Conservation of DNA sequence in the predicted major late promoter regions of selected mastadenoviruses

The major late promoter (MLP) of the subgroup C human adenoviruses is a preeminent model for the study of the mechanisms of basal and activated transcription, both in vivo and in vitro. However, while the structure and function of the human virus MLP has been the subject of extensive investigation, the conservation of the various promoter elements among the adenoviruses from different species has not been examined. Conservation of specific elements would strongly suggest the importance and universality of their function. To address this issue, sequences were obtained from cloned DNAs of several representative Mastadenoviridae, mouse adenovirus type 1 (MAV-1), Tupaia adenovirus type 1 (TAV-1), and two bovine adenoviruses of two distinct subgroups, BAV-3 and BAV-7. The results of the sequencing studies showed that the TATA box and an upstream inverted CAAT box are conserved in all species and that the binding site for transcription factor USF is present in all except MAV-1, in which a sequence similar to an Sp1-binding site is present at a similar position. The initiator element (INR) sequence is not well conserved, and only one or other of the two downstream activating elements, DE1 and DE2, is predicted to be present in the nonprimate virus MLP regions. Ribonuclease protection assays on RNA isolated from MAV-1-infected cells late in infection indicated that the predicted MLP is functional, and transcription initiation and splice donor sites were identified. The human virus MLP is embedded in the essential DNA polymerase sequence on the opposite DNA strand. The primary amino acid sequences of the C-terminal regions of the predicted DNA polymerases show strong conservation of sequence motifs observed in replicative polymerases ranging from prokaryotes to mammals, and additional regions of strong conservation among the adenovirus polymerases. Pairwise comparisons between the newly sequenced regions of the polymerases and previously published sequences show that BAV-7 is most dissimilar to all others, while TAV-1 has a greater similarity to the primate sequences than to the others. The sequence data from both strands were also used to construct phylogenetic trees, based on BAV-7 as the outgroup. The trees constructed from the two sets of sequences are broadly similar, showing close relationships between primate viruses, but differing in the order of divergence of TAV-1 and MAV-1 branches.

Passive immune globulin therapy in the SIV/macaque model: early intervention can alter disease profile

One of the major questions in AIDS is the role that the host immune system and the virus play in the dynamics of infection and the development of AIDS in an infected individual. In order to test the role of antibody in controlling viral infection, high-dose SIV-immune globulin was passively transferred to infected macaques early in infection. Immune globulin purified from the plasma of an SIV-infected long-term non-progressor macaque (SIVIG) or a pool of normal immune globulin (normal Ig) was infused into SIVsmE660-infected macaques (170 mg/kg) at one and fourteen days post infection. Animals were monitored for SIV-specific antibodies, viremia, plasma antigenemia, and clinical course. All animals were infected by SIV. At 16 months post infection, five macaques in the combined control groups have been euthanized, one as a rapid progressor with debilitating disease at 20 weeks post infection. Four macaques from the comparison groups have signs of AIDS, accompanied by high and increasing levels of virus and p27 antigenemia. One of the ten control animals had a very low virus load in plasma and peripheral blood and lymph node mononuclear cells at all times tested and has remained disease-free. In the SIVIG treatment group, two macaques were euthanized at 18-20 weeks due to AIDS, rapid progressors to disease. Three macaques in the SIVIG group had an initial high level of virus in plasma, peripheral blood mononuclear cells (PBMC), and lymph node mononuclear cells (LNMC), which dropped to baseline at 6 weeks post infection and has remained very low or negative for 16 months, a disease profile which has not been observed in untreated animals in this model to date. These macaques have remained clinically healthy. The sixth treated animal is also healthy, with very low virus burden that is detectable only by nested set polymerase chain reaction (PCR). All SIVIG-treated macaques had no detectable p27 plasma antigenemia for the first 10 weeks of infection, demonstrating that the IgG effectively complexed with the virus. The immunological correlates in the treated animals include development of de novo virus-specific antibodies and/or cytotoxic T cell (CTL), both of which are hallmarks of long term non-progressors. The two SIVIG-treated macaques that progress to disease rapidly had no detectable de novo humoral immune responses, as is often seen in rapid HIV disease in humans. Envelope-specific and virus neutralizing antibodies alone were not sufficient to prevent disease progression, as the plasma of both non-progressors as well as progressors had high titers of envelope-specific and neutralizing antibodies against SIVsmE660. Poor clinical prognosis was associated with moderate to high and increasing virus loads in plasma, PBMC, and lymph nodes. Good clinical prognosis correlated with low or undetectable post acute viremia in the peripheral blood and lymph nodes. We hypothesize that SIVIG reduced the spread of virus by eliminating or reducing plasma virus through immune complexes during the first four to 8 weeks of infection and then maintaining this low level of viremia until the host immune response was capable of virus control. Reduction of virus burden early in infection by passive IgG can alter disease outcome in SIV infection of macaques. Modifications of this strategy may lead to effective early treatment of HIV-1 infection in humans.

Recombinant subunit vaccines as an approach to study correlates of protection against primate lentivirus infection

Using pathogenic simian immunodeficiency virus (SIV) infection of macaques as a model, we explored the limits of the protective immunity elicited by recombinant subunit vaccines and examined factors that affect their efficacy. Envelope gp 160 vaccines, when used in a live recombinant virus-priming and subunit-protein-boosting regimen, protected macaques against a low-dose, intravenous infection by a cloned homologous virus SIVmne E11S. The same regimen was also effective against intrarectal challenge by the same virus and against intravenous challenge by E11S grown on primary macaque peripheral blood mononuclear cells (PBMC). However, only limited protection was observed against uncloned SIVmne. Priming with live recombinant virus was more effective than immunization with subunit gp 160 alone, indicating a potential advantage of native antigen presentation and the possible role of cell-mediated immunity in protection. Whole gp 160 was more effective than the surface antigen (gp 130), even though both antigens elicited similar levels of neutralizing antibodies. Animals immunized with the core (gag-pol) antigens failed to generate any neutralizing antibody and were all infected following challenge. However, their proviral load was 10-100-fold lower than that of the control animals, indicating that immune mechanisms such as cytotoxic T lymphocytes (CTL) may play a role. Finally, animals immunized with both the core and the envelope antigens generated significant protective immunity, even with relatively low neutralizing antibodies. Taken together, these results indicate that multiple mechanisms may contribute to protection. It may therefore be advantageous to incorporate multiple antigens in the design of recombinant subunit vaccines against acquired immunodeficiency syndrome (AIDS).

