Nitrile hydratase involved in aldoxime metabolism from Rhodococcus sp. strain YH3-3 purification and characterization

Nitrile hydratase responsible for aldoxime metabolism from the E-pyridine-3-aldoxime degrading bacterium, Rhodococcus sp. strain YH3-3 was purified and characterized. Addition of cobalt ion was necessary for the formation of enzyme. The enzyme activity was highly induced not only by nitriles and amides but also by several aldoxime compounds. The enzyme was purified approximately 108-fold with a 16% yield from the cell-free extract of the strain. The native enzyme had a Mr of approximately 130 000 and consisted of two subunits (alpha-subunit, 27 100; beta-subunit, 34 500). The enzyme contained approximately 2 mol cobalt per mol enzyme; it showed a maximum activity at 60 degrees C and at 40 degrees C under the rate assay and end-point assay conditions, respectively, and was stable over a wide range of pH (pH 2.5-11.0). The enzyme had a wide substrate specificity: it acted on aliphatic saturated and unsaturated as well as aromatic nitriles. The N-terminus of the beta-subunit showed good sequence similarities with those of other nitrile hydratases. Nitrile hydratase is part of the metabolic pathway for aldoximes in microorganisms.

A novel selective nucleoside phosphorylating enzyme from Morganella morganii

A selective nucleoside phosphorylating enzyme was purified to homogeneity from Morganella morganii NCIMB10466 crude extract. The enzyme appeared to consist of six subunits identical in molecular mass (M(r) 25,000). It phosphorylated various nucleosides at the 5'-position to produce nucleoside-5'-monophosphates using pyrophosphate as the phosphate source. Energy-rich compounds, such as carbamylphosphate and acetylphosphate, were also very effective phosphate donors. The enzyme also exhibited phosphatase activity, and dephosphorylated various phosphate esters, but had a weak effect on nucleoside-3'-monophosphates. Based on the results of the kinetic study, the enzyme appeared to be an acid phosphatase. Its activity was partly inhibited by sulfhydryl reagents and heavy metal ions, but not by chelating reagents such as EDTA. Using the purified enzyme, 32.6 mM 5'-IMP was synthesized from inosine with a 41% molar yield, but the synthesized 5'-IMP was hydrolyzed back to inosine and phosphate as the reaction time was extended.

Effect of interleukin 10 on the hematopoietic progenitor cells from patients with aplastic anemia

The overproduction of cytokines with inhibitory effects on hematopoiesis is considered to play a role in the pathogenesis of aplastic anemia. While interleukin 10 (IL-10) is a cytokine production inhibitory factor, the possibility of immunosuppressive therapy using IL-10 for aplastic anemia has not been explored. In this study, therefore, we examined the effect of IL-10 on progenitor cells obtained from seven patients with severe aplastic anemia. Our study indicated that IL-10 dramatically enhanced the erythroid colony formation in a dose-dependent manner in two of the seven cases examined. When we examined the concentration of cytokines in the culture supernatants of unstimulated bone marrow cells, the spontaneous production of interferon-gamma (IFN-gamma) was observed in one of these two cases, and this production was completely inhibited by addition of IL-10. These findings suggested that IL-10 enhanced the erythroid colony formation by inhibiting the pathological production of IFN-gamma in this case. This study provides an experimental support for the clinical application of IL-10 in some patients with aplastic anemia.

Aortoduodenal fistula arising from the dilatation of a knitted Dacron graft: report of a case

A fatal aortoduodenal fistula occurred in a 72-year-old man who underwent a repair of an abdominal aortic aneurysm 16 years previously with a 20 x 10 mm bifurcated knitted Dacron graft. The aortic part of his bifurcated graft had dilated to 40 mm in diameter, with a discrepancy of 20 mm in the diameter between the graft and infrarenal aorta. The fourth portion of the duodenum adhered to the left side of the anastomosis, where the aortoenteric fistula had occurred. We believe that the graft dilatation was the cause of the anastomotic failure, although other factors such as atherosclerotic degeneration of the host aorta should also be considered. Knitted Dacron grafts that have been implanted for more than 10 years should therefore be monitored carefully because they have an inherent tendency to dilate, especially those manufactured before 1981.

