Leiurus quinquestriatus venom inhibits different kinds of Ca2+-dependent K+ channels

A minor protein component of Leiurus quinquestriatus venom has been reported to inhibit selectively the apamin-insensitive Ca2+-dependent K+ channels of mammalian skeletal muscle (Miller, C., Moczydlowski, E., Latorre, R. and Phillips, M. (1985) Nature 313, 316-318). We report the effect of the venom on both the apamin-insensitive channels of the human erythrocyte, the Ehrlich cell and the rat thymocyte and the apamin-sensitive channel of the guinea pig hepatocyte. The venom inhibited Ca2+-dependent K+ transport in all the cases with a Ki value within the range of 1 to 10 micrograms/ml, similar to that reported previously in muscle. Valinomycin-induced K+ transport was also antagonized by the venom but its sensitivity was about 1/10 as much as that of the Ca2+-dependent K+ channel.     

Effects of microcin B17 on microcin B17-immune cells

When microcin B17-immune cells are treated with microcin B17 they show many of the physiological effects displayed by microcin B17-sensitive cells treated in the same way. DNA replication stops immediately and several SOS functions are subsequently induced. In sensitive cells these effects are irreversible and lead to cell death, whereas in immune cells they are reversible and there is no loss of viability. This is an unusual mechanism of immunity because it does not prevent the primary action of the microcin. The implications of this mechanism concerning the mode of action of microcin B17 and the induction of the SOS system are discussed.     

Quantitative measurement of smooth muscle shortening in isolated pig trachea

Matched porcine tracheal rings were exposed to theophylline and increasing doses of carbachol in Krebs solution. Histological sections of each ring were traced and each of the following dimensions measured: the external perimeter (Pe) and external area (Ae) defined by the outer border of smooth muscle and inner surface of cartilage, and the internal perimeter (Pi) and internal area (Ai) defined by the luminal surface of the epithelium and the muscle length (L) along its outer border. Absolute wall area (WA = Ae - Ai) and relative wall area (PW = WA/Ae) were calculated. Carbachol-treated tracheal ring dimensions were compared with those of their matched theophylline-treated rings. In tracheal rings with intact cartilage, maximal smooth muscle shortening of 44% was achieved with 10(-2) M carbachol. In tracheal rings in which anterior and posterior segments of cartilage were excised, the trachealis muscle passively shortened by 20% and maximal shortening (10(-3) M carbachol) was 57%. Although Ai decreased with maximal smooth muscle shortening, there were no changes in the length of Pi or in WA. These data show that the cartilage in the porcine trachea exerts both a preload that passively stretches the trachealis muscle and an afterload that limits maximal smooth muscle shortening.     

High-frequency conversion to a "fluffy" developmental phenotype in Aspergillus spp. by 5-azacytidine treatment: evidence for involvement of a single nuclear gene.

Transient exposure of mycelia from Aspergillus niger and Aspergillus nidulans to the cytidine analog 5-azacytidine, leading to no more than 0.3 to 0.5% substitution for cytosine by 5-azacytosine in A. nidulans DNA, resulted in the conversion of a high fraction of the cell population (more than 20%) to a mitotically and meiotically stable "fluffy" developmental phenotype. The phenotypic variants are characterized by the developmentally timed production of a profuse fluffy network of undifferentiated aerial hyphae that seem to escape signals governing vegetative growth. Genetic analysis with six different fluffy clones reveals that this trait is not cytoplasmically coded, is recessive in heterozygous diploids but codominant in heterokaryons, and exhibits a 1:1 Mendelian segregation pattern upon sexual sporulation of heterozygous diploids. Complementation and mitotic haploidization studies indicated that all variants are affected in the same gene, which can be tentatively located on chromosome VIII of A. nidulans. Molecular analysis to search for modified bases showed that DNA methylation is negligible in in both A. niger and A. nidulans and that no differences could be detected among DNAs from wild-type cells, fluffy clones, or mycelia exposed to 5-azacytidine. It thus appears that high-frequency conversion of fungal mycelia to a stable, variant developmental phenotype by 5-azacytidine is the result of some kind of target action on a single nuclear gene and that this conversion can occur in organisms virtually devoid of DNA methylation.     

CORRELATED BIOCHEMICAL AND ULTRASTRUCTURAL CHANGES IN NITROGEN-STARVED EUGLENA GRACILIS1

Growth of Euglena gracilis Z Pringsheim under photoheterotrophic conditions in a nitrogen-deprived medium resulted in progressive loss of chloroplastic material until total bleaching of the cells occurred. Biochemical analysis and ultrastructural observation of the first stages of the starvation process demonstrated an early lag phase (from 0 to 9 h) in which cells increased in size, followed by a period of cell division, apparently supported by the mobilization of some chloroplastic proteins such as the photosynthetic CO₂-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. The degradation of the enzyme started after 9 h of starvation and was preceded by a transient concentration of this protein in pyrenoidal structures. Protein nitrogen and photosynthetic pigments as well as number of chloroplasts per cell decreased during proliferation through mere distribution among daughter cells. However, after 24 h, when cell division had almost ceased, there was a slow but steady decline of photosynthetic pigments. This was paralleled by observable ultrastructural changes including progressive loss of chloroplast structure and accumulation of paramylon granules and lipid globules in the cytoplasm. These findings reinforce the role of chloroplastic materials as a nitrogen source during starvation of E. gracilis in a carbon-rich medium. The excess of ribulose-1,5-bisphosphate carboxylase/oxygenase acts as a first reservoir that, once exhausted, is superseded by the generalized disassembly of the photosynthetic structures, if the adverse environment persists more than 24 h.