Development of a chronically catheterized maternal-fetal macaque model to study in utero mother-to-fetus HIV transmission: a preliminary report

The lack of a representative animal model that permits frequent in utero fetal blood sampling is a major limiting factor for the study of maternal-fetal HIV transmission. Therefore, we have developed a maternal-fetal virus infection model using chronically catheterized macaques to simultaneously study the time-course of viral infection in the mother and the response of the fetus to maternal HIV infection. Pregnant macaques were infected with 10(3) infectious units of HIV-2(287); every 3 days blood samples from both the mother and the fetus as well as amniotic fluid samples were collected. We found a varying degree of peak and time-to-peak virus load, virus-infected PBMCs, and free virus (determined by QC-RNA-PCR method) in maternal blood. Two of the three mothers with more than 10(8) copies of viral RNA/ml of plasma at peak viremia transmitted the virus to their fetuses at about 14 days post-infection. As observed with HIV-2(287) infected mothers, virus-infected fetuses also produced a rapid rate of CD4+ cell decline in utero.

[The relationship between integrated fish farming and human influenza pandemic]

The study was carried out for reviewing the hypothesis on the relationship between integrated fish farming (IFF) and human influenza A pandemic using study methods of longitudinal epidemiology, ecology and serology. Four rural villages with IFF, non-IFF and non-fish farming, selected from two provinces (Henan and Shandong of PRC) were investigated for the status about human influenza A epidemic and infections with human, duck, swine influenaz A viruses in those communities. The results put forward views on that there is no relation between IFF and the increase of incidence rate, infection rate and antibodies level to human influenza A virus. Duck may play an important role in the increase of infection rate to human influenza A viruses among human communities. Pigs seem not to play obvious role in the increase of infection rate to human influenza A viruses among human communities. Human, duck, swine influenza A viruses may spread among human duck and pigs communities interchangably.

Studies of complement-activating antibodies in the SIV/macaque model of acute primary infection and vaccine protection

Questions regarding the potential impact of complement-activating antibodies on lentivirus pathogenesis and vaccine development were addressed in the SIV/macaque model by evaluating sera for activity related to complement-mediated, antibody-dependent enhancement (C'-ADE) of SIV infection in vitro. C'-ADE activity in sera obtained during acute primary infection in macaques inoculated with SIVmac251 appeared before neutralizing antibodies and coincided with the initial peak and decline of plasma antigenemia. The power of C'-ADE activity (i.e., virus production measured by p24 immunoassay) decreased as titers of neutralizing antibodies increased in these animals, suggesting a balance in the net effect between C'-ADE and neutralizing activities in vitro. Antibodies with C'-ADE activity were also induced in macaques immunized with live-attenuated SIVmac239/nef-deletion or primed with recombinant SIVmne gp120 vaccinia virus and boosted with SIVmne rgp160. The titer (i.e., last serum dilution to show enhancement), peak (i.e., serum dilution producing the greatest enhancement as measured by p24 production), and power (i.e., magnitude of p24 production at the peak titer) of C'-ADE activity in sera obtained from vaccinated macaques on the day of challenge were comparable to those of sera from infected macaques and showed no correlation with vaccine outcome, where some protected animals had C'-ADE profiles that resembled those of unprotected animals. The results of these studies suggest that antibodies having C'-ADE activity in vitro could contribute to virus replication or, alternatively, to virus clearance during the acute stage of SIV infection in macaques.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of three N-linked glycans in the V4-V5 region of HIV-1 gp 120, dispensable for CD4-binding and fusion activity of gp 120

Site-directed mutagenesis was used to study the biological significance of three N-linked glycans (linked to Asn406, Asn448, and Asn463), situated in the CD4-binding region of gp120. Mutagenesis was carried out in a phage M13 system, and the mutated env genes were inserted into recombinant vaccinia virus (r-vaccinia virus). To evaluate if the level of expression affected the biological phenotype of mutant gp120, we expressed the envelope glycoproteins using either a weak (7.5 K) or a strong (11 K) promoter of vaccinia virus. The expression of mutated env proteins was analyzed after infecting CD4-expressing HeLa cells with the r-vaccinia virus, by monitoring the ability of the infected cells to generate CD4-dependent syncytia. Env gene products lacking all three glycans as well as env gene products lacking different permutations of one or two glycans were analyzed. All mutated gp120 species had the expected electrophoretical mobility as anticipated from elimination of one, two, and three N-linked glycans, respectively. Moreover, all mutant env gene products demonstrated the same capacity to induce formation of syncytia, irrespective of using the weak or strong promoter for expression. These data indicate that the three N-linked glycans studied are dispensable for HIV env gene products to function in CD4-binding and the subsequent fusion step.

Effect of MTP-PE liposomes and interleukin-7 on induction of antibody and cell-mediated immune responses to a recombinant HIV-envelope protein

We investigated the ability of human recombinant interleukin-7 (IL-7) to enhance the immune responses of mice vaccinated with either the alum-associated or liposome-formulated recombinant human immunodeficiency virus (HIV)-envelope protein, env-2-3SF2 (a nonglycosylated denatured gp 120 of HIV-1SF2 produced in genetically engineered yeast). Pathogen-free (C3H) mice were vaccinated on days 0, 14, and 28 with 10 micrograms of either the alum-associated env-2-3SF2 or liposome-formulated env-2-3SF2, both containing a lipophylic muramyl tripeptide, MTP-PE. Liposome-formulated IL-7 (5 micrograms/mouse) or empty liposomes were given on days 7, 14, 21, and 28. Antibody response against the immunized antigen, evaluated on day 21 and day 35 or 42, showed that liposome-formulated antigen induced higher antibody titer than did alum-associated antigen, and these antibody responses can be enhanced by concurrent administration of IL-7 liposomes. Spleen cells were harvested on day 21 and day 35 or 42 to evaluate cytotoxic T lymphocyte responses directed against autologous cells infected with vaccinia virus-expressing HIV-envelope protein. Mice treated with liposome-formulated antigen expressed the highest cytotoxic t-lymphocyte (CTL) activity, regardless of whether IL-7 liposome was given as an immune potentiator. In contrast, spleen cells from mice vaccinated with alum-associated antigen exhibited minimal CTL response, which was enhanced by concurrent IL-7 liposome treatment. Collectively, IL-7 liposome treatment enhanced the antibody production of the alum-associated or liposome-formulated env-2-3SF2, whereas its enhancement of CTL activity was detected only in mice vaccinated with alum-associated antigen.

