4-Aminopyridine: Effects on electrical activity during ischemia and reperfusion in perfused rat hearts

We investigated the effects of 2 and 4 mM 4-aminopyridine (4-AP, – blocker of the transient outward current I_to) on the electrophysiological response to regional ischemia and reperfusion. Spontaneously beating rat hearts were subjected to coronary occlusion (10 min) followed by reperfusion. The surface electrogram and the membrane potential from subepicardial left ventricular cells were recorded throughout. The basal effect of 4-AP was a dose dependent increase in the action potential duration (APD₉₀) without changes in the resting potential or the heart rate. During early ischemia resting depolarization (from 87.4 ± 1.9–70.1 ± 2.5 mV in the controls) was enhanced by 4 mM, 4-AP (84.3 ± 1.4 mV vs. 61.7 ± 1.3 mV) whereas APD₉₀ increased by 73.5%. These effects resulted in a marked reduction in the duration of diastolic intervals that led to conduction failure and aborted responses. A partial recovery was found by the end of ischemia concomitant with APD₉₀ shortening in both, control and 4-AP treated hearts. On reperfusion, 4-AP did not influence the initial incidence of ventricular tachyarrhythmias but decreased their duration from 531.5 ± 56.3–260.7 ± 100 sec (2 mM) and to 75.6 ± 10.5 sec (4 mM). These data confirm others obtained by Henry et al. [11] in isolated cells indicating that ischemia induces sequential changes in several K⁺ conductances. In addition, they show that changes in action potential characteristics may exert beneficial effects on reperfusion arrhythmias by acting on the arrhythmic substrate without suppressing the trigger mechanism.     

Regulation of glucose transport by insulin and non-hormonal factors

Glucose uptake by nucleated cells is mediated by facilitated diffusion. In adipocytes, fibroblasts and muscle fibers uptake is regulated by a variety of hormones, environmental factors, and metabolic conditions. Glucose uptake by mammalian red cells also occurs by facilitated diffusion, but is not regulated by the same factors and conditions as in nucleated cells; yet the pharmacological and selectivity properties of this transport system resemble those of glucose uptake in regulated cells. The glucose transporter in the human red cell is a 55, 000 dalton protein, which has been purified to homogeneity and functionally reconstituted in artificial systems. Little is known about the molecular identity of the sugar carrier in other cell types. Glucose uptake is stimulated by insulin in muscle, fat and skin cells but not in bone, brain, placenta, erythrocytes nor probably lymphocytes. In responsive cells, stimulation occurs within seconds of exposure to the hormone; it requires cellular integrity but once elicited, it persists in isolated membranes; protein synthesis is not required for either the onset of the response or the return to basal conditions after hormone removal; on the other hand, intracellular energy is required for both steps; the cytoskeleton does not seem to be involved in the regulation of glucose uptake by insulin. In general, insulin increases V_t while K_t is unaffected. The hormone could affect the rate of turnover of the transporter in the membrane, and/or the number of transporters active at any time. An increase in the number of transport sites in the plasma membrane, due to incorporation of additional sites originating from intracellular membranes, has recently been proposed on the basis of both ³H-cytochalasin B binding and glucose transport determinations in isolated plasma and intracellular membranes. The feasibility and implications of a rapid and reversible translocation of glucose transport sites from specific intracellular pools to the plasma membrane are discussed.     

Insulin and hypertonicity recruit GLUT4 to the plasma membrane of muscle cells by using N-ethylmaleimide-sensitive factor-dependent SNARE mechanisms but different v-SNAREs: role of TI-VAMP

Insulin and hypertonicity each increase the content of GLUT4 glucose transporters at the surface of muscle cells. Insulin enhances GLUT4 exocytosis without diminishing its endocytosis. The insulin but not the hypertonicity response is reduced by tetanus neurotoxin, which cleaves vesicle-associated membrane protein (VAMP)2 and VAMP3, and is rescued upon introducing tetanus neurotoxin-resistant VAMP2. Here, we show that hypertonicity enhances GLUT4 recycling, compounding its previously shown ability to reduce GLUT4 endocytosis. To examine whether the canonical soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) mechanism is required for the plasma membrane fusion of the tetanus neurotoxin-insensitive GLUT4 vesicles, L6 myoblasts stably expressing myc-tagged GLUT4 (GLUT4myc) were transiently transfected with dominant negative N-ethylmaleimide-sensitive factor (NSF) (DN-NSF) or small-interfering RNA to tetanus neurotoxin-insensitive VAMP (TI-VAMP siRNA). Both strategies markedly reduced the basal level of surface GLUT4myc and the surface gain of GLUT4myc in response to hypertonicity. The insulin effect was abolished by DN-NSF, but only partly reduced by TI-VAMP siRNA. We propose that insulin and hypertonicity recruit GLUT4myc from partly overlapping, but distinct sources defined by VAMP2 and TI-VAMP, respectively.     