Monoclonal antibody to human midkine reveals increased midkine expression in human brain tumors

We produced a rat IgG2a monoclonal antibody against the carboxyl terminal region of human midkine (MK), a novel growth factor. This monoclonal antibody was used in immunohistochemical studies to compare the expression of MK, proliferating cell nuclear antigen (PCNA) and p53 protein in 133 primary brain tumors and 21 carcinoma metastases to the central nervous system. Approximately half of the glioblastomas multiforme (GBMs) (19/32), medulloblastomas (8/14), primitive neuroectodermal tumors (PNETs) (5/11), breast carcinoma metastases (Br-Mts) (6/10) and lung carcinoma metastases (L-Mts) (5/11) as well as some astrocytomas (2/14) had tumor cells that expressed MK; however, oligodendrogliomas, ependymomas, schwannomas, meningiomas, and pituitary adenomas did not express MK. The values of the PCNA-labeling index were statistically higher in GBMs, medulloblastomas, PNETs, Br-Mts, and L-Mts that expressed MK than in those that did not (Wilcoxon rank-sum test, p < 0.05). There was no correlation between MK and p53 protein in all tumor types. Normal and non-neoplastic brain tissues were negative for MK, PCNA, and p53 protein. We conclude that primary and metastatic tumors of the brain express MK and that the MK expression in brain tumors may depend, in part, on the proliferating potential.

Ventriculoatrial shortening achieved in Wolff-Parkinson-White syndrome by programmed right ventricular pacing

A 47-year-old woman with a left-sided Kent bundle showed marked reduction of the ventriculoatrial conduction time during extrastimuli at the right ventricular apex and outflow tract. The degree of reduction was greater than 6 years ago. A 'supernormal conduction' in the ventricle and the Kent bundle could have been responsible for this phenomenon.

[Bacteriological and clinical break points: evaluation of the usefulness of cefozopran based on MIC]

Drug sensitivity of clinically isolated bacteria to cefozopran (CZOP), which is a new cephem antibiotic, was investigated, and the usefulness of the drug was evaluated from the viewpoint of bacteriological and clinical (pneumonia) break points. The following results were obtained. 1. According to bacteriological break points, methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus spp. showed low sensitivity to cefozopran (CZOP). However, the sensitivity of methicillin-sensitive Staphylococcus aureus (MSSA), E. coli, and Klebsiella spp., which are often isolated as pathogens of common infections, was 100%, that of Enterobacter spp., Serratia sp., and Citrobacter sp. was 90% or higher, and that of Pseudomonas aeruginosa was 80% or higher; the values were comparable to or better than those for ceftazidime (CAZ). These results suggest a expanded antibacterial spectrum and enhanced antibacterial potency of CZOP. 2. The estimated response rate of pneumonia to CZOP was 87.5% in outpatients and 51.9% in inpatients. Therefore, CZOP is considered to be one of the first choices especially in outpatient empiric therapy.

Spread of varicella-zoster virus DNA to family members and environments from siblings with varicella in a household

OBJECTIVE

To elucidate virus spread from siblings with varicella to other family members and environmental objects in a family setting before and after onset of the disease.

MATERIALS AND METHODS

Among a family consisting of five members, a boy developed varicella and the remaining two siblings developed the disease 17 and 18 days after onset of the index case. Swab samples from throats and hands of parents and three siblings and samples from several sources in the environment of the house were collected frequently before and/or after onset of the disease. Varicella-zoster virus (VZV) DNA in the samples was examined by a sensitive polymerase chain reaction amplification assay.

RESULTS

In total, 108 samples from the throats and hands of the three children with varicella, 72 such samples from parents, and 72 samples from the surfaces of several sources in the house were collected. Eight days after onset of the index case (the older boy), VZV DNA was detected in both samples from the index case and on the surfaces of four sources (air conditioner filter, table, television channel push-buttons, and door handle), but not from the two other siblings or parents. Then, it was detected once on the mother's hand and the air conditioner filter and three times on the television channel push-buttons by January 30, 1998, when the girl developed varicella, 17 days after onset of the index case. The younger brother developed the disease on January 31. Viral DNA could not be detected in any samples obtained on January 30; however, it was detected on the hands of the older boy and the father and in samples from the hand and throat of the girl on January 31. Thereafter, virus DNA was detected three times intermittently by February 13 on the hand and three times persistently in the throat of the girl. The virus DNA was detected three times between February 1 and 3 on the hand and three times between February 1 and 4 in the throat of the younger boy. It was detected occasionally on the hands of the older boy and the parents, and occasionally or intermittently on surfaces of four environmental sources between February 2 and 13.