Analysis of cytotoxic T lymphocyte responses to SIV proteins in SIV-infected macaques using antigen-specific stimulation with recombinant vaccinia and fowl poxviruses

Methods to analyze CD8+ CTL responses to simian immunodeficiency virus (SIV)-encoded proteins are essential to understand lentivirus immunopathogenesis and protective immune responses. Recombinant infectious shuttle vectors are useful for analyzing CTL responses to many viruses, including HIV. Therefore, CTL responses in SIV-infected Macaca fascicularis to SIV env and SIV gag/pol were evaluated using specific antigen stimulation with recombinant vaccinia (rVV) and fowl poxviruses (rFPV) containing SIV genes. Peripheral blood mononuclear cells from SIV-infected animals were stimulated with autologous cells infected with rVV expressing SIV env/gag/pol, and CTLs specific for SIV env and for SIV gag/pol were detected by testing for lytic activity in target cells expressing these genes separately. Lymphocyte subset purifications from the effector population demonstrated that the CTL response was mediated by CD8+ cells, and the use of brefeldin A to selectively block antigen presentation in association with MHC class I products affirmed this cytolytic activity was class I restricted. The use of rVV to analyze responses to SIV genes is potentially problematic in hosts immunized to vaccinia. Fowl poxvirus is an alternative virus that has many of the molecular advantages of vaccinia virus but is genomically distinct. Therefore, the ability of rFPV to expand and detect SIV-specific CTLs was evaluated. Although there was no cytopathic effect following infection with rFPV, macaque cells infected with this vector did express rFPV gene products, and could be used as stimulator and target cells to detect SIV-specific CD8+ CTLs. The results suggest that these recombinant viral vectors can be used to specifically stimulate CD8+, MHC class I-restricted CTLs reactive to SIV proteins, and should facilitate evaluating CTL responses in both SIV-infected animals and animals vaccinated against SIV.

Effect of nonprotective vaccination on antibody response to subsequent human immunodeficiency virus infection

We have investigated the systemic anti-HIV antibody response in chimpanzees who were immunized with live vaccinia containing either the HIV envelope glycoprotein (gp160IIIB) or a control antigen (herpes simplex virus glycoprotein D) and then challenged with either a high dose (300,000 TCID50) or low dose (100 TCID50) of HIVIIIB. HIV was subsequently isolated from all animals, indicating failure of the vaccination to protect against HIV infection. Serum antibody responses were evaluated before immunization, at the time of challenge with HIV, and at multiple time points in the 9 mo after challenge. Immunization resulted in a more rapid rise of antibody to gp160 in both high and low dose animals. Antibodies to the V3 loop induced upon infection were unaffected by immunization. In low dose animals, neutralizing antibody rose more rapidly and to higher levels in the immunized animals as compared with the control. There was no difference in neutralizing antibodies between immunized and control chimpanzees in the high dose group. Epitope mapping of the anti-gp 160 response indicated that immunization with gp160 vaccinia induced a postinfection antibody response to a region of gp41 (amino acids 718-743) that was not immunogenic in control-vaccinated animals. These data indicate that failed vaccination with the HIV envelope can alter both the timing and epitope specificity of the subsequent anti-HIV antibody response. These studies also define the evolution and fine specificity of the antibody response during the critical period immediately postinfection.

[A comment on two medicinal aroids huzhang and tiannanxing]

An original error on Huzhang and Tiannanxing in Li Shizhen's "Bencao Gangmu" (Compendium of Materia Medica, 1596) is corrected in this paper. The conclusion is that Huzhang in "Shen Nong's Materia" (around 200) should be the tuber of Pinellia pedatisecta and Tiannanxing in "Kaibao Bencao" (974) the tuber of Arisaema heterophyllum but they were merged or confused by Li Shizhen. The former, in fact, has been cultivated, marketed, exported and used medically for its high quality, but it has disappeared from herbal literatures owing to Li's error. Therefore, the above-mentioned correction should be accepted in the next edition of Pharmacopoea of the people's Republic of China.

Enhanced immunity to human immunodeficiency virus (HIV) envelope elicited by a combined vaccine regimen consisting of priming with a vaccinia recombinant expressing HIV envelope and boosting with gp160 protein

Transmission studies have suggested that an optimal human immunodeficiency virus type 1 (HIV-1) vaccine should induce both neutralizing antibodies and cytolytic T cells to eliminate free virus and infected cells. A phase I trial in healthy HIV-1-seronegative persons was conducted with a combination HIV-1 vaccine regimen (strain IIIB) consisting of priming with a recombinant vaccinia (vac/env) virus expressing HIV-1 envelope and boosting with a gp160 glycoprotein derived from a recombinant baculovirus (rgp160). T-cell and antibody responses detected after immunization with either vac/env alone or rgp160 alone were generally of low magnitude and transient, and no subject developed neutralizing antibodies. In contrast, recipients of the combination regimen demonstrated in vitro T-cell proliferative responses to homologous HIV-1 antigens that were 3- to 10-fold higher than responses with either vaccine alone, and these responses were sustained for > 18 months in 75% of recipients. Moreover, both CD8+ and CD4+ cytolytic T cells were detected. Antibody responses (titer, 1:800 to 1:102,400) to homologous HIV envelope developed in all recipients of the combination regimen, and neutralizing antibodies were detected in 7 of 13. Thus, immunization with a live virus vaccine followed by boosting with a soluble protein offers promise for inducing the broad immunity needed in an HIV vaccine.

Terpestacin, a new syncytium formation inhibitor from Arthrinium sp

Terpestacin, a new antibiotic which inhibits syncytium formation, was isolated from Arthrinium sp. FA1744 (ATCC 74132). The structure of terpestacin was elucidated as a bicyclic sesterterpene on the basis of spectroscopic data and chemical derivatization.

Protection of vaccinia-primed macaques against SIVmne infection by combination immunization with recombinant vaccinia virus and SIVmne gp160

Two Macaca fascicularis with preexisting immunity to vaccinia virus were immunized twice with recombinant vaccinia virus expressing SIVmne gp160. Their SIV-specific antibody responses were lower than that of vaccinia-naive animals immunized similarly. Upon repeated boosting with gp160, the SIV-specific antibody titers in vaccinia-primed animals reached similar levels as vaccinia-naive animals and with comparable neutralizing titers. Both animals were protected against repeated intravenous challenge with low-dose SIVmne E11S. These results are significant because SIVmne E11S infection in M. fascicularis is pathogenic and leads to AIDS-like diseases.