Effects of sodium fluoride on the mechanical activity in mouse gastric preparations

The aim of the present study was to investigate the responses induced by sodium fluoride (NaF) on gastric mechanical activity, using mouse whole-stomach preparations. The mechanical activity was recorded in vitro as changes of intraluminal pressure. In most of the preparations, NaF induced a tetrodotoxin-insensitive biphasic effect characterized by early relaxation followed by slowly developing contractile response. The contraction was dependent on the concentration of NaF, whereas the relaxation was observed at only 10-30 mmol/L NaF. The contractile effect was significantly reduced by nifedipine (an L-type Ca(2+) channel blocker), ryanodine or ruthenium red (inhibitors of Ca(2+) release from sarcoplasmic reticulum), and GF109203X (a protein kinase C inhibitor). Moreover, it was abolished by neomycin (an inhibitor of phospholipase C) and potentiated by SQ22536 (an inhibitor of adenylyl cyclase). All the drugs significantly increased the relaxation, except SQ22536, which abolished it. The present results suggest that NaF causes a complex mechanical response in the whole-stomach, which might explain gastric discomfort after fluoride ingestion. The relaxation appears owing to production of cAMP, while the contractile effects imply activation of phospholipase C, protein kinase C, influx of Ca(2+), and release of Ca(2+) from ryanodine-sensitive intracellular store.     

Isolation, screening and characterization of bacteriocin-producing lactic acid bacteria isolated from traditional fermented food

100 lactic acid bacterial strains isolated from traditional fermented foods (yoghurt, milk cream, sour dough and milk) were screened for bacteriocin production. Twenty six strains producing a nisin-like bacteriocin were selected. Most of these isolates gave only a narrow inhibitory spectrum, although one showed a broad inhibitory spectrum against the indicator strains tested, this strain was determined as Lactococcus lactis. The influence of several parameters on the fermentative production of nisin by Lactococcus lactis was studied. Production of nisin was optimal at 30 degrees C and in the pH range 5.5-6.3. The effect of different sulphur and nitrogen sources on Lactococcus lactis growth and nisin production was studied. Magnesium sulfate and manganese sulfate were found to be the best sulphur sources while triammonium citrate was the best inorganic nitrogen source and meat extract, peptone and yeast extract were the best organic nitrogen source for nisin production.     

Proliferation response of leukemic cells to CD70 ligation oscillates with recurrent remission and relapse in a low-grade lymphoma

Interactions of the TNF-related cell surface ligand CD70 with its receptor CD27 provide a costimulatory signal in B and T cell activation. Functional CD70-CD27 interactions could contribute to lymphoma and leukemia progression. This possibility was studied using DNA microarrays on a unique case of low-grade lymphoma/leukemia characterized by recurrent cycles of acute leukemic phase alternating with spontaneous remission. Upon induction of the acute phase expression of CD70 and CD27 in the leukemic cells increased 38- and 25-fold, respectively. Coexpression of membrane CD70 and CD27 on the leukemic (CD5+CD19+) cells was maximal 2-3 days following initiation of the attack. Soluble CD27 in the patient's serum was elevated during remission and further increased in the attack. Functional tests showed that neither anti-CD70 nor anti-CD27 Abs affect the rate of apoptosis. However, the anti-CD70 Ab specifically enhanced proliferation of the remission phase leukemic cells, whereas proliferation of the acute-phase counterparts that express higher level of membrane CD70 was unaffected. Hence, in this lymphoma/leukemia, membrane CD70 is presented on the leukemic cells in a responsive state during the remission and a nonresponsive state during the attack. Presumably, CD70 in its responsive state provides a costimulatory receptor for initiating the next acute phase while its nonresponsive state enables the remission.     

On the biogenesis of marine isoprenoids

The isoprenoids comprise an important group among the marine natural products which are mainly obtained from soft corals, sponges and algae. The cembranes, xenia metabolites from soft corals and rearranged spongans from sponges are examples of marine diterpenoids obtained directly from GeGePP or after remarkable changes. Biogenesis, suggested biosynthesis, based on the structure and mainly known terrestrial biosynthesis, is proposed for diterpenoids and higher isoprenoids. Examples include the sipholanes, sodwanones and other triterpenoids as well as antheliolide and the T. toxius phenylhexaprenoide metabolites of mixed biogenetic origin.     

Epizootic equine influenza in Tunisia

The authors describe an equine influenza epizootic that occurred in Tunisia during February and March 1998 in the regions of Tozeur, Sousse and Tunis. They relate the symptoms, the different stages of diagnosis and the serological results.     

Synthesis of novel pyrroles and fused pyrroles as antifungal and antibacterial agents

Pyrroles and its fused forms possess antimicrobial activities, they can easily interact with biomolecules of living systems. A series of substituted pyrroles, and its fused pyrimidines and triazines forms have been synthesised, all newly synthesised compound structures were confirmed by spectroscopic analysis. Generally, the compounds inhibited growth of some important human pathogens, the best effect was given by: 2a, 3c, 4d on Gram-positive bacteria and was higher on yeast (C. albicans), by 5c on Gram-negative bacteria and by 5a then 3c on filamentous fungi (A. fumigatus and F. oxysporum). Such results present good antibacterial and antifungal potential candidates to help overcome the global problem of antibiotic resistance and opportunistic infections outbreak. Compound 3c gave the best anti-phytopathogenic effect at a 50-fold lower concentration than Kocide 2000, introducing a safe commercial candidate for agricultural use. The effect of the compounds on DNA was monitored to detect the mode of action.