Plasmolipin: genomic structure, chromosomal localization, protein expression pattern, and putative association with Bardet-Biedl syndrome

Plasmolipin is a membrane protein and belongs to the tetraspan molecule (4TM) family, an expanding group of myelin proteins many of which could be linked to human hereditary demyelinating neuropathies. We have cloned and sequenced the mouse plasmolipin gene, revealing the common organization of the 4TM gene group with four exons and a large first intron. Western blot analysis with an antibody raised against the C-terminal intracellular part of the protein showed that plasmolipin is expressed not only in the nervous system and kidney, but also in a number of other tissues such as thymus, testis, lung, and thyroid gland. By means of radiation hybrid mapping and FISH analysis, we could localize the human plasmolipin gene to Chromosome 16q13 within the putative region of the Bardet-Biedl syndrome type 2 (BBS2) gene locus. BBS2 is a clinically and genetically heterogeneous group of disorders resulting in rod-cone dystrophy, obesity, postaxial polydactyly, renal dysfunction, and mental retardation, which were very recently associated with a novel gene designated BBS2. With respect to intrafamiliar variations in the manifestation of BBS, we suggest that plasmolipin might be either another candidate gene or a modifier of the BBS2 phenotype.

Role of CD28 for the generation and expansion of antigen-specific CD8(+) T lymphocytes during infection with Listeria monocytogenes

Infection of mice with the intracellular bacterium Listeria monocytogenes results in a strong CD8(+) T cell response that is critical for efficient control of infection. We used CD28-deficient mice to characterize the function of CD28 during Listeria infection, with a main emphasis on Listeria-specific CD8(+) T cells. Frequencies and effector functions of these T cells were determined using MHC class I tetramers, single cell IFN-gamma production and Listeria-specific cytotoxicity. During primary Listeria infection of CD28(-/-) mice we observed significantly reduced numbers of Listeria-specific CD8(+) T cells and only marginal levels of specific IFN-gamma production and cytotoxicity. Although frequencies were also reduced in CD28(-/-) mice during secondary response, we detected a considerable population of Listeria-specific CD8(+) T cells in these mice. In parallel, IFN-gamma production and cytotoxicity were observed, revealing that Listeria-specific CD8(+) T cells in CD28(-/-) mice expressed normal effector functions. Consistent with their impaired CD8(+) T cell activation, CD28(-/-) mice suffered from exacerbated listeriosis both after primary and secondary infection. These results demonstrate participation of CD28 signaling in the generation and expansion of Ag-specific CD8(+) T cells in listeriosis. However, Ag-specific CD8(+) T cells generated in the absence of CD28 differentiated into normal effector and memory T cells.

Spin-dependent exciton formation in pi-conjugated compounds

The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 +/- 1 per cent for the monomer, but 57 +/- 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.

The energy gap law for triplet states in Pt-containing conjugated polymers and monomers

The energy gap law established for aromatic hydrocarbons and rare earth ions relates the nonradiative decay rate to the energy gap of a transition through a multiphonon emission process. We show that this energy gap law can be applied to the phosphoresce of a series of conjugated polymers and monomers for which the radiative decay rate has been enhanced through incorporation of a heavy metal. We find that the nonradiative decay rate from the triplet state T(1) increases exponentially with decreasing T(1)-S(0) gap for the polymers and monomers at 300 and 20 K. Comparison of the nonradiative decay of polymers with that of their corresponding monomers highlights the role of electron-lattice coupling.