Long-term protection of macaques against high-dose type D retrovirus challenge after immunization with recombinant vaccinia virus expressing envelope glycoproteins

Recombinant vaccinia virus expressing the envelope proteins of type D retrovirus-Washington (SRV-2/W) was used to immunize macaques against SRV-2 infection. Four immunized macaques which had resisted a prior low-dose challenge were rechallenged with a high dose (10(6) infectious particles) of SRV-2 two years after being immunized. All four non-immunized control macaques became infected, but the four vaccinated animals resisted this intravenous challenge, as determined by the inability to detect SRV-2 in peripheral blood mononuclear cells and by the lack of seroconversion to new viral antigens.

Carbohydrate determinant NeuAc-Gal beta (1-4) of N-linked glycans modulates the antigenic activity of human immunodeficiency virus type 1 glycoprotein gp120

In the present study we investigated to what extent the peripheral carbohydrate structure of N-linked glycans influences the antigenic properties of human immunodeficiency virus type 1 glycoprotein 120 (gp120). Recombinant gp120 was purified from GMK cells infected with a recombinant vaccinia virus expressing gp120. Purified gp120 was then coated onto 96-well ELISA microplates and subjected to sequential removal of peripheral monosaccharide units. Modified or unmodified gp120 was then incubated with monoclonal antibodies recognizing specific epitopes of gp120 and with a reporter lectin to determine the extent of carbohydrate elimination. Antibody and lectin binding was quantified in an enzyme-linked system. We found that the carbohydrate structure NeuAc-Gal beta (1-4) of N-linked glycans, defined both by lectin reactivity and by specific glycosidases, is involved in modulating the binding of antibody to a number of epitopes of peptide nature. The binding of antibody to one class of epitopes, situated in a region between amino acids 200 and 230, was strongly increased by removal of NeuAc-Gal beta (1-4), whereas the binding to epitopes in the V3 region was decreased and the binding to epitopes in the far N-terminal region was not altered by the treatment. These results suggested that peripheral structures of N-glycans are involved in modulating the overall conformation of gp120.

Inhibition of virus production in peripheral blood mononuclear cells from human immunodeficiency virus (HIV) type 1-seropositive donors by treatment with recombinant HIV-like particles

We have previously reported on the assembly of recombinant human immunodeficiency virus (HIV)-like particles that contain gag structural proteins and present env glycoproteins gp120 and gp41 on their surfaces (O. Haffar,. J. Garriques, B. Travis, P. Moran, J. Zarling, and S.-L. Hu, J. Virol. 64:2653-2659, 1990). On the basis of their structures, we hypothesized that the recombinant particles would interfere with virus infection and tested our hypothesis in vitro by using peripheral blood mononuclear cells (PBMC) from HIV type 1-seropositive donors. Addition of the recombinant particles to PBMC concomitant with stimulation by anti-CD3 inhibited virus production, as determined by reduced levels of p24 in the culture supernatants. This inhibition of p24 production correlated with lower levels of cell-associated viral DNA. Several lines of evidence suggested that the recombinant particles exerted their antiviral effects primarily by inhibiting virus production from latently infected cells and not by inhibiting subsequent virus spread. Importantly, CD4+ T-cell stimulation by specific antigen or by anti-CD3 was not inhibited by treatment with the recombinant particles. This apparent selective inhibition of virus replication in infected PBMC represents a novel property of the recombinant HIV-like particles.

Induction of cytotoxic T lymphocytes specific for a syngeneic tumor expressing the E6 oncoprotein of human papillomavirus type 16

Human papillomavirus (HPV) type 16 has been implicated in the etiology of cervical carcinomas, but it is unknown whether HPV-specific immunity can function in controlling the growth of HPV-associated carcinomas. We previously demonstrated that CD8+ T lymphocytes can inhibit the in vivo outgrowth of murine tumor cells transfected with the HPV-16 E7 gene and have now established a murine model to study the CTL responses to the E6 oncoprotein of HPV-16. Immunization of C3H/HeN mice with syngeneic fibroblasts expressing a transfected HPV-16 E6 gene induced regression of transplanted tumors expressing this gene. Populations of CTL isolated from the spleens of mice whose E6+ tumors had regressed were shown to specifically lyse E6+ target cells. The cytolytic activity was mediated by CD8+ CTL in a MHC restricted pattern. These data and our previous findings with transfected tumor cells expressing the E7 gene, support the conclusion that tumor cells associated with HPV-16 can be inhibited by CTL specific for molecules encoded by the HPV-16 E6 and E7 genes.

Induction of cytotoxic T lymphocytes specific for a syngeneic tumor expressing the E6 oncoprotein of human papillomavirus type 16

Human papillomavirus (HPV) type 16 has been implicated in the etiology of cervical carcinomas, but it is unknown whether HPV-specific immunity can function in controlling the growth of HPV-associated carcinomas. We previously demonstrated that CD8+ T lymphocytes can inhibit the in vivo outgrowth of murine tumor cells transfected with the HPV-16 E7 gene and have now established a murine model to study the CTL responses to the E6 oncoprotein of HPV-16. Immunization of C3H/HeN mice with syngeneic fibroblasts expressing a transfected HPV-16 E6 gene induced regression of transplanted tumors expressing this gene. Populations of CTL isolated from the spleens of mice whose E6+ tumors had regressed were shown to specifically lyse E6+ target cells. The cytolytic activity was mediated by CD8+ CTL in a MHC restricted pattern. These data and our previous findings with transfected tumor cells expressing the E7 gene, support the conclusion that tumor cells associated with HPV-16 can be inhibited by CTL specific for molecules encoded by the HPV-16 E6 and E7 genes.

