Birefringence changes in vertebrate striated muscle

The changes in birefringence in the rigor to relax transition of single Triton-extracted rabbit psoas muscle fibers have been investigated. The total birefringence of rigor muscle fibers was dependent on sarcomere length and ranged from (1.46 ± 0.08) × 10⁻³ to (1.60 ± 0.06) ± 10⁻³ at sarcomere lengths from 2.70 μm to 3.40 μm. An increase in total birefringence was measured dependent on sarcomere length when 55 single fibers were relaxed from the rigor state with Mg-ATP. Pyrophosphate relaxation produced a smaller increase in retardation when compared to Mg-ATP. The expected change in intrinsic birefringence during the rigor to relax transition was calculated assuming a hinge function of the subfragment 2 moiety of myosin. The changes in birefringence during isometric contraction and relaxation have been discussed in relation to possible structural changes.     

AGE VARIATIONS IN CORTICAL MEMBRANES OF ROTIFERS

Electron micrographs were made of rotifers of known ages embedded in Vestopal and stained with lead hydroxide. In epithelial cells lining the gut of the rotifer, anatomical continuity is seen between the cell membrane, the cortical membranes, and the rough endoplasmic reticulum at the basal region of the cells. At their luminal surface, these cells possess a terminal web, and colloidal gold is taken up via food vacuoles at this surface. Such pinocytosis does not occur on the peripheral or distal surface (pseudocoelomic) of these cells. Exposure of rotifers to adenine inhibits the formation of cortical infoldings of the cell membrane and the formation of the rough reticulum, whereas the ribosomes and the Golgi apparatus appear to be unaffected. The suggestion is made that the rough reticulum may be derived from modifications of the cell membrane and that the rate of formation of the rough reticulum in adult and elderly rotifers is lower than in the actively growing animal.     

Molecular phylogeny of the springhare, Pedetes capensis, based on mitochondrial DNA sequences

The phylogenetic position of the Pedetidae, represented by a single species Pedetes capensis, is controversial, reflecting in part the retention of both Hystricomorphous and Sciurognathous characteristics in this rodent. In an attempt to clarify the species evolutionary relationships, mtDNA gene sequences from 10 rodent species (representing seven families) were analyzed using phenetic, parsimony, and maximum-likelihood methods of phylogenetic inference; the rabbit, Oryctolagus cuniculus (Order Lagomorpha), and cow, Bos taurus (Order Artiodactyla), were used as outgroups. Investigation of 714 base pairs of the protein-coding cytochrome b gene indicate strong base bias at the third codon position with significant rate heterogeneity evident between the three structural domains of this gene. Similar analyses conducted on 816 base pairs of the 12S rRNA gene revealed a transversion bias in the loop sections of all taxa. The cytochrome b gene sequences proved useful in resolving associations between closely related species but failed to produce consistent tree topologies at the family level. In contrast, phylogenetic analysis of the 12S rRNA gene resulted in strong support for the clustering of Pedetidae/Heteromyidae/Geomyidae and Muridae in one clade to the exclusion of the Hystricidae/Thryonomyidae and Sciuridae, a finding which is concordant with studies of rodent fetal membranes as well as reproductive and other anatomical features.      

FINE STRUCTURE OF THE CILIA OF ROTIFERS

The fine structure of the coronal cilia of the rotifer Philodina citrina has been studied in detail. Specimens were fixed with OsO₄ and embedded in butyl—methyl methacrylate, Epon 812, or Vestopal and sectioned with a Porter-Blum microtome. The details of structure of the rootlets, basal bodies, basal plates, and free cilia are described. The general structure of the rotifer ciliary apparatus conforms well to that established for other species. One of the main observations is the difference in structure of the peripheral filaments in the opposing halves of a cross-section of the free cilium. Also, in longitudinal sections evidence is offered for the existence of a helical structure in the peripheral filaments.     

Improvements on the Prescott-Jones method for the colorimetric analysis of ureido compounds

The colorimetric assay procedure of Prescott and Jones ((1969) Anal. Biochem.32, 408–419) has been modified to make the standard curve more consistently linear. Improved results are obtained when the assay tubes are exposed to yellow light at an intensity of 45–50 fc (480–540 lx) during color development. Somewhat longer incubation times are required for color development with yellow light.