Quantitative cytochemical analysis of glucose-6-phosphate dehydrogenase activity in living isolated hepatocytes of European flounder for rapid analysis of xenobiotic effects

There is a great need for rapid but reliable assays to determine quantitatively effects of xenobiotics on biological systems in environmental research. Hepatocytes of European flounder are sensitive to low-dose toxic stress. Glucose-6-phosphate dehydrogenase (G6PDH) is the major source of NADPH in cells and is therefore of major importance for NADPH-dependent xenobiotic biotransformation and defense against toxic injury. These facts prompted us to develop a sensitive cytochemical method to detect G6PDH activity in living isolated flounder hepatocytes using the tetrazolium salt method. The intact plasma membrane did not appear to be a barrier for substrate, co-enzyme, and dye molecules because the intracellular enzyme reaction started immediately when incubation medium was added and could be monitored in real time per individual cell using image analysis. The reaction was effectively stopped for end point measurements by using 4% formaldehyde in 0.1 M phosphate buffer (pH 5.3). The final reaction product, formazan, was stable in hepatocytes for at least 12 days at 4C. This is the first time that a chromogenic histochemical assay is applied to living cells. This approach provides an easy tool for large-scale screening of xenobiotic metabolism and cellular stress defense.

The axial channel of the proteasome core particle is gated by the Rpt2 ATPase and controls both substrate entry and product release

Substrates enter the proteasome core particle (CP) through a channel that opens upon association with the regulatory particle (RP). Using yeast mutants, we show that channel opening is mediated by the ATPase domain of Rpt2, one of six ATPases in the RP. To test whether degradation products exit through this channel, we analyzed their size distribution. Their median length from an open-channel CP mutant was 40% greater than that from the wild-type. Thus, channel opening may enhance the yield of peptides long enough to function in antigen presentation. These experiments demonstrate that gating of the RP channel controls both substrate entry and product release, and is specifically regulated by an ATPase in the base of the RP.

IL-4 determines eicosanoid formation in dendritic cells by down-regulation of 5-lipoxygenase and up-regulation of 15-lipoxygenase 1 expression

Dendritic cell (DC) differentiation from human CD34(+) hematopoietic progenitor cells (HPCs) can be triggered in vitro by a combination of cytokines consisting of stem cell factor, granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor alpha. The immune response regulatory cytokines, IL-4 and IL-13, promote DC maturation from HPCs, induce monocyte-DC transdifferentiation, and selectively up-regulate 15-lipoxygenase 1 (15-LO-1) in blood monocytes. To gain more insight into cytokine-regulated eicosanoid production in DCs we studied the effects of IL-4/IL-13 on LO expression during DC differentiation. In the absence of IL-4, DCs that had been generated from CD34(+) HPCs in response to stem cell factor/granulocyte-macrophage colonystimulating factor/tumor necrosis factor alpha expressed high levels of 5-LO and 5-LO activating protein. However, a small subpopulation of eosinophil peroxidase(+) (EOS-PX) cells significantly expressed 15-LO-1. Addition of IL-4 to differentiating DCs led to a marked and selective down-regulation of 5-LO but not of 5-LO activating protein in DCs and in EOS-PX(+) cells and, when added at the onset of DC differentiation, also prevented 5-LO up-regulation. Similar effects were observed during IL-4- or IL-13-dependent monocyte-DC transdifferentiation. Down-regulation of 5-LO was accompanied by up-regulation of 15-LO-1, yielding 15-LO-1(+) 5-LO-deficient DCs. However, transforming growth factor beta1 counteracted the IL-4-dependent inhibition of 5-LO but only minimally affected 15-LO-1 up-regulation. Thus, transforming growth factor beta1 plus IL-4 yielded large mature DCs that coexpress both LOs. Localization of 5-LO in the nucleus and of 15-LO-1 in the cytosol was maintained at all cytokine combinations in all DC phenotypes and in EOS-PX(+) cells. In the absence of IL-4, major eicosanoids of CD34(+)-derived DCs were 5S-hydroxyeicosatetraenoic acid (5S-HETE) and leukotriene B(4), whereas the major eicosanoids of IL-4-treated DCs were 15S-HETE and 5S-15S-diHETE. These actions of IL-4/IL-13 reveal a paradigm of eicosanoid formation consisting of the inhibition of one and the stimulation of another LO in a single leukocyte lineage.