An O-linked carbohydrate neutralization epitope of HIV-1 gp 120 is expressed by HIV-1 env gene recombinant vaccinia virus

Previous studies have disagreed about the presence of O-linked carbohydrate epitopes on gp 120 of HIV, although antibodies against short-chain O-linked glycans neutralize HIV infection and block syncytium formation in vitro. To settle this question, we analysed the O-linked glycans of gp 120 by chemical methods using purified HIV-1 gp 120 from cells infected with recombinant vaccinia virus solely expressing gp 160 or gp 120. Alkaline borohydride degradation of recombinant gp 120 released monosaccharides and also slightly larger structures (di/trisaccharides) by a beta-elimination, confirming the presence of simple O-linked oligosaccharides. The functional activity as neutralisation epitopes of the O-linked oligosaccharides expressed on recombinant gp 120 was preserved, since fusion between uninfected CD4+ cells and cells infected with recombinant vaccinia was blocked by monoclonal antibodies to the O-linked oligosaccharides of gp 120. Although the mechanism for HIV induction of O-linked oligosaccharide neoantigens is unknown, these results indicate that the O-linked neutralization epitopes are inherent to the glycoprotein itself, and that the unusual appearance of simple O-linked oligosaccharides on gp 120 is independent of any interaction between the host cell and retroviral genes other than env.

Sulfhydryl oxidation down-regulates T-cell signaling and inhibits tyrosine phosphorylation of phospholipase C gamma 1

Early events in both T-cell receptor (CD3)- and CD4-induced signal transduction pathways include tyrosine phosphorylation of protein substrates, the generation of phosphatidylinositol-phosphate breakdown products, and the mobilization of intracellular Ca2+. Oxidative stress in T cells mediated by sulfhydryl-reactive nonpolar maleimides was shown previously to down-regulate both receptor-mediated Ca2+ mobilization and interleukin 2 production. Here we show that N-ethylmaleimide suppresses both CD3- and CD4-induced Ca2+ responses in human T cells correlating with a reduction in the level of phospholipase C gamma 1 (PLC gamma 1) tyrosine phosphorylation. The inhibition of tyrosine phosphorylation of PLC gamma 1 and additional protein substrates was observed at concentrations of N-ethylmaleimide above 20 microM, whereas lower concentrations of oxidant appeared to increase tyrosine kinase activity following cell stimulation. Sulfhydryl oxidation did not directly affect the catalytic activity of PLC gamma 1, since immunopurified enzyme from N-ethylmaleimide-treated T cells was fully active. Although N-ethylmaleimide treatment of T cells did not cause a direct effect on total pp56lck kinase activity measured in vitro, the interaction between CD4 and pp56lck was oxidation-sensitive in vivo. However, CD3-induced signaling was inhibited at N-ethylmaleimide concentrations lower than that required for CD4/pp56lck dissociation, suggesting that CD3-associated tyrosine kinase activity involves acutely sensitive regulatory thiols. In addition to chemically induced sulfhydryl oxidation, naturally regulated cellular redox states appear to dictate the potential for T-cell responsiveness, since degranulating human peripheral blood neutrophils inhibited CD3-induced Ca2+ mobilization in T lymphocytes. These data indicate that signal transduction in T cells involves the activation of PLC gamma 1 by tyrosine phosphorylation through an oxidation-sensitive intermediate between surface receptors and tyrosine kinases, perhaps including the interaction between CD4 and pp56lck.

Evaluation of protective efficacy of recombinant subunit vaccines against simian immunodeficiency virus infection of macaques

Simian immunodeficiency virus (SIV) was used as a model to study the protective efficacy of an immunization regimen currently being evaluated as candidate vaccines against HIV in human subjects. Four Macaca fascicularis were first immunized with recombinant vaccinia virus expressing the envelope glycoprotein gp160 of SIVmne and then boosted with subunit gp160. Both cell-mediated and humoral immune responses against SIV, including neutralizing antibodies, were elicited. The macaques were shown to be protected from a homologous virus infection as determined by serology, lymphocyte cocultivation, polymerase chain reactions and in vivo transmission analyses. Four unimmunized control animals were readily infected. However, viremia in infected control animals could decrease substantially following the initial phase of infection so that persistent infection might not be readily detectable.

Protection of macaques against SIV infection by subunit vaccines of SIV envelope glycoprotein gp160

Simian immunodeficiency virus (SIV) is a primate lentivirus related to human immunodeficiency viruses and is an etiologic agent for acquired immunodeficiency syndrome (AIDS)-like diseases in macaques. To date, only inactivated whole virus vaccines have been shown to protect macaques against SIV infection. Protective immunity was elicited by recombinant subunit vaccines. Four Macaca fascicularis were immunized with recombinant vaccinia virus expressing SIVmne gp160 and were boosted with gp160 produced in baculovirus-infected cells. All four animals were protected against an intravenous challenge of the homologous virus at one to nine animal-infectious doses. These results indicate that immunization with viral envelope antigens alone is sufficient to elicit protective immunity against a primate immunodeficiency virus. The combination immunization regimen, similar to one now being evaluated in humans as candidate human immunodeficiency virus (HIV)-1 vaccines, appears to be an effective way to elicit such immune responses.

Recent advances in antitumor vaccines

Immunization with anti-idiotypic antibodies can induce cell-mediated and humoral antitumor immunity in animal models. This immunity can sometimes cause tumor destruction. However, more needs to be learned about how best to induce the type of immune response that is responsible for tumor destruction, since the presence of anti-idiotypic antibodies has been shown occasionally to enhance, rather than to inhibit, tumor growth. There is evidence suggesting that immunization of human cancer patients with Ab2 can have therapeutic benefit, and also that patients who mount a vigorous Ab2 response following treatment with an Ab1 may do clinically better than those who do not make any Ab2. Although the generation of Ab2 related to infused antitumor Ab1 does not cause tumor rejection in the majority of patients, and although the clinical data from patients given Ab2 are scarce, the suggestion that Ab2 may cause destruction of human cancers indicates that further work in this area may become rewarding.

Functional roles of the V3 hypervariable region of HIV-1 gp160 in the processing of gp160 and in the formation of syncytia in CD4+ cells

To study the roles of the V3 hypervariable region (amino acid residues 301-336) of the HIV-1 envelope glycoprotein (gp160) during infection, we constructed recombinant vaccinia viruses that expressed either wild-type gp160 (v-env10) or mutant gp160 in which the V3 region was deleted (v-dl29.1 and v-dl29.2). In v-dl29.1 the V3 loop, formed by disulfide bonding between cysteine residues 301 and 336, was deleted from cys301 to cys336 (inclusive) and replaced by one serine residue. In v-dl29.2 the V3 loop was deleted from arg303 to ala334 and replaced by three residues: gly-ala-gly. Cells infected with all three recombinant vaccinia viruses expressed gp160 on the cell surface, but v-dl29.1-derived gp160 was not cleaved into gp120 and gp41 and did not bind the CD4 glycoprotein. In contrast, gp160 produced by recombinant v-dl29.2 was cleaved normally, and the mutant gp120 produced was secreted and retained binding activity to CD4+ cells. However, both mutants failed to induce syncytia in HeLa CD4+ cells. Thus a disulfide loop at the V3 portion of gp160 is required for cleavage into gp120 and gp41, presumably because the loop is required for proper tertiary structure. The sequence within the V3 loop, however, is not required for cleavage and secretion of gp160, or for binding to CD4+, but this region is essential for gp120-mediated syncytia formation.

