Mutual entrainment of two pacemaker cells. A study with an electronic parallel conductance model

Repetitive firing of pacemaker cells was simulated with the use of an electronic Hodgkin-Huxley-like membrane model having a capacitance, a sodium-, a potassium- and a leakage conductance connected in parallel. The frequency of firing of the model cells was controlled by the leakage conductance. Two such model cells of sometimes widely different intrinsic frequencies were coupled through a coupling resistance R_c. Mutual synchronization was allowed to occur by decreasing R_c in small steps from high to low values.The lower R_c, the more the ratio of the mean frequencies of both cells approaches unity. Around certain R_c values stable entrainment occurs during which the mean frequencies are related as simple integral values m: n (e.g. 2:1, 3:2, 4:3, 1:1 for decreasing R_c). Within the range of a fixed m: n entrainment the phase difference between the oscillations of the two cells declines with R_c. When R_c is close to the range ofm: n entrainment, “almost entrainment” occurs in which m: n entrainment is periodic. But also further away from the range of m: n entrainment periodic variations in action potential interval occur.The model cells were adjusted in such a way that a depolarizing current pulse can only advance the first occurring and all subsequent action potentials. This property is used to explain effects of R_c on the mean frequency of the two cells both within and without the R_c ranges of entrainment. Furthermore, it is illustrated how in certain cases the synchronized frequency at R_c = 0 ω follows from simple electrical considerations of the properties of the uncoupled cells.Several of the entrainment phenomena observed are well known in the fields of electronic relaxation oscillators, clinical electrocardiography and circadian rhythms, though with different terminologies. The present model results exemplify the general nature of these phenomena and clarify entrainment phenomena, recently observed in coupling experiments with pacemaker cells from embryonic heart tissue.     

黄地老虎核型多角体病毒的一些特性

黄地老虎核型多角体病毒(Agrotis segetum Nulear Polyhedrosis Virus简称AsNPV)的国内分离株(AsNPV^C),多角体呈六边形,大小1.7—2.6μm,为多粒包埋类型.每个病毒束内有2—7个核衣壳,大小约52nm×308nm.感染烟青虫(Heliothis assttlta)后分离到的多角体(As-HaNPV)其形状不规则,大小0.7—2.6μm,亦为多粒包埋类型.核衣壳2—6个不等,大小约40nm×300nm.EcoR1和HindⅢ限制性内切酶电泳图谱分析表明,AsNPV^CDNA和As-HaNPV DNA的EcoRI、HindIII酶切图谱一致,两者与HaNPV DNA的EcoRI,HindⅢ酶切图谱存在明显差异,AsNPV^C DNA的EcoRI酶切图谱共有15个片段,分子量在12.74×10⁶—1.18×10⁶道尔顿之间,总分子量约88.6×10⁶道尔顿,相当于134.25kbp.HaNPV DNA的EcoRI酶切图谱共有19个片段,分子量在13.89×10⁶—1.10×10⁶道尔顿之间,总分子量约93.86×10⁶道尔顿,相当于142.25kbp.AsNPV对黄地老虎2龄和4龄幼虫以及对烟青虫4龄幼虫的LD_{50分别为:1.4×10⁵pIB、7.4×10⁴PIB和2.61×10⁴PIB.}     

Regulation of Na,K-pump-mediated transport by prolactin in cultured human prostate epithelial cells.

The prostate gland is unique in its ability to secrete large amounts of zinc and citrate, suggesting that it employs unusual transport mechanisms. Intracellular ionic homeostasis in prostate is likely to be mediated by the Na,K-pump, yet there have been few studies of its regulation in this tissue. Accordingly, we explored the expression of the Na,K-pump in PC3 cells, an established cell line of human prostate epithelial cells. Total RNA from confluent monolayers of PC3 cells was isolated, reverse transcribed, and the resulting complementary DNA was amplified by polymerase chain reaction using primers specific for each of the pump's constituent subunits. The amplification revealed a complex pattern of Na,K-pump expression, with detection of mRNAs encoding the alpha1-, alpha3-, alpha4-, betal-, beta2- and beta3-isoforms. We next examined the effect on pump activity of prolactin, an important mediator of cell proliferation in prostate cancer. Monolayers exposed to 10 nM prolactin for 24 hr revealed an inhibition of 40% in ouabain-sensitive 86Rb+ uptake, a sensitive measure of pump-mediated transport. These experiments suggest that the unique transport properties of prostate may depend, at least in part, on a complicated pattern of Na,K-pump expression and regulation.     