[Tetanus--differential diagnosis of cerebrovascular stroke]

Report about a 80 year-old female patient admitted to hospital with dysarthria and dysphagia suspected to have had a stroke. The symptoms however were caused by a tetanus infection consequent upon a grossly contaminated ten-day-old wound. Since particularly geriatric patients are at risk of tetanus infections in industrialised countries, such patients ought to get regular booster-vaccinations.

The value of posterior levator repair in the treatment of anorectal incontinence due to rectal prolapse--a clinical and manometric study

BACKGROUND

When treating a complete rectal prolapse, the most important objective is elimination of the prolapse. In addition, restoration of sufficient anorectal continence is extremely important for the patients. We examined the value of posterior levator repair with respect to stabilization of the pelvic floor and to improvement in anorectal incontinence.

METHODS

In patients with disabling anorectal incontinence, a posterior levatorplasty can be concomitantly performed during operative removal of the prolapse. To facilitate evaluation of the operative results, we implemented a scoring system to judge the patients' subjective symptoms of incontinence; in addition, we performed manometric measurements of resting and squeezing pressures of the anal sphincter to objectify the anorectal incontinence.

RESULTS

From 1991 to 1997, 84 patients (mean age 65+/-10 years, 38-91 years; 79 women, 5 men) with complete rectal prolapse and severe incontinence were operatively treated; corresponding follow-ups were done. The following procedures were performed: Frykmann-Goldberg, 28 patients; Wells, 18 patients; Ripstein, 22 patients; and perineal proctectomy, 16 patients. Incontinence for liquid and solid stools was present in all of these patients. Posterior levatorplasty was implemented in 38 patients, and in this group we found significantly better postoperative results, both clinically and in the manometric measurements. Continence was improved by 84% in the group with levatorplasty, but improvement was only 67% in the other group (P<0.05). The incontinence score decreased significantly in the group with levatorplasty (preoperative 16.4+/-3.1, postoperative 9.3+/-4.5, P<0.05, vs the other group with preoperative 15.6+/-4.2, postoperative 11.5+/-5.1). Manometric observations in the group with levatorplasty demonstrated 55% improvement in resting pressure (preoperative 29+/-17 cm H2O, postoperative 45+/-21 cm H2O, P<0.05) and 40% improvement in squeezing pressure (preoperative 61+/-25 cm H2O, postoperative 85+/-31 cm H2O, P<0.05). In the group without levatorplasty, resting and squeezing pressure improved only by 20% (resting pressure: preoperative 32+/-16 cm H2O, postoperative 38+/-18 cm H2O; squeezing pressure: preoperative 64+/-29 cm H2O, postoperative 75+/-26 cm H2O).

CONCLUSIONS

Posterior levatorplasty is an easy and efficient operative procedure which facilitates an improvement in anorectal continence. There are no apparent disadvantages. For this reason, levatorplasty can be part of operative procedures implemented in the treatment of a complete rectal prolapse accompanied by disabling anorectal incontinence.

Diagnostic value of DNA image cytometry in ulcerative colitis

The increased risk of colorectal cancer in patients with extensive, long-standing ulcerative colitis is well established. The interpretation of dysplasia as the common precursor lesion of colorectal cancer in ulcerative colitis is, however, subject to inter- and intraobserver variation. The histologic diagnosis is particularly difficult in the presence of acute inflammation. Therefore, the analysis of ploidy patterns might be a more objective diagnostic tool. In the present study, the correlation of ploidy and dysplasia of the colonic mucosa was evaluated in the absence and presence of inflammation. Image cytometry was performed on 561 fixed, paraffin-embedded tissue specimens from 67 patients with ulcerative colitis. Twenty patients had long-standing and extensive disease, including eight patients in whom the colitis was associated with colorectal cancer. Dysplasia was only found in patients with long-standing colitis or with colorectal cancer and was significantly more often diagnosed in the case of concomitant inflammation. On the other hand, aneuploid patterns were shown to occur independent of inflammatory activity. Aneuploidy was present in all colorectal carcinomas associated with ulcerative colitis and in 46.2% of specimens with dysplasia. Moreover, aneuploidy was detectable in four of 12 samples with low-grade dysplasia as well as in one case devoid of any dysplastic alteration. Ulcerative colitis patients with low-grade dysplasia plus aneuploidy probably represent a subgroup that might be at higher risk of developing colorectal cancer than patients with low-grade dysplasia alone. All in all, image cytometry analysis might be instrumental in identifying neoplastic lesions even in cases of increased inflammatory activity or regenerative change.