An epidemic of hepatitis A attributable to the ingestion of raw clams in Shanghai, China

An epidemic of hepatitis A in 1988 in Shanghai had an overall attack rate of 4083/100,000 population (292,301 cases). The epidemic curve showed three peaks in January and February. A case-control study of 1208 matched pairs supported that clams were the vehicle for the virus (summary odds ratio, 9.47; P less than .001). Analysis of subsets who had eaten clams indicated that only 3.5% with hepatitis A had cooked their clams compared with 18.1% without hepatitis A, and those with the disease consumed more clams. A historical cohort study indicated that approximately 31.7% of the population had eaten clams one or more times between 9 December 1987 and 3 January 1988. The estimated attack rates in those who had and had not eaten clams were 11.93% and 0.52%, respectively (relative risk, 22.94; attributable risk, 11.41%). The three peaks in the consumption curve correlated with those in the epidemic curve. Hepatitis A virus was demonstrated in clams taken from the Shanghai markets and from the catching area.

HIV-specific humoral and cellular immunity in rabbits vaccinated with recombinant human immunodeficiency virus-like gag-env particles

Recombinant human immunodeficiency virus type-1 (HIV-1)-like gag-env particles produced in mammalian cells were inoculated into two New Zealand white rabbits. In parallel, two control rabbits were inoculated with the homologous HIV-1 virions inactivated by ultra violet light (uv) and psoralen treatments. The humoral and cellular immune responses to HIV-1 were evaluated for both groups of animals. Recombinant particles elicited humoral immunity that was specific for all the viral structural proteins. The antibodies recognized both denatured and nondenatured proteins. Moreover, the sera neutralized the in vitro infectivity of the homologous virus in CEM cells. Importantly, the recombinant particles also generated a T helper response by priming with the HIV proteins. Similar results were observed with inactivated virus immunization. Therefore, our results suggest that the recombinant HIV-like particles elicit functional humoral immunity as well as cellular immunity and represent a novel vaccine candidate for AIDS.

Neutralizing antibodies against HIV-1 BRU and SF2 isolates generated in mice immunized with recombinant vaccinia virus expressing HIV-1 (BRU) envelope glycoproteins and boosted with homologous gp160

Anti-human immunodeficiency virus type 1 (Anti-HIV-1) antibody response was compared in four groups of mice following inoculation with HIV-1 gp160, with live recombinant vaccinia virus expressing HIV-1 envelope glycoproteins, or with both immunogens in alternate orders for primary or secondary immunizations. Both subunit and recombinant virus immunogens induced similar levels of antibody response following primary immunization. However, after secondary immunization, mice primed with live recombinant virus and then boosted with subunit gp160 immunogen showed significantly higher antibody response than those in the other three groups. Neutralizing antibodies were generated only in this group of mice and were shown to neutralize both the homologous virus (BRU) and a divergent isolate (SF2) of HIV-1. On the other hand, their reactivities to peptide sequences from the principal neutralizing determinant (PND) of gp120 were limited to the BRU isolate, not SF2 or MN, indicating that the cross-neutralizing activities were directed against determinants other than the linear epitope(s) within the PND. These results also indicate that combined immunization by priming with liver recombinant virus and boosting with subunit immunogen may be more effective than immunization by either immunogen alone.

Effects of mutations in glycosylation sites and disulphide bonds on processing, CD4-binding and fusion activity of human immunodeficiency virus envelope glycoproteins

Site-directed mutagenesis was used to study the biological significance of a disulphide bridge and two N-linked oligosaccharides in the CD4-binding region of the envelope glycoproteins of human immunodeficiency virus type 1. Mutagenesis was performed in a phage M13 system at sites corresponding to the cysteine residue (amino acid 402) and the asparagine residues (390 and 447) of the env gene. The mutated env gene was inserted into a recombinant vaccinia virus under the control of the vaccinia virus 7.5K promoter and the expression of mutated env proteins was analysed by SDS-PAGE, a conventional indirect immunofluorescence assay and by a fluorescence-activated cell sorter. Cysteine 402 was found to be essential for the specific cleavage of gp160 into gp120 and gp41, and for intracellular transport of the protein to the cell surface. CD4-binding and syncytium formation assays demonstrated that the disulphide bridge of cysteine 402 stabilized a conformation essential for receptor binding as well as syncytium formation by CD4+ cells. No altered biological activity compared to that of the wild-type proteins could be detected for the mutant proteins lacking the N-glycosylation sites. These data show that the two conserved glycans attached to asparagine residues 390 and 447 do not play any active role in the formation of the disulphide bridge involving cysteine 402 or in the maintenance of an active conformation of the protein, despite their location within the functionally important CD4-binding region.

Safety of and immunological response to a recombinant vaccinia virus vaccine expressing HIV envelope glycoprotein

In a randomised phase I trial of a recombinant vaccina virus vaccine expressing the gp160 envelope gene of the human immunodeficiency virus (HIVAC-1e) 35 healthy, HIV-seronegative males, 31 of whom had a history of smallpox immunisation and 4 of whom were vaccinia naive, were vaccinated and then boosted 8 weeks later with HIVAC-1e or standard NY strain vaccinia virus. The frequency, duration, and titre of virus isolation from the vaccination site and occurrence of local side-effects were similar between the two groups of vaccinees. Vaccinia-naive (vac-n) subjects shed virus from the vaccination site for longer and at a higher titre than did vaccinia-primed (vac-p) individuals (19 vs 7 days and 10(7) vs 10(5) pfu/ml, respectively). In-vitro T-cell proliferative responses to one or more HIV antigen preparations developed in 13 of 16 vaccinia-primed subjects inoculated with HIVAC-1e. T-cell responses were, however, transient and in no subject did antibodies to HIV become detectable. The 2 vaccinia-naive subjects vaccinated with HIVAC-1e showed strong T-cell responses to homologous and heterologous strains of whole virus and to recombinant gp160 protein that remained detectable for over a year; antibodies to HIV envelope also developed in both. Recombinant vaccinia virus vaccines induce T-cell priming to the foreign gene products in most individuals. If used as the sole immunising agent they will be most efficacious in vaccinia-naive individuals.

