THE PHYSICAL AND CHEMICAL ENVIRONMENT OF THE DEVELOPING EMBRYO OF PINUS RESINOSA

The relationship between changes in soluble protein, hexose sugar, total lipid concentration, and osmotic potential occurring in gametophytic supernatant of Pinus resinosa Ait. during in vivo embryogenesis was measured. The effects of varying sucrose levels of culture medium on in vitro embryo and gametophyte development were examined. Increases in embryo volume, and fresh and dry weight of the female gametophyte during in vivo embryogenesis coincide with increasing levels of soluble protein, hexose sugar, and total lipid in the gametophytic supernatant. In contrast, osmotic potential of the supernatant increased only slightly between the zygote and proembryo stages of embryo development, and remained constant thereafter. Gametophytes plus embryos grown in vitro achieved dry weights approaching those of in ovulo gametophytes on media containing levels of sucrose up to 21%. Gametophytes on media with sucrose concentrations up to 21% also resembled normal in ovulo gametophytes in appearance. However, embryo development appeared to be suspended on treatment media containing from 9% to 21% sucrose, while embryos degenerated on media with constant sucrose levels of 3% and 6%. A treatment medium containing approximately 12% sucrose would provide an osmotic environment that duplicates that found in ovulo. While greater sucrose levels promoted more normal gametophyte development in Pinus resinosa, we failed to achieve complete development of the embryo in vitro. Conclusions and implications drawn from these results are discussed.     

Respiratory function of velopharyngeal constrictor muscles during wakefulness in normal adults

Launois, Sandrine H., Judy Tsui, and J. Woodrow Weiss.Respiratory function of velopharyngeal constrictor muscles during wakefulness in normal adults. J. Appl.Physiol. 82(2): 584-591, 1997.The levator velipalatini (LVP) and the superior pharyngeal constrictor (SPC) influencevelopharyngeal patency and soft palate position, but their behaviorduring respiration is incompletely characterized. To further clarifytheir respiratory function, we recorded electromyographic activity(EMG) in the LVP and the SPC in awake normal subjects breathing orally.EMG data were obtained in six subjects for the LVP and in nine subjectsfor the SPC. EMG activity and timing and ventilation were measuredduring isocapnic hypoxia and hyperoxic hypercapnia. Phasic EMG activitywas inconsistently present during unstimulated oral breathing. Timingof EMG phasic activity was variable for both muscles. Peak LVP activitywas mainly or exclusively expiratory in three of six subjects. Peak SPCactivity was mainly or exclusively expiratory in five of nine subjects.With chemostimulation, recruitment of phasic activity was observed inthe LVP in four of six subjects and in the SPC in five of ninesubjects. Tonic activity increased in four of six subjects for the LVPand in three of nine subjects for the SPC. However, the response wasalinear, and intersubject as well as breath-to-breath variability wassubstantial. In conclusion, LVP and SPC are characterized by the highinter- and intrasubject variability of EMG activity, timing ofactivation, and response to chemostimulation.

     

Amino acid concentrations and selected enzyme activities in rat auditory,olfactory, and visual systems

Homogenates of specific brain regions of three sensory systems (auditory, olfactory, and visual) were prepared from pigmented Long-Evans Hooded rats and assayed for amino acid concentrations and activities of glutaminase, aspartate aminotransferase (total, cytosolic, and, by difference, mitochondrial), malate dehydrogenase, lactate dehydrogenase, and choline acetyltransferase. Comparing the quantitative distributions among regions revealed significant correlations between AAT and aspartate, between glutaminase and glutamate, between glutamate and glutamine, and between AAT plus glutaminase, or glutaminase alone, and the sum of aspartate, glutamate, and GABA, suggesting a metabolic pathway involving the synthesis of a glutamate pool as precursor to aspartate and GABA. Of the inhibitory transmitter amino acids, GABA concentrations routinely exceeded those of glycine, but glycine concentrations were relatively high in brainstem auditory structures.     

Nucleotide sequence of Rattus norvegiens mitochondrial DNA that includes the genes for tRNAile, tRNAgln and tRNAf-met

The nucleotide sequence of a segment of mtDNA from Rattus norvegiens (rat) which contains the genes for tRNA^ile, tRNA^gl and tRNA^f-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNA^ile, tRNA^gln and tRNA^f-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.     

Nucleotide sequence variants of Rattus norvegicus mitochondrial DNA

The mitochondrial DNA (mtDNA) molecules of different albino, domesticated rats (Rattus norvegicus) of the SASCO colony are of two kinds (SASCO-1 and SASCO-2) in regard to their sensitivity at certain sites to a number of restriction enzymes. MtDNA molecules from Utah wild R. norvegicus (Wild-UT) have sensitivities to restriction enzymes which differ at some sites from either SASCO-1 or SASCO-2 mtDNA molecules. Four single nucleotide differences were found among the HindIII F fragments (169 nucleotides) of SASCO-1, SASCO-2, and Wild-UT mtDNAs. Arguments are presented in favor of the interpretation that each variant nucleotide is the third nucleotide of the codon containing it, and that none of the four differences would result in a difference in the respective amino acid translated.Dedicated to Professor W. Beermann on the occasion of his 60th birthday     

siRNA-directed inhibition of HIV-1 infection

RNA interference silences gene expression through short interfering 21 23-mer double-strand RNA segments that guide mRNA degradation in a sequence-specific fashion. Here we report that siRNAs inhibit virus production by targeting the mRNAs for either the HIV-1 cellular receptor CD4, the viral structural Gag protein or green fluorescence protein substituted for the Nef regulatory protein. siRNAs effectively inhibit pre- and/or post-integration infection events in the HIV-1 life cycle. Thus, siRNAs may have potential for therapeutic intervention in HIV-1 and other viral infections.     

Mercuric chloride inhibits the in vitro uptake of glutamate in GLAST- and GLT-1-transfected mutant CHO-K1 cells

Glutamate is removed mainly by astrocytes from the extracellular fluid via high-affinity astroglial Na⁺-dependent excitatory amino acid transporters, glutamate/aspartate transporter (GLAST), and glutamate transporter-1 (GLT-1). Mercuric chloride (HgCl₂) is a highly toxic compound that inhibits glutamate uptake in astrocytes, resulting in excessive extracellular glutamate accumulation, leading to excitotoxicity and neuronal cell death. The mechanisms associated with the inhibitory effects of HgCl₂ on glutamate uptake are unknown. This study examines the effects of HgCl₂ on the transport of ³H-d-aspartate, a nonmetabolizable glutamate analog, using Chinese hamster ovary cells (CHO) transfected with two glutamate transporter subtypes, GLAST (EAAT1) and GLT-1 (EAAT2), as a model system. Additionally, studies were undertaken to determine the effects of HgCl₂ on mRNA and protein levels of these transporters. The results indicate that (1) HgCl₂ leads to significant (p<0.001) inhibition of glutamate uptake via both transporters, but is a more potent inhibitor of glutamate transport via GLAST and (2) the effect of HgCl₂ on inhibition of glutamate uptake in transfected CHO cells is not associated with changes in transporter protein levels despite a significant decrease in mRNA expression; thus, (3) HgCl₂ inhibition is most likely related to its direct binding to the functional thiol groups of the transporters and interference with their uptake function.