The substrate translocation channel of the proteasome

The core particle (CP) of the yeast proteasome is composed of four heptameric rings of subunits arranged in a hollow, barrel-like structure. We have found that the CP is autoinhibited by the N-terminal tails of the outer (alpha) ring subunits. Crystallographic analysis showed that deletion of the tail of the alpha3 subunit opens a channel into the proteolytically active interior chamber of the CP, thus derepressing peptide hydrolysis. In the latent state of the particle, the tails prevent substrate entry by imposing topological closure on the CP. Inhibition by the alpha subunit tails is relieved upon binding of the regulatory particle to the CP to form the proteasome holoenzyme. Opening of the CP channel by assembly of the holoenzyme is regulated by the ATPase domain of Rpt2, one of 17 subunits in the RP. Thus, open-channel mutations in CP subunits suppress the closed-channel phenotype of an rpt2 mutant. These results identify a specific mechanism for allosteric regulation of the CP by the RP.

A gated channel into the proteasome core particle

The core particle (CP) of the yeast proteasome is composed of four heptameric rings of subunits arranged in a hollow, barrel-like structure. We report that the CP is autoinhibited by the N-terminal tails of the outer (alpha) ring subunits. Crystallographic analysis showed that deletion of the tail of the alpha 3-subunit opens a channel into the proteolytically active interior chamber of the CP, thus derepressing peptide hydrolysis. In the latent state of the particle, the tails prevent substrate entry by imposing topological closure on the CP. Inhibition by the alpha-subunit tails is relieved upon binding of the regulatory particle to the CP to form the proteasome holoenzyme.

Comparative localization of cathepsin B protein and activity in colorectal cancer

Cathepsin B is a lysosomal cysteine proteinase that may participate in cancer progression. We compared localization of its protein and activity during progression of human colorectal cancer. In adenomas and carcinomas, protein expression and, particularly, activity were elevated compared with those in normal colorectal mucosa. In normal mucosa, cathepsin B protein expression was moderate in stroma and variable in epithelium, whereas activity was mainly present in distinct areas of stroma directly underneath the surface of the colon and in epithelium at the surface of the colon. Stroma in adenomas and carcinomas contained moderate to high protein levels but little activity except for areas of angiogenesis, inflammation, and necrosis, in which activity was high. In adenomas and the majority of well-differentiated carcinomas and moderately differentiated carcinomas, cathepsin B protein and activity were found in granular form in the epithelium, close to the basement membrane. Protein and activity levels were low and diffusely distributed in cancer cells in the remainder of the well-differentiated and moderately differentiated carcinomas and in all poorly differentiated carcinomas. Invasive fronts in most cancers contained moderate protein levels but high activity. We conclude that (a) activity localization is essential to understand the role of cathepsin B in cancer progression, and (b) cathepsin B activity in human colon is associated with invasion of cancer cells, endothelial cells, and inflammatory cells, and in cell death, both apoptotic and necrotic.

Molecular cloning of a SALL1-related pseudogene and mapping to chromosome Xp11.2

SALL1 and SALL2 have been identified as two human homologs of the region-specific homeotic gene spalt (sal) of Drosophila, which encodes a zinc finger protein of characteristic structure. SALL1 has recently been found to be mutated in patients with Townes-Brocks syndrome (TBS, OMIM No. 107480). Here we report the isolation and mapping of another sal-like human gene, named SALL1P, on chromosome Xp11.2. This intronless gene closely resembles SALL1 but displays several mutations, suggesting that SALL1P represents a sal-related pseudogene. The high similarity of SALL1P to SALL1 is of considerable importance for mutation analysis of SALL1 in TBS.