Interactions of neosaxitoxin with the sodium channel of the frog skeletal muscle fiber

Neosaxitoxin (neoSTX) differs structurally from saxitoxin (STX) in that the hydrogen on N-1 is replaced by a hydroxyl group. On single frog skeletal muscle fibers in the vaseline-gap voltage clamp, the concentrations for reducing the maximum sodium current by 50% (ED50) at pH's 6.50, 7.25, and 8.25 are, respectively, 4.9, 5.1, and 8.9 nM for STX and 1.6, 2.7, and 17.2 nM for neoSTX. The relative potencies of STX at the different pH's closely parallel the relative abundance of the protonated form of the 7,8,9 guanidinium function, but the relative potencies of neoSTX at the same pH's vary with the relative abundance of the deprotonated N-1 group. In constant-ratio mixtures of the two toxins, the observed ED50's are consistent with the notion that the two toxins compete for the same site. At pH's 6.50 and 7.25, the best agreement between observed and computed values is obtained when the efficacy term (epsilon) for either toxin is 1. At pH 8.25 the best agreement is obtained if the efficacy is 1 for STX but 0.75 for neo-STX. The marked pH dependence of the actions of neoSTX probably reflects the presence of a site in the receptor that interacts with the N-1 -OH, in addition to those interacting with the 7,8,9 guanidinium and the C-12 hydroxyl groups. Considering the three-dimensional structure of the STX and neoSTX molecules, the various site points are probably located in a fold or a crevice of the channel protein, where the extracellular orifice of the sodium channel is located.

Dual action of endothelin-1 on the Ca2(+)-activated K+ channel in smooth muscle cells of porcine coronary artery

The effects of endothelin-1 (ET-1) on the activity of the large Ca2(+)-activated K+ channel (BK channel) in enzymatically dissociated smooth muscle cells of porcine coronary artery were studied with the cell-attached patch-clamp technique. ET-1 at concentrations between 0.1 and 10 nM potentiated the BK channel activity. This effect was maximal at 1 nM ET-1, resulting in an average of 4.2-fold increase in channel open-state probability as compared with control. ET-1 at concentrations higher than 10 nM produced an irreversible inhibition of the BK channel activity, primarily due to a marked decrease in the channel mean open-time. The activation by lower doses of ET-1, but not the inhibition by higher doses of ET-1, of the BK channel was blocked by 0.1 microM PN 200-110, a Ca2+ channel blocker. The modulation of the BK channel activity in smooth muscle cell membrane may be a possible mechanism for ET-induced vasodilator and vasoconstrictor actions.

Human papillomavirus type 16 nucleoprotein E7 is a tumor rejection antigen

It has been speculated that immunological mechanisms play an important role in the control of carcinomas associated with human papillomavirus (HPV), such as cervical cancers. We have now demonstrated that immunization of C3H/HeN mice by syngeneic nontumorigenic fibroblast-like cells that contain the transfected HPV-16 E7 gene conferred protection against transplanted cells from a HPV-16 E7-positive syngeneic tumor. This protection was HPV-16 E7-specific and was mediated by CD8+ lymphocytes, which presumably were cytotoxic T lymphocytes. These results indicate that tumor cells containing HPV-16 E7, either as a result of transfection, as in our studies, or naturally, as occurs in many human carcinomas, can induce a tumor-specific rejection response and serve as targets for such a response. The system described here provides an animal model to further study immune responses to HPV-associated malignancies and to test the efficacy of anti-HPV vaccines toward the therapy and prevention of such tumors.

Tumorigenic poxviruses: characterization of the expression of an epidermal growth factor related gene in Shope fibroma virus

The transcription and translation of an epidermal growth factor (EGF) related gene in the Leporipoxvirus Shope fibroma virus (SFV), termed the Shope fibroma growth factor (SFGF), have been characterized. Three early RNA transcripts complimentary to an anti-SFGF oligonucleotide were detected by Northern blot analysis, while no late transcripts were expressed. The activity of the SFGF early promoter was measured using a transient gene expression assay in SFV-infected cells using the bacterial choloramphenicol acetyltransferase as a reporter gene. Deletion analysis showed that the functional SFGF promoter domain is an AT-rich sequence contained within 30 bp of the major transcriptional initiation site as is typical of early poxvirus promoters. An intracellular form of the SFGF gene product was immunoprecipitated from infected lysates using rabbit antisera raised against a synthetic SFGF (amino acids 26-80). A 16-kDa product was detected, while in cells infected in the presence of tunicamycin, the immunoprecipitated product had a mobility on SDS-polyacrylamide gels of approximately 6 kDa, indicating that the SFGF gene product is extensively post-transcriptionally modified. The intracellular 16-kDa form can be pulse-chased to a 14-kDa form but the secreted form of SFGF could not be detected in the medium using this anti-peptide antiserum.

Processing, assembly, and immunogenicity of human immunodeficiency virus core antigens expressed by recombinant vaccinia virus

Recombinant vaccinia viruses that contained regions of the gag-pol open reading frames of human immunodeficiency virus type 1 (HIV-1) were constructed. Cells infected with recombinants containing both gag and protease genes expressed and processed HIV gag antigens efficiently. Processing was much reduced in cells infected with recombinants containing only gag, but not the protease gene. However, significant amounts of p41 were produced by protease-defective recombinants. This protein was immunoreactive with p24-specific monoclonal antibodies and was produced in a truncated form by a recombinant containing a 3' deletion in the p15 coding region of gag ORF. These results indicate that p41 could represent an alternative gag precursor with N-terminal sequences derived from p24 and C-terminal from p15. Ultrastructural analysis of recombinant-infected cells revealed that the gag antigens expressed were assembled into retrovirus-like particles and were secreted into culture medium. This assembly process was not dependent on HIV protease function, because immature core particles were produced by recombinants lacking HIV-1 protease functions. Immunization of mice and chimpanzees with vaccinia-HIVgag recombinant viruses generated both antibody and cell-mediated immune responses to HIV gag antigens. These recombinants are therefore useful not only for studying HIV virion processing and assembly, but also for designing immunogens for the prophylaxis and immunotherapy against AIDS.

