Frequency-dependent effect of verapamil on rat soleus muscle

Summary In the presence of verapamil (0.1 mM) rat soleus muscle fibers failed to generate action potentials with overshoots. In fibers with their V_m set to a local level of –90 mV, verapamil produces a gradual reduction in the amplitude of the repetitive action potentials; this effect is more pronounced at high rates of stimulation (100 Hz). Our results suggest a local anesthetic action of this drug that could contribute with its calcium channel blocking effect to the diminished mechanical tension observed in the presence of the drug.Acknowledgments. We thank A. Losavio and M. Stefanolo for technical assistance. This work was supported by grants from CONICET and SUBCYT, Buenos Aires, Argentina and Muscular Dystrophy Association, USA.     

Defining the resistance to oxygen transfer in tissue hypoxia

Studies of O2 supply in freshly isolated adult mammalian cells provide new insight into the factors that limit mitochondrial oxygenation in vivo. Of particular importance, mitochondria are present at high densities and often in apparent clusters, both of which contribute to local O2 gradients under hypoxic conditions. Current evidence indicates that the mitochondrial distribution is a component of the differentiated phenotype of adult mammalian cells and that specific motors and anchoring mechanisms are present to allow redistribution in response to developmental, physiological and pathological challenges. To compare the importance of resistance to O2 transfer under different conditions and at different sites along the supply path in vivo, a simple mathematical expression of relative resistance to O2 supply is introduced. Under various pathophysiological conditions, this resistance increases in specific regions of the pulmonary, circulatory or cellular supply path and results in O2 deficiency in the mitochondria. Regardless of cause, the relative resistance increases dramatically in the vicinity of mitochondrial clusters during hypoxia.     

Interpretation of Fashion Change through the Thoughts of Hong Kong Young Consumers

Fashion changes frequently, on monthly, seasonal to yearly basis. In different periods of time, people tried to use different theories to explain the concept of fashion change. Traditional views including trickle down theory, collective selection theory, mass market theory and subculture leadership theory. From the viewpoint of contemporary thoughts, symbolic interactionist theory of fashion and the power of the fashion industry were discussed and used to examine fashion images prevailing in Hong Kong. Hong Kong young consumers were selected as study samples. Focus group interviews and questionnaire survey were used as qualitative and quantitative method. Results shows that to accept fashion change, status (working or studying) had influence in interpreting fashion images. In addition, male and female students had different opinion on selected statements of the symbolic interactionist theory of fashion but no difference was found between working subjects. Marketing implications are discussed with refere     

Munc13-1 is essential for fusion competence of glutamatergic synaptic vesicles.

Neurotransmitter release at synapses between nerve cells is mediated by calcium-triggered exocytotic fusion of synaptic vesicles. Before fusion, vesicles dock at the presynaptic release site where they mature to a fusion-competent state. Here we identify Munc13-1, a brain-specific presynaptic phorbol ester receptor, as an essential protein for synaptic vesicle maturation. We show that glutamatergic hippocampal neurons from mice lacking Munc13-1 form ultrastructurally normal synapses whose synaptic-vesicle cycle is arrested at the maturation step. Transmitter release from mutant synapses cannot be triggered by action potentials, calcium-ionophores or hypertonic sucrose solution. In contrast, release evoked by alpha-latrotoxin is indistinguishable from wild-type controls, indicating that the toxin can bypass Munc13-1-mediated vesicle maturation. A small subpopulation of synapses of any given glutamatergic neuron as well as all synapses of GABA (gamma-aminobutyric acid)-containing neurons are unaffected by Munc13-1 loss, demonstrating the existence of multiple and transmitter-specific synaptic vesicle maturation processes in synapses.     

DNA-dependent protein kinase is not required for the p53-dependent response to DNA damage.

Damage to DNA in the cell activates the tumour-suppressor protein p53, and failure of this activation leads to genetic instability and a predisposition to cancer. It is therefore crucial to understand the signal transduction mechanisms that connect DNA damage with p53 activation. The enzyme known as DNA-dependent protein kinase (DNA-PK) has been proposed to be an essential activator of p53, but the evidence for its involvement in this pathway is controversial. We now show that the p53 response is fully functional in primary mouse embryonic fibroblasts lacking DNA-PK: irradiation-induced DNA damage in these defective fibroblasts induces a normal response of p53 accumulation, phosphorylation of a p53 serine residue at position 15, nuclear localization and binding to DNA of p53. The upregulation of p53-target genes and cell-cycle arrest also occur normally. The DNA-PK-deficient cell line SCGR11 contains a homozygous mutation in the DNA-binding domain of p53, which may explain the defective response by p53 reported in this line. Our results indicate that DNA-PK activity is not required for cells to mount a p53-dependent response to DNA damage.     

A family of mammalian Na+-dependent L-ascorbic acid transporters.

Vitamin C (L-ascorbic acid) is essential for many enzymatic reactions, in which it serves to maintain prosthetic metal ions in their reduced forms (for example, Fe2+, Cu+), and for scavenging free radicals in order to protect tissues from oxidative damage. The facilitative sugar transporters of the GLUT type can transport the oxidized form of the vitamin, dehydroascorbic acid, but these transporters are unlikely to allow significant physiological amounts of vitamin C to be taken up in the presence of normal glucose concentrations, because the vitamin is present in plasma essentially only in its reduced form. Here we describe the isolation of two L-ascorbic acid transporters, SVCT1 and SVCT2, from rat complementary DNA libraries, as the first step in investigating the importance of L-ascorbic acid transport in regulating the supply and metabolism of vitamin C. We find that SVCT1 and SVCT2 each mediate concentrative, high-affinity L-ascorbic acid transport that is stereospecific and is driven by the Na+ electrochemical gradient. Despite their close sequence homology and similar functions, the two isoforms of the transporter are discretely distributed: SVCT1 is mainly confined to epithelial systems (intestine, kidney, liver), whereas SVCT2 serves a host of metabolically active cells and specialized tissues in the brain, eye and other organs.     

Unidirectional rotary motion in a molecular system.

The conversion of energy into controlled motion plays an important role in both man-made devices and biological systems. The principles of operation of conventional motors are well established, but the molecular processes used by 'biological motors' such as muscle fibres, flagella and cilia to convert chemical energy into co-ordinated movement remain poorly understood. Although 'brownian ratchets' are known to permit thermally activated motion in one direction only, the concept of channelling random thermal energy into controlled motion has not yet been extended to the molecular level. Here we describe a molecule that uses chemical energy to activate and bias a thermally induced isomerization reaction, and thereby achieve unidirectional intramolecular rotary motion. The motion consists of a 120 degrees rotation around a single bond connecting a three-bladed subunit to the bulky remainder of the molecule, and unidirectional motion is achieved by reversibly introducing a tether between the two units to energetically favour one of the two possible rotation directions. Although our system does not achieve continuous and fast rotation, the design principles that we have used may prove relevant for a better understanding of biological and synthetic molecular motors producing unidirectional rotary motion.