Direct comparison of the sensitivity of enzyme histochemical and immunohistochemical methods: cathepsin B expression in human colorectal mucosa

Immunohistochemical localization of the proteinase cathepsin B has been compared directly with localization of cathepsin B activity with a catalytic (enzyme) histochemical method. The 2 approaches demonstrate principally different aspects of an enzyme. The immunohistochemical method localizes the enzyme protein whether it is active or not whereas the catalytic method visualizes the functionally active enzyme only. Sensitivity of both approaches to localize low amounts of enzyme protein or activity has never been compared. In the present study, we show that cathepsin B protein has a wider distribution pattern than cathepsin B activity in human colorectal mucosa, which means that inactive cathepsin B protein is present. With respect to sensitivity of the methods, it is shown that cathepsin B protein could only be demonstrated properly when strong signal amplification was applied by using Nanogold with silver enhancement, whereas activity could be demonstrated with a simple and direct fluorogenic histochemical assay. It is concluded that catalytic histochemical methods are relatively simple methods for the localization of activity of enzymes in tissues and cells and that their sensitivity is high in comparison with immunohistochemical methods.

Signal amplification in immunohistochemistry at the light microscopic level using biotinylated tyramide and nanogold-silver staining

Signal amplification techniques greatly enhance the sensitivity of immunohistochemical (IHC) and in situ hybridization (ISH) methods. In particular, catalyzed signal amplification (CSA) using labeled tyramide or Nanogold-silver staining is an important signal amplification tool. We have applied a combination of both techniques, as has been introduced for ISH, for a further increase in sensitivity of an IHC method to detect cathepsin B. This lysosomal proteinase can also be expressed extracellularly, particularly in relation to cancer metastasis. Higher sensitivity of the IHC method was needed because existing methods failed to demonstrate cathepsin B protein where cathepsin B activity was found with a fluorescence enzyme histochemical method. Combined CSA and Nanogold-silver staining provided the sensitivity that was required. Moreover, this signal amplification method enabled the use of a 10-fold lower concentration of primary antibody (1 microg/ml). Nonspecific background staining was low provided that endogenous biotin, avidin, and peroxidase were completely blocked. The method was reproducible when all steps, and particularly the silver enhancement step, were rigidly controlled. The method resulted in localization patterns of cathepsin B protein that were in agreement with those of cathepsin B activity in serial sections of rat liver containing colon cancer metastases. We concluded that combined application of CSA and Nanogold-silver staining provides high sensitivity for immunohistochemical methods and that activity localization by an enzyme histochemical method is a very attractive alternative to IHC localization of an enzyme because it is at least as sensitive, it is rapid and simple, and it provides direct information on the function of an enzyme.

Short-time induction of oxidative stress in hepatocytes of the European flounder (Platichthys flesus)

Oxidative stress induced by xenobiotic compounds has been studied using primary hepatocytes of juvenile European flounder (Platichthys flesus L.) caught in a low polluted area of the German Bight, Tiefe Rinne (Landwüst et al., 1996.). Cells were exposed to known oxidative stressors such as hydrogen peroxide and benzo[a]pyrene (B[a]p) in various concentrations (50 and 100 microM) up to 6 days. Cell mortality was determined using fluorescent ethidium homodimer-1 and calcein AM. Oxidative stress response was measured by image analysis using dihydrorhodamine 123, which is converted to fluorescent rhodamine 123 in the presence of intracellular ROS. Oxyradical formation was initiated already after 2 h of exposure to low concentrations of B[a]p and hydrogen peroxide. Probably due to a membrane stabilising effect of the serum factors the addition of fetal bovine serum to the culture medium had a protecting influence on the hepatocytes and resulted in (1) an increased cell viability and (2) reduced formation of intracellular ROS during exposure. In conclusion, the assay is a sensitive tool for testing the potential of various xenobiotics to induce oxidative stress in living hepatocytes.

