Evidence for a role of NA+/H+ exchange in platelets activated with calcium-ionophore A 23187

We have investigated the release of protons from human platelets and platelet aggregation induced by the calcium ionophore, A 23187. Addition of the ionophore to suspensions of washed platelets resulted in fast liberation of H+. In the presence of 0.2 mM amiloride, a potent inhibitor of Na+/H+ countertransport, the amount of protons liberated was decreased by 50% and was further reduced to about 10% by 1 mM amiloride. Similar inhibition of H+-release was observed after decreasing Na+ in the incubation medium. Both results suggest that increasing internal Ca2+ by the ionophore induces Na+/H+ exchange in human platelets. Platelet aggregation could be induced by adding the ionophore to the platelet suspension. This aggregation was inhibited by amiloride, at least when induced by low ionophore concentrations. The results suggest that stimulation of Na+/H+ exchange, and the concomitant increase in intraplatelet pH, are important mechanisms in platelet activation.     

Gas mixing in the airways of dog lungs during high-frequency ventilation

Washout of insoluble inert test gases of different diffusivity (He and SF6 or He and Ar) from dog lungs was studied during high-frequency ventilation (HFV). Test gas equilibrium and subsequent washout were performed with HFV, succeeding measurements being performed at different stroke volumes (1.5-2.5 ml/kg body wt), oscillation frequencies (10-30 Hz), and with different lung volumes (32-74 ml X kg-1). Test gas concentrations were continuously measured by a mass spectrometer. The time course of washout could be described as the sum of two exponentials. There were no consistent differences in the time courses of washout between He and SF6 or between He and Ar. It is concluded that gas mixing in the airways during HFV is not significantly limited by diffusion, and this is suggested to apply during HFV to steady-state transport of respiratory gases (e.g., O2 and CO2) as well as to the transient state of inert gas washout.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Requirement of N-terminal amino acid residues of gp41 for human immunodeficiency virus type 1-mediated cell fusion.

An expression vector was designed to test the structural requirements of the gp41 N terminus for human immunodeficiency virus type 1-induced membrane fusion. Mutations in the region coding for the N terminus of gp41 were found to disrupt glycoprotein expression because of deleterious effects on the Rev-responsive element (RRE). Insertion of an additional RRE in the 3'-noncoding sequence of env made possible efficient glycoprotein expression, irrespective of the mutations introduced into the RRE in the natural location. This permitted the insertion of the unique restriction site SpeI within the N-terminal sequences of gp41, allowing convenient and efficient mutation of the gp41 N terminus by using double-stranded synthetic oligonucleotides. Mutants with deletions of 1 to 7 amino acids of the N terminus were constructed. Expression and cleavage of all mutants were confirmed by Western immunoblot analysis with anti-gp41 antibodies. The capability of mutants to induce membrane fusion was monitored following transfection of HeLa-T4+ cell lines with wild-type and mutant expression vectors by electroporation and microinjection. The efficiency of cell-fusing activity decreased drastically with deletion of 3 and 4 amino acids and was completely lost with deletion of 5 amino acids. Cotransfection of the parent and mutant expression vectors resulted in reduced cell-fusing activity. The extent of this dominant interference by mutant glycoprotein paralleled the decrease in cell-fusing activity of the mutants alone. This suggests the existence of a specific N-terminal structure required for fusing activity. However, there does not appear to be a stringent requirement for the precise length of the N terminus. This finding is supported by the length variation of this region among natural human immunodeficiency virus type 1 isolates and is in contrast to the apparent stringency in the length of analogous N-terminal structures of influenza A virus and paramyxovirus fusion glycoproteins.