Basolateral membrane potassium conductance of A6 cells

Summary To study the properties of the basolateral membrane conductance of an amphibian epithelial cell line, we have adapted the technique of apical membrane selective permeabilization (Wills, N.K., Lewis, S.A., Eaton, D.C., 1979b, J. Membrane Biol. 45:81–108). Monolayers of A6 cells cultured on permeable supports were exposed to amphotericin B. The apical membrane was effectively permeabilized, while the high electrical resistance of the tight junctions and the ionic selectivity of the basolateral membrane were preserved. Thus the transepithelial current-voltage relation reflected mostly the properties of the basolateral membrane. Under basal conditions, the basolateral membrane conductance was inward rectifying, highly sensitive to barium but not to quinidine. After the induction of cell swelling either by adding chloride to the apical solution or by lowering the osmolarity of the basolateral solution, a large out-ward-rectifying K⁺ conductance was observed, and addition of barium or quinidine to the basolateral side inhibited, respectively, 82.4±1.9% and 90.9±1.0% of the transepithelial current at 0 mV. Barium block was voltage dependent; the half-inhibition constant (K _i) varied from 1499±97 m at 0 mV to 5.7±0.5 m at –120 mV.Cell swelling induces a large quinidine-sensitive K⁺ conductance, changing the inward-rectifying basolateral membrane conductance observed under basal conditions into a conductance with outward-rectifying properties.     

Amplification dynamics of miniature inverted-repeat transposable elements and their impact on rice trait variability

Transposable elements (TEs) are a rich source of genetic variability. Among TEs, miniature inverted-repeat TEs (MITEs) are of particular interest as they are present in high copy numbers in plant genomes and are closely associated with genes. MITEs are deletion derivatives of class II transposons, and can be mobilized by the transposases encoded by the latter through a typical cut-and-paste mechanism. However, MITEs are typically present at much higher copy numbers than class II transposons. We present here an analysis of 103 109 transposon insertion polymorphisms (TIPs) in 738 Oryza sativa genomes representing the main rice population groups. We show that an important fraction of MITE insertions has been fixed in rice concomitantly with its domestication. However, another fraction of MITE insertions is present at low frequencies. We performed MITE TIP-genome-wide association studies (TIP-GWAS) to study the impact of these elements on agronomically important traits and found that these elements uncover more trait associations than single nucleotide polymorphisms (SNPs) on important phenotypes such as grain width. Finally, using SNP-GWAS and TIP-GWAS we provide evidence of the replicative amplification of MITEs.     

Miscanthus Clones Display Large Variation in Floral Biology and Different Environmental Sensitivities Useful for Breeding

A wider range of Miscanthus varieties is required to develop Miscanthus clones that are suitable for bioenergy production. For this reason, breeding programs need to be initiated using knowledge regarding the genetic influence on floral biological traits. The objective of the present study was to characterize the genotypic variation in flowering and panicle architecture traits in Miscanthus by studying (i) the clone effect on these traits and (ii) the clone sensitivity to environmental conditions. The flowering traits characterized were date of panicle emergence, date of flowering onset, and interval between these two traits. The panicle architecture traits characterized were total panicle length, longest panicle raceme size, raceme number per panicle, floral density, and total flower number per panicle. Eight clones were studied in a greenhouse under four environmental conditions including two day lengths (an 8-h short day length and a natural day length) and two temperature treatments (warm and cool). Miscanthus clones showed large differences in flowering and panicle architecture traits. Moreover, day length appeared to be the most important environmental factor creating differential clone sensitivities for the panicle emergence and the onset of flowering in contrast to temperature factor for the total flower number per panicle. In addition, the behavior of the clone Sacc was in contrast with that of the other clones for most of the traits studied. This knowledge will be useful to optimize the synchronization of flowering between Miscanthus clones for more successful breeding programs.     

Regulation of MSH release from the neurointermediate lobe of Xenopus laevis by CRF-like peptides

Immunocytochemical studies showed the presence of a fiber system containing a CRF-like peptide in the median eminence and in the neural lobe of the pituitary gland of Xenopus laevis. During in vitro superfusion of neurointermediate lobe tissue, CRF, sauvagine and urotensin I induced a rapid and dose-dependent stimulation of secretion of MSH and endorphin. Tissue of white-background adapted animals displayed a remarkably higher sensitivity to CRF and sauvagine than tissue from animals that were adapted to a black background. During superfusion of isolated melanotrope cells in suspension, it was shown that CRF and sauvagine exerted their effect directly on the melanotrope cell. We therefore conclude that there is morphological and biochemical evidence to consider a CRF-like peptide as a physiological MSH-releasing factor.     

Prolonged exposure of J-774 macrophages to gamma-killedMycobacterium avium did not affect their inability to check the intracellular growth of viableM. avium

J-774 murine macrophages were allowed to multiply in the presence of gammairradiated (4.5×10⁶ rads)Mycobacterium avium for 3 days. The macrophages thus stimulated and still containing killed bacteria were then challenged with viableM. avium bacteria, and the intracellular growth of these bacilli was measured during 1 week by lysing the J-774 cells and measuring the viable bacterial counts on 7H10 ager. The results were compared with those obtained in parallel with normal J-774 cells. Our results showed that pretreatment of macrophages with killedM. avium neither enhanced their capacity to check the intracellular growth of viableM. avium nor did it potentiate the intracellular activity of rifampicin, ansamycin and clofazimine against actively multiplyingM. avium.