[Sporotrichosis--fixed cutaneous and lymphocutaneous form]

Two patients were infected with sporotrichosis; one had the fixed cutaneous form, the other the lymphocutaneous form. Sporotrichosis schenckii was identified in both with a culture from a tissue biopsy. Both patients were successfully treated with itraconazole, one received 100 mg and the other 200 mg itraconazole daily over a 3 months period.

Analysis of mutations in the p53 tumor suppressor gene and Ki- and Ha-ras proto-oncogenes in hepatic tumors of European flounder (Platichthys flesus)

DNA from five tumors, three other-injured livers and two normal liver tissue samples from the European flounder were analyzed for mutations in exons 5-8 of the tumor suppressor gene p53 and at codons 12, 13 and 61 of Ha- and Ki-ras proto-oncogenes. No tumor-specific mutations were identified by direct sequencing and single-strand conformation polymorphism of these genes. A number of silent polymorphisms were noted in p53. In addition to a need for more extensive analyses of flounder liver tumor samples for ras or p53 mutations, other cancer-related genes should be investigated.

Long-term results of low anterior resection with intersphincteric anastomosis in carcinoma of the lower one-third of the rectum: analysis of 31 patients

INTRODUCTION

Between 1985 and 1996, 190 patients underwent a low anterior rectal resection with coloanal anastomosis for adenocarcinoma of the lower one-third of the rectum.

METHODS

This article reports on 31 (17 males) of these patients with a very low localization of the tumor (distal tumor margin 1.3 +/- 0.9 cm above the dentate line). If the function of the sphincter was acceptable and we could exclude tumor infiltration into the sphincter through endosonography, we relocated the resection plane distally into the intersphincteric region to attain an acceptable margin of safety. In all of these cases, it was impossible for us to perform the usual surgical procedure of a mechanical anastomosis by means of a circular stapler. After intersphincteric rectal resection, the anastomosis was handsewn, using interrupted sutures from the perineal approach, 2.5 to 3 cm above the anal verge, implementing Parks' retractor. A protective stoma was performed in all cases. All data were documented prospectively.

RESULTS

COMPLICATIONS

Postoperative mortality was 0 percent. Postoperatively, none of the patients showed an indication for relaparotomy. The leakage rate was 48 percent. Only 16 percent later needed additional surgery for anastomotic strictures or for rectovaginal fistulas. Long-term observations showed that the anastomosis healed well in 27 patients (87.1 percent). Four patients (12.9 percent) decided to have a terminal colostomy performed (anastomotic stricture, 3 patients; anorectal incontinence, 1 patient).

FOLLOW-UP

During the follow-up period of 6.8 +/- 3.7 years, six patients (19.4 percent) developed a tumor progression (9.7 percent local recurrences and 12.9 percent distant spread). The five-year survival rate was 79 percent (Dukes A, 100 percent (n = 18); Dukes B, 67 percent (n = 4); and Dukes C, 44 percent (n = 9)). Continence: One-third of patients developed anorectal incontinence for liquid (29.6 percent) or solid stool (3.7 percent). Average stool frequency was 3.3 times per day. Resting pressure decreased significantly by 29 percent (preoperative, 105 +/- 37 cm H2O and postoperative, 75 +/- 19 cm H2O; P < 0.05), whereas squeeze pressure did not change.

CONCLUSION

In selected patients with tumors close to the dentate line, an intersphincteric resection of the rectum may help to avoid an abdominoperineal excision of the rectum with a terminal stoma, without any curtailment of oncologic standards. A protective stoma for three months is advantageous.

Substantial in vivo proliferation of CD4(+) and CD8(+) T lymphocytes during secondary Listeria monocytogenes infection

In mice Listeria monocytogenes infection induces a strong T cell response. In an attempt to quantitatively analyze the magnitude and kinetics of the CD4(+) and CD8(+) T cell response during L. monocytogenes infection in vivo we used a T cell transfer system that is independent of in vitro cell culture techniques and information about the identity of immunogenic T cell epitopes. Our results demonstrate substantial expansion of the in vivo primed and transferred T cell populations in response to L. monocytogenes. At the peak of response, transferred T cells represented more than one third of the total CD4(+) and CD8(+) T cell populations in blood and spleen of recipient mice. After stimulation in vitro, 40 % of these CD4(+) T cells responded to heat-killed listeriae with the production of IFN-gamma. Thus, our results reveal that in addition to the large CD8(+) T cell population an almost equally large population of Listeria-reactive CD4(+) T cells is generated in response to L. monocytogenes infection.

T-Type and tetrodotoxin-sensitive Ca(2+) currents coexist in guinea pig ventricular myocytes and are both blocked by mibefradil

Under Na(+)-free conditions, low-voltage-activated Ca(2+) currents in cardiomyocytes from various species have been described either as Ni(2+)-sensitive T-type Ca(2+) current (I(Ca(T))) or as tetrodotoxin (TTX)-sensitive Ca(2+) current (I(Ca(TTX))). So far, coexistence of the 2 currents within the same type of myocyte has never been reported. We describe experimental conditions under which I(Ca(T)) and I(Ca(TTX)) can be separated and studied in the same cell. Rat and guinea pig ventricular myocytes were investigated with the whole-cell voltage-clamp technique in Na(+)-free solutions. Whereas rat myocytes lack I(Ca(T)) and exhibit I(Ca(TTX)) only, guinea pig myocytes possess both of these low-voltage-activated Ca(2+) currents, which are separated pharmacologically by superfusion with TTX or Ni(2+). I(Ca(T)) and I(Ca(TTX)) were of similar amplitude but significantly differed in their electrophysiological properties: I(Ca(TTX)) activated at more negative potentials than did I(Ca(T)), the potential for half-maximum steady-state inactivation was more negative, and current deactivation and recovery from inactivation were faster. I(Ca(TTX)) but not I(Ca(T)) increased after membrane rupture ("run-up"). Isolation of I(Ca(TTX)) by application of the bivalent cation Ni(2+) is critical because of possible shifts in voltage dependence. Therefore, we investigated whether the T-type Ca(2+) channel blocker mibefradil (10 micromol/L) is a suitable tool for the study of I(Ca(TTX)). However, mibefradil not only blocked I(Ca(T)) by 85+/-2% but also decreased I(Ca(TTX)) by 48+/-8%. We conclude that under Na(+)-free conditions I(Ca(T)) and I(Ca(TTX)) coexist in guinea pig ventricular myocytes and that both currents are sensitive to mibefradil. Future investigations of I(Ca(T)) will have to consider the TTX-sensitive current component to avoid possible interference.

Cutting edge: role of B lymphocytes in protective immunity against Salmonella typhimurium infection

Infection of mice with Salmonella typhimurium gives rise to a disease similar to human typhoid fever caused by S. typhi. Since S. typhimurium is a facultative intracellular bacterium, the requirement of B cells in the immune response against S. typhimurium is a longstanding matter of debate. By infecting mice on a susceptible background and deficient in B cells (Igmu-/- mice) with different strains of S. typhimurium, we could for the first time formally clarify the role of B cells in the response against S. typhimurium. Compared with Igmu+/+ mice, LD50 values in Igmu-/- mice were reduced during primary, and particularly secondary, oral infection with virulent S. typhimurium. After systemic infection, Igmu-/- mice cleared attenuated aroA- S. typhimurium, but vaccine-induced protection against systemic infection with virulent S. typhimurium involved both B cell-dependent and -independent effector mechanisms. Thus, B cell-mediated immunity plays a distinct role in control of S. typhimurium in susceptible mice.