CONCLUSIONS

The present study showed the rapid and broad contamination of the environment with the VZV DNA when the varicella patient appeared in a family, although it does not directly mean infectivity.

The effect of EGF on electrolyte transport is mediated by tyrosine kinases in the rabbit cortical collecting duct

Epidermal growth factor (EGF) inhibits amiloride-sensitive Na(+) conductance in the apical membrane of the isolated rabbit cortical collecting duct. However, there is no information on the relationship between electrolyte transport and tyrosine kinase. We examined the effect of EGF on transport of potassium and chloride as well as sodium and the roles of tyrosine kinases in the rabbit cortical collecting duct using in vitro isolated tubular microperfusion. Basolateral EGF depolarized the transepithelial voltage in a dose-dependent manner within a concentration range of 10(-10) in 10(-8) M. Basolateral ouabain and luminal amiloride completely abolished EGF-induced depolarization. However, luminal BaCl(2) did not abolish its depolarization. To confirm the mechanism, sodium, potassium, and chloride fluxes were measured in the presence of 10(-10) M EGF. EGF significantly decreased the lumen-to-bath isotope flux of sodium and chloride from 93.6+/-12.5 to 61.1+/-9.6 pmol/mm/min (n = 5, p<0.05) and from 86.6+/-10.0 to 54. 8+/-9.7 pmol/mm/min (n = 10, p<0.01), respectively. EGF also decreased net potassium secretion from -27.7+/-5.9 to -7.8+/-1.5 pmol/mm/min (n = 6, p<0.01). To examine whether EGF-induced depolarization is mediated by tyrosine kinase, tyrosine kinase inhibitors were applied from the basolateral side. Pretreatment with 1 microg/ml herbimycin A for 120 min completely abolished EGF-induced depolarization (90.9+/-5.4%, n = 4; NS). Herbimycin A itself also did not change the lumen-to-bath isotope flux of sodium and completely abolished the inhibition of Na(+) absorption on EGF action (control 65.4+/-6.8, herbimycin A 61.8+/-6.3, EGF with herbimycin A 60.0+/-4.4 pmol/min/mm, n = 5; NS). In conclusion, EGF depolarizes transepithelial voltage by inhibiting sodium transport primarily and potassium and chloride transport secondarily. These effects were blocked by nonspecific tyrosine kinase inhibitors.

Altered immune response of interferon regulatory factor 1-deficient mice against Plasmodium berghei blood-stage malaria infection

Nitric oxide (NO) is a short-lived biological mediator which can be induced in various cell types and is able to cause many metabolic changes in target cells. Inhibition of tumor cell growth and antimicrobial activity has been attributed to the stimulation of NO production by transcriptional upregulation of inducible nitric oxide synthase. In the present study, we used mice devoid of functional interferon regulatory factor 1 by targeted gene disruption (IRF-1(-/-)) to investigate the role of NO in the host immune response against blood-stage Plasmodium berghei ANKA infection. IRF-1(-/-) mice survived longer with a later onset of and a lower peak parasitemia despite the inability to produce appreciable levels of NO. The administration of exogenous interleukin-12 (IL-12) was able to prolong survival in the wild-type mice with an upregulation in the expression of both gamma interferon (IFN-gamma) and NO. However, the administration of IL-12 did not improve the survival of IRF-1(-/-) mice. These studies indicate that while IL-12 is able to mediate protection via an IFN-gamma- and NO-dependent pathway in the wild-type mice, such a protective mechanism may not be functional in the IRF-1(-/-) mice. Our results suggest that NO may not be essential for host immunity to the parasite and that IRF-1(-/-) mice are able to induce an IFN-gamma- and NO-independent mechanism against P. berghei infection.

The characterization of human brain tumor using magnetization transfer technique in magnetic resonance imaging

The clinical applicability of magnetization transfer (MT) technique in magnetic resonance imaging (MRI) for the estimation of the histological and constitutional feature of brain tumors was investigated. MT effect was evaluated by measuring the MT ratio (MTR). The parameters in 1.5-tesla MRI system were as follows: TR, 50 msec; TE, 5 msec; flip angle, 30 degree; offset frequency of off-resonance MT pulse, 1000 Hz. The sequence was performed in 20 normal volunteers and 45 patients with brain tumors which were characterized histologically and surgically. The MTR for brain tumors was significantly lower