properties. The lipid environment in which the different dimers are reconstituted also has significant effects on single-channel proton conductance (g(H)). g(H) in the SS dimer is about 2-4 times as large as in the RR. In phospholipid bilayers with 1 M [H(+)](bulk), the current-voltage (I-V) relationship of the SS dimer is sublinear. Under identical experimental conditions, the I-V plot of the RR dimer is supralinear (S-shaped). In glycerylmonooleate bilayers with 1 M [H(+)](bulk), both the SS and RR dimers have a supralinear I-V plot. Consistent with results previously published (. Biophys. J. 73:2489-2502), the SS dimer is stable in lipid bilayers and has fast closures. In contrast, the open state of the RR channel has closed states that can last a few seconds, and the channel eventually inactivates into a closed state in either phospholipid or glycerylmonooleate bilayers. It is concluded that the water dynamics inside the pore as related to proton wire transfer is significantly different in the RR and SS dimers. Different physical mechanisms that could account for this hypothesis are discussed. The gating of the synthetic gA dimers seems to depend on the conformation of the dioxolane link between gA's. The experimental results provide an important framework for a detailed investigation at the atomic level of proton conduction in different and relatively simple ion channel structures.     

Allosteric activation mechanism of the alpha1beta2gamma2 gamma-aminobutyric acid type A receptor revealed by mutation of the conserved M2 leucine

A conserved leucine residue in the midpoint of the second transmembrane domain (M2) of the ligand-activated ion channel family has been proposed to play an important role in receptor activation. In this study, we assessed the importance of this leucine in the activation of rat alpha1beta2gamma2 GABA receptors expressed in Xenopus laevis oocytes by site-directed mutagenesis and two-electrode voltage clamp. The hydrophobic conserved M2 leucines in alpha1(L263), beta2(L259), and gamma2(L274) subunits were mutated to the hydrophilic amino acid residue serine and coexpressed in all possible combinations with their wild-type and/or mutant counterparts. The mutation in any one subunit decreased the EC(50) and created spontaneous openings that were blocked by picrotoxin and, surprisingly, by the competitive antagonist bicuculline. The magnitudes of the shifts in GABA EC(50) and picrotoxin IC(50) as well as the degree of spontaneous openings were all correlated with the number of subunits carrying the leucine mutation. Simultaneous mutation of the GABA binding site (beta2Y157S; increased the EC(50)) and the conserved M2 leucine (beta2L259S; decreased the EC(50)) produced receptors with the predicted intermediate agonist sensitivity, indicating the two mutations affect binding and gating independently. The results are discussed in light of a proposed allosteric activation mechanism.     

Are our universities producing too many PhDs?

As we enter the 21st century, we face a world that will be increasingly dominated by science and technology. More and more jobs will require many of the analytical and thinking skills of a scientist. Citizens everywhere must also become better able to evaluate and understand the judgements of scientific and technical experts when making personal and community decisions. To spread the values and knowledge of science much more widely throughout our societies, we must also spread scientists. Therefore, advanced training in science and the acquisition of important skills through an extensive exposure to research are valuable tools for a wide variety of occupations.     

Isolation and characterization of 23 polymorphic microsatellite loci for a West Indian iguana (Cyclura pinguis) from the British Virgin Islands

Twenty-three polymorphic microsatellite markers were identified and characterized for Cyclura pinguis, a critically endangered species of lizard (Sauria: Iguanidae) native to Anegada Island in the British Virgin Islands. We examined variation at these loci for 39 C. pinguis, finding up to five alleles per locus and an average expected heterozygosity of 0.55. Allele frequency estimates for these microsatellite loci will be used to characterize genetic diversity of captive and wild C. pinguis populations and to estimate relatedness among adult iguanas at the San Diego Zoo that form the nucleus of a captive breeding programme for this critically endangered species.