The rep region of pR plasmid regulates the expression of SOS system

Summary By using an artificial hybrid between phage and the pR plasmid, we have shown that the rep region of the pR plasmid encodes a function which regulates the expression of the muc genes (plasmid genes that are under the negative control of lexA and responsible for an increased rate of spontaneous mutagenesis and resistance to UV and chemicals). Expression of the muc genes was monitored by a fusion between the muc promoter and the lacZ structural gene. When E. coli cells containing such a fusion are infected by the hybrid pR phasmid, -galactosidase activity is enhanced, indicating that pR encodes an antagonist of lexA. By deletion mapping we have located the gene encoding the antagonist of lexA (bat) in the rep region of the plasmid. The bat gene product can also antagonize the cI repressor as shown by the observation that pR phasmids are virulent on a homoimmune lysogen. We have exploited this latter property to carry out genetic and functional analysis of the bat region. This region is organized as a classical operon where the expression of the bat structural gene is negatively regulated by a repressor gene that encodes a proteic product.     

Voltage-dependent channels permeable to K+ and Na+ in the membrane ofAcer pseudoplatanus vacuoles

Summary The patch-clamp technique in whole-cell configuration was used to study the electrical properties of the tonoplast in isolated vacuoles fromAcer pseudoplatanus cultured cells. In symmetrical KCl or K₂ malate solutions, voltage- and time-dependent inward currents were elicited by hyperpolarizing the tonoplast (inside negative), while in the positive range of potential the conductance was very small. The specific conductance of the tonoplast at –100 mV, in 100mm symmetrical KCl was about 160 S/cm². The reversal potentials (E _rev) of the current, measured in symmetrical or asymmetrical ion concentrations (cation, anion or both) were very close to the values of the K⁺ equilibrium potential. Experiments performed in symmetrical or asymmetrical NaCl indicate that Na⁺ too can flow through the channels. NeitherE _rev nor amplitude and kinetics of the current changed by replacing NaCl with KCl in the external solution. These results indicate the presence of hyperpolarization-activated channels in tonoplasts, which are permeable to K⁺ as well as to Na⁺. Anions such as Cl^– or malate seem to contribute little to the channel current.     

Tricyclic Imipramine Modification of the Circadian Rhythms of Hypothalamic Serotonin, its Precursors and Acid Catabolite in Individually Housed Rats

Circadian rhythms of serotonin (5HT), its precursors tryptophan (TP) and 5-hydroxy-tryptophan (5HTP) and its acid catabolite 5-hydroxy-indoleacetic acid (5HIAA), were determined in the hypothalamus of control rats and rats which had been treated continuously with subcutaneous imipramine (10 mg/kg/day) for 2 weeks.

Rats were individually housed and entrained to LD12:12. Controls showed the 5HT and TP peaks in the light and dark periods respectively, as reported in the literature, but no inverted correlation (antiphase) between SHT and 5HIAA rhythms.

Imipramine significantly modified circadian rhythm characteristics: the 5HT acrophase was advanced, that of TP and 5HIAA was delayed. Imipramine also significantly increased hypothalamic SHT and TP concentrations.     

The β4Integrin Subunit Is Expressed in Mouse Fibroblasts and Modulated by Transforming Growth Factor-β1

Integrin β₄subunit is present in association with α₆chain on both normal and transformed epithelial cells. Recently α₆β₄heterodimer was found on the endothelium of medium-sized blood vessels and on immature thymocytes. In this report we show, by Northern blotting, indirect immunofluorescence, immunoprecipitation, and Western blotting, that β₄subunit is expressed also on cells of mesenchymal origin such as fibroblasts, myoblasts, and myotubes. Increased expression of α₆β₄has been related to the aggressive metastatic phenotype of human and murine carcinomas. The transforming growth factor β₁(TGF-β₁) has been found to modulate the expression of several integrins and intracellular matrix proteins, as well as to stimulate cell invasion and metastatic potential. To evaluate whether α₆β₄expression is modulated by TGF-β₁, we transfected 3T3 fibroblasts with an expression vector carrying the human TGF-β₁cDNA driven by the SV40 early promoter. We observed by indirect immunofluorescence a modification in the subcellular distribution of β₄subunit, which acquires a perinuclear localization. This finding suggests this integrin subunit correlates with the cytoskeletal reorganization induced by TGF-β₁.     

Open-channel block by internally applied amines inhibits activation gate closure in batrachotoxin-activated sodium channels.

We have studied the action of several pore-blocking amines on voltage-dependent activation gating of batrachotoxin(BTX)-activated sodium channels, from bovine heart and rat skeletal muscle, incorporated into planar lipid bilayers. Although structurally simpler, the compounds studied show general structural features and channel-inhibiting actions that resemble those of lidocaine. When applied to the cytoplasmic end of the channel, these compounds cause a rapid, voltage-dependent, open-channel block seen as a reduction in apparent single-channel amplitude (companion paper). Internal application of phenylpropanolamine, phenylethylamine, phenylmethylamine, and diethylamine, as well as causing open-channel block, reduces the probability of channel closure, producing a shift of the steady-state activation curve toward more hyperpolarizing potentials. These gating effects were observed for both cardiac and skeletal muscle channels and were not evoked by addition of equimolar N-Methyl-D-Glucamine, suggesting a specific interaction of the blockers with the channel rather than a surface charge effect. Kinetic analysis of phenylpropanolamine action on skeletal muscle channels indicated that phenylpropanolamine reduced the closed probability via two separate mechanisms. First, mean closed durations were slightly abbreviated in its presence. Second, and more important, the frequency of the gating closures was reduced. This action was correlated with the degree, and the voltage dependence, of open-channel block, suggesting that the activation gate cannot close while the pore is occluded by the blocker. Such a mechanism might underlie the previously reported immobilization of gating charge associated with local anesthetic block of unmodified sodium channels.