Tubuloside A,a phenylethanoid glycoside,alleviates diclofenac induced hepato-nephro oxidative injury via Nrf2/HO-1

The most prominent adverse effects of nonsteroidal anti-inflammatory drugs (NSAIDs) such as diclofenac (DF) are hepato-renal damage. Natural antioxidants can be preferred as an alternative and/or combination to improve this damage. This present study was conducted to evaluate the protective effect of Tubuloside A (TA) against diclofenac (DF)-induced hepato-renal damage. TA (1 mg/kg, ip) was administered to male Sprague–Dawley rats for 5 days, and DF (50 mg/kg, ip) was administered on Days 4 and 5. Plasma aspartate amino transferase, alanine amino transferase, alkaline phosphatase, blood urea nitrogen and creatinine were measured to evaluate liver and kidney functions. Additionally, oxidative stress parameters (malondialdehyde, glutathione, superoxide dismutase, catalase, and 8-oxo-7,8-dihydro-2′-deoxyguanosine) in blood, liver, and kidney tissues, changes in mRNA expression of genes involved in the Nrf2/HO-1 signalling pathway (Nrf2, HO-1, NQO-1, IL-6, iNOS, Cox-2, TNF-α, IL1-β and NFκB) and apoptotic process (Bcl-2, Cas-3 and Bax) in liver and kidney tissues were determined. Additionally, tissue sections were evaluated histopathologically. Biochemical, histopathological, and molecular results demonstrated the hepato-renal toxic effects of DF, and TA treatment protected the liver and kidney from DF-induced damage. This provides an explanation for the hepato-nephro damage caused by DF and offers new ideas and drug targets together with TA for the prevention and treatment of DF injury.     

Effects of waterfowl, large fish and periphyton on the spring growth of Potamogeton pectinatus L. in Lake Mogan, Turkey

It has been argued that waterfowl and fish may threaten growth of submerged macrophytes, especially in spring during the early growth phase when plant biomass is low. A small reduction of biomass at that time might delay growth or decrease subsequent productivity. We investigated the impact of waterfowl and large fish on the spring growth of fennel pondweed (Potamogeton pectinatusL.) by employing an exclosure experiment in the macrophyte-dominated clear-water Lake Mogan, Turkey. Birds and large fish were excluded from eight plots and both in situvegetation and macrophytes kept in pots were compared to eight open plots. Also, to investigate the effect of periphyton on plant growth it was removed from half of the pot plants. Exclusion of waterfowl and fish may decrease predation on macroinvertebrates, which in turn may affect periphyton, and macrophyte growth, why macroinvertebrates also were sampled. Waterfowl density was high (15–70 ind. of coot, Fulica atraL. ha^–1), abundance of submerged plants was also high with a surface coverage of 70–80%, and benthivorous fish were present, mainly tench, (Tinca tincaL.) and carp, (Cyprinus carpioL.). Exclusion of waterfowl and large fish did not significantly affect the spring growth of pondweed; neither plants growing in situnor kept in pots. Removal of periphyton from the plants in the pots did not favour growth. The density of macroinvertebrates was not affected by the exclusion of waterfowl and large fish, but it was positively related to aboveground biomass of fennel pondweed. We suggest that even if waterfowl and large fish are in high densities, their effect on fennel pondweed spring growth in lakes with abundant submerged vegetation, such as Lake Mogan, is low.     

Systemic endocrine instigation of indolent tumor growth requires osteopontin

The effects of primary tumors on the host systemic environment and resulting contributions of the host to tumor growth are poorly understood. Here, we find that human breast carcinomas instigate the growth of otherwise-indolent tumor cells, micrometastases, and human tumor surgical specimens located at distant anatomical sites. This systemic instigation is accompanied by incorporation of bone-marrow cells (BMCs) into the stroma of the distant, once-indolent tumors. We find that BMCs of hosts bearing instigating tumors are functionally activated prior to their mobilization; hence, when coinjected with indolent cells, these activated BMCs mimic the systemic effects imparted by instigating tumors. Secretion of osteopontin by instigating tumors is necessary for BMC activation and the subsequent outgrowth of the distant otherwise-indolent tumors. These results reveal that outgrowth of indolent tumors can be governed on a systemic level by endocrine factors released by certain instigating tumors, and hold important experimental and therapeutic implications.     

