Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Comparative anatomy and systematics of woody Saxifragaceae. Aphanopetalum Endl.

The floral and vegetative anatomy of the small Australian genus Aphanopetalum were studied. Wood is described for the first time and is characterized by predominantly solitary pores, scalariform vessel element perforation plates with low bar numbers, imperforate tracheary elements with distinctly bordered pits, sparse axial parenchyma, and a combination of homocellular and heterocellular rayS. Starch occurs in both axial and ray parenchyma of the wood. Stems possess unilacunar, one-trace nodes and the uncommon feature of an endodermis with well-defined Casparian stripS. Leaves have anomocytic stomata, a bifacial mesophyll and semicraspedodromous venation or a combination of semicraspedodromous and brochidodromous venation. The tetramerous flowers are apetalous or have minute petals. The compound, half-inferior gynoecium consists of essentially totally united carpels. The pattern of floral vascularization resembles different Saxifragaceae sensu lalo in that the compound sepal-plane and petal-plane traces give rise to staman bundles as well as sepal, petal, and carpel wall venation in their respective planes. The ventral ovarian bundles are fused into a single ventral complex that subdivides at the top of the ovary to form ventral bundles and to supply the one ovule in each locule. Vegetative and floral features provide compelling evidence to suggest that Aphanopetalum has its nearest relatives among the Saxifragaceae sensu lato rather than Cunoniaceae. The genus is probably best treated as forming its own subfamily (or family) among the saxifragaean alliance.     

Molecular evolution of voltage-sensitive ion channel genes: on the origins of electrical excitability

We have analyzed nucleic acid and amino acid sequence alignments of a variety of voltage-sensitive ion channels, using several methods for phylogenetic tree reconstruction. Ancient duplications within this family gave rise to three distantly related groups, one consisting of the Na+ and Ca++ channels, another the K+ channels, and a third including the cyclic nucleotide-binding channels. A series of gene duplications produced at least seven mammalian homologues of the Drosophila Shaker K+ channel; clones of only three of these genes are available from all three mammalian species examined (mouse, rat, and human), pointing to specific genes that have yet to be recovered in one or another of these species. The Shaw-related K+ channels and the Na+ channel family have also undergone considerable expansion in mammals, relative to flies. These expansions presumably reflect the needs of the high degree of physiological and neuronal complexity of mammals. Analysis of the separate domains of the four-domain channels (Ca++ and Na+) supports their having evolved by two sequential gene duplications and implies the historical existence of a functional two-domain channel.      

The Vascular System in the Rachis of a Wheat Ear

The vascular system in the rachis of ears of wheat (Triticumaestivum L. cvs Gamenya, Olympic and Bungulla) was examinedon material grown in the field and in a growth cabinet. In theinternodes, central and peripheral bundles were observed andtheir mean number and size were determined. A significant 1:1 relationship between the number of spikelets on the ear andthe number of central bundles at the base of the rachis wasestablished. The number of both central and peripheral bundlesdeclined acropetally along thé length of the rachis.The decline in peripheral bundles occurred mainly between internodes1 and 6, numbered from the base. The decline in central bundlesoccurred at a rate of less than one bundle per internode betweeninternodes 1 and 4, though in some ears, there was no decline;in larger ears, central bundles declined at a rate of one totwo bundles per internode between internodes 5 and 11. Aboveinternode 11, the rate of decline varied with ear size. Threecentral bundles consistently reached the terminal spikelet.The number and cross-sectional surface area of xylem vesselsand sieve tubes and the total vascular size also declined acropetallyalong the rachis. The decline in total vascular size was dueto (a) some bundles branching and to reductions in size, (b)the diversion or dropping of bundles into spikelets, or (c)a combination of (a) and (b). These observations are discussedin relation to the distribution of grain number and weight onthe ear. Triticum aestivum L., wheat, rachis, spikelets, vascular anatomy, xylem, sieve tubes     

Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae)

Anatomy of leaf, stem, and root of more than 100 species in subtribe Dendrobiinae (Orchidaceae) was studied with the light microscope to provide a comparative anatomical treatment of these organs, to serve as an independent source of evidence that might be taxonomically important, and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our classification on that of Rudolf Schlechter as the most complete and widely accepted today. We found that the anatomy of plants in subtribe Dendrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these anatomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of Dendrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the difficulty of determining the phylogenetic relationships of many of Schlechter's sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications based on available data, be retained for the present, pending a more detailed understanding of the phylogeny of Dendrobiinae based on morphology, micromorphology, anatomy, and DNA studies.