Human immunodeficiency virus-like, nonreplicating, gag-env particles assemble in a recombinant vaccinia virus expression system

We report the assembly of human immunodeficiency virus (HIV)-like particles in African green monkey kidney cells coinfected with two recombinant vaccinia viruses, one carrying the HIV-1 gag and protease genes and the other the env gene. Biochemical analysis of particles sedimented from culture supernatants of doubly infected cells revealed that they were composed of gag proteins, primarily p24, as well as the env proteins gp120 and gp41. Thin-section immunoelectron microscopy showed that these particles were 100 to 120 nm in diameter, were characterized by the presence of cylindrical core structures, and displayed the mature gp120-gp41 complexes on their surfaces. Furthermore, thin-section immunoelectron microscopy analysis of infected cells showed that particle assembly and budding occurred at the plasma membrane. Nucleic acid hybridization suggested that the particles packaged only the gag mRNA but not the env mRNA. Therefore, the system we present is well suited for studies of HIV virion maturation. In addition, the HIV-like particles provide a novel and attractive approach for vaccine development.

Risk factor analysis of an epidemic of hepatitis A in a factory in Shanghai

Investigation of an epidemic of hepatitis A which occurred in Shanghai in early 1988 was conducted at the Shanghai No. 2 Yarn Dyeing and Weaving Mill. In this factory the attack rate between January and April 1988 was 9%. The rate was highest among staff who ate raw clams (18%) and higher among those who ate cooked clams (7%) than among those who did not eat clams (2%). In addition, independent risk factors for infection were: age below 30 years (relative risk (RR) = 3.0, 95% Cl: 2.0, 4.5) shift work (RR = 3.3, 95% Cl: 1.9, 5.8) and eating out (RR = 4.7, 95% Cl: 2.3, 9.7). Consumption of clams contaminated with hepatitis A was the main risk factor in this episode. The study indicates that strengthening surveillance of shellfish hygiene is important in preventing future epidemics of hepatitis A.

Alterations by glyburide of effects of BRL 34915 and P 1060 on contraction, 86Rb efflux and the maxi-K+ channel in rat portal vein

Effects of the K+ channel blocking agent, glyburide, on the actions of two K+ channel openers, BRL 34915 (cromakalim) and P 1060 (Leo), a potent pinacidil derivative (N-(t-butyl)-N"-cyano-N'-3-pyridyl-guanidine), were ascertained. Tension responses and 86Rb fluxes in rat portal vein strips and single channel electrophysiological recordings in enzymatically dissociated rat portal vein cells were obtained. Glyburide (0.3 microM) increased spontaneous contractile activity and caused concentration-dependent shifts in the relaxation responses to BRL 34915 and P 1060. Increases in 86Rb efflux were obtained only at much higher concentrations of BRL 34915 or P 1060, and these increases were blocked only at higher concentrations of glyburide (5.0 microM). BRL 34915 and P 1060 specifically increase the open-state probability of the Ca+(+)-activated K+ (maxi-K+) channel, and these actions are blocked by glyburide and also by charybdotoxin. Changes in single channel activity and contractile responsiveness occur at similar concentrations of agonists and antagonists. Thus, the membrane channel in rat portal vein affected by glyburide, BRL 34915 and P 1060 appears to be the Ca+(+)-activated maxi-K+ channel (that does not show ATP dependence under the conditions of these experiments). Concentrations of agonists and antagonists effective on maxi-K+ channel activity correspond to those affecting contractile responsiveness and are lower than those eliciting changes in 86Rb flux.

[A survey on the medicinal history of Pinellia ternata Breit]

The work in this paper has a twofold aim: 1 Verifying the Chinese drug "Banxia" in medicinal books before 1900 as the tuber of Pinellia ternata (Araceae), While P.ternata in Qizhou (Licheng County, Shandong Province) had been mistaken for P.tripartita which only grow in Japan; 2 proving young tuber of P.pedatisecta to be "Youba" which was confused with "Banxia" in some ancient medicinal books, while "Youba" has been regarded as Arisaema regens so far.

The Ca2+-activated K+ channel and its functional roles in smooth muscle cells of guinea pig taenia coli

Currents through single potassium channels were studied in cell-attached or inside-out patches from collagenase-dispersed smooth muscle cells of the guinea pig taenia coli. Under conditions mimicking the physiological state with [K+]i = 135 mM: [K+]o = 5.4 mM, three distinct types of K+ channel were identified with conductances around 0 mV of 147, 94, and 63 pS. The activities of the 94- and 63-pS channel were observed infrequently. The 147-pS channel was most abundant. It has a reversal potential of approximately -75 mV. It is sensitive to [Ca2+]i and to membrane potential. At -30 mV, the probability of a channel being open is at a minimum. At more positive voltages, the probability follows Boltzman distribution. A 10-fold change in [Ca2+]i causes a 25-mV negative shift of the voltage where half of the channels are open; an 11.3-mV change in membrane potential produces an e-fold increase in the probability of the channel being open when P is low. At voltages between -30 and -50 mV, the open probability increases in an anomalous manner because of a large decrease of the channel closed time without much change in the channel open time. This anomalous activity may play a regulatory role in maintaining the resting potential. The histograms of channel open and closed time fit well, respectively, with single and double exponential distributions. Upon step depolarizations by 100-ms pulses, the 147-pS channel opens with a brief delay. The delay shortens and both the number of open channels and the open time increase with increasing positivity of the potential. The averaged currents during the step depolarizations closely resemble the delayed rectifying outward K+ currents in whole-cell recordings.

Permeation, selectivity, and blockade of the Ca2+-activated potassium channel of the guinea pig taenia coli myocyte

The permeation properties of the 147-pS Ca2+-activated K+ channel of the taenia coli myocytes are similar to those of the delayed rectifier channel in other excitable membranes. It has a selectivity sequence of K+ 1.0 greater than Rb+ 0.65 greater than NH4+ 0.50. Na+, Cs+, Li+, and TEA+ (tetraethylammonium) are impermeant. Internal Na+ blocks K+ channel in a strongly voltage-dependent manner with an equivalent valence (zd) of 1.20. Blockade by internal Cs+ and TEA+ is less voltage dependent, with d of 0.61 and 0.13, and half-blockage concentrations of 88 and 31 mM, respectively. External TEA+ is about 100 times more effective in blocking the K+ channel. All these findings suggest that the 147-pS Ca2+-activated K+ channel in the taenia myocytes, which functions physiologically like the delayed rectifier, is the single-channel basis of the repolarizing current in an action potential.