Evolution of the HIV-1 env Gene in the Rag2?/? γC?/? Humanized Mouse Model

Rag2^−/− γ_C^−/− mice transplanted with human hematopoietic stem cells (DKO-hu-HSC mice) mimic aspects of human infection with human immunodeficiency virus type 1 (HIV-1), including sustained viral replication and CD4⁺ T-cell decline. However, the extent of HIV-1 evolution during long-term infection in these humanized mice, a key feature of the natural infection, has not been assessed fully. In this study, we examined the types of genotypic and phenotypic changes in the viral env gene that occur in the viral populations of DKO-hu-HSC mice infected with the CCR5-tropic isolate HIV-1_JRCSF for up to 44 weeks. The mean rate of divergence of viral populations in mice was similar to that observed in a cohort of humans during a similar period of infection. Many amino acid substitutions were common across mice, including losses of N-linked glycosylation sites and substitutions in the CD4 binding site and in CD4-induced epitopes, indicating common selective pressures between mice. In addition, env variants evolved sensitivity to antibodies directed at V3, suggesting a more open conformation for Env. This phenotypic change was associated with increased CD4 binding efficiency and was attributed to specific amino acid substitutions. In one mouse, env variants emerged that exhibited a CXCR4-tropic phenotype. These sequences were compartmentalized in the mesenteric lymph node. In summary, viral populations in these mice exhibited dynamic behavior that included sequence evolution, compartmentalization, and the appearance of distinct phenotypic changes. Thus, humanized mice offer a useful model for studying evolutionary processes of HIV-1 in a complex host environment.Animal models of HIV-1 infection are important tools for studying transmission, replication, and pathogenesis, as well as therapeutic intervention, of HIV-1 infection. Nonhuman primates such as rhesus macaques, infected with simian or chimeric simian/human immunodeficiency viruses (SIV or SHIV, respectively), represent well-characterized and highly relevant models; however, key limitations include expense, genetic variability of the host animals, and the fact that SIV, while closely related, is distinct from HIV-1. Therefore, small animal models that support HIV-1 infection and recapitulate many aspects of the human infection have been sought using several approaches.Recent approaches have involved the use of genetically immunodeficient mice that have been reconstituted using human-derived hematopoietic stem cells (HSC) (known as humanized mice). Several models have been developed based on this approach, including Rag2^−/− γ_C^−/− (DKO) and NOD/SCID/γ_C^−/− (NOG or NSG) mice transplanted with human HSC (DKO-hu-HSC or NOG-hu-HSC mice) (40, 92) and the NOD/SCID mouse with transplanted human fetal thymus and liver tissue in addition to HSC (62). These models all support HIV-1 infection (1, 3, 6, 30, 87, 96, 102; for a review of these models, see the work of Denton and Garcia [22]). The DKO-hu-HSC mouse lacks both recombination activating gene 2 (Rag2) and the cytokine receptor common gamma chain (γ_C), and as a result, it does not generate murine T, B, and natural killer (NK) cells but supports engraftment of HSC and differentiation of human myeloid and lymphoid lineages. Immune reconstitution in this model likely involves education of human T cells in the mouse thymus and dissemination of differentiated human lymphoid subsets into the peripheral blood and to multiple lymphoid tissues, including lymph nodes, spleen, and bone marrow (92). The DKO-hu-HSC mouse, along with the other humanized mouse models, has been used in studies of transmission (5, 21), pathogenesis (43), and viral inhibition (16, 21, 53, 88, 94).One important feature of HIV-1 infection is the diversification and evolution of the viral genome over the course of infection. Diversification occurs most prominently in the envelope (env) gene, which encodes the viral surface glycoprotein (Env). Env mediates viral entry into cells through attachment to the primary receptor CD4, which primes Env for engagement with a coreceptor, either CCR5 or CXCR4, triggering virion fusion with the cellular plasma membrane (54). HIV-1 infection is typically established by one or a few CCR5-tropic (R5) variants that give rise to an initially homogenous viral population, which then diversifies over the course of chronic infection (45, 84). Diversification of Env results from immune selective pressures (27), isolation in or adaptation to different cellular and anatomical compartments (20, 28, 33, 46, 51), and selection for altered CD4 affinity (72, 90, 95) and coreceptor tropism (26, 39). In many cases, during late-stage infection, variants emerge from the R5 virus population that are CXCR4 tropic (X4), an event that is often associated with accelerated CD4 T-cell loss and progression to AIDS (9, 18, 89). In an effort to determine if any of these aspects of HIV-1 evolution are exhibited in the humanized mouse model, we examined the extent of HIV-1 diversification and the types of evolutionary changes that occur in env in mice infected with CCR5-tropic HIV-1 for up to 44 weeks.Sampling of viral env variants from the peripheral blood plasma over the course of the infection revealed increasing diversity and divergence of the viral population at rates similar to those observed in natural infection. Mutations were identified that affected Env conformation and sensitivity to neutralizing antibodies, CXCR4 coreceptor use, and potential N-linked glycosylation sites. Other mutations potentially affecting the Env phenotype were identified in CD4 binding sites and CD4-induced epitopes. The patterns of substitutions indicated that certain sites were under selection, particularly in cases where the same substitution was identified in multiple mice.This study demonstrates the potential for studying HIV-1 evolution in the DKO-hu-HSC mouse model and also gives insight into the types of selective pressures driving HIV-1 env evolution in this host environment. These findings, while highlighting some of the limitations of this model, will help to inform its appropriate use for studying different aspects of HIV-1 infection, such as the evolutionary constraints placed on HIV-1 during natural infection and in the face of pharmacological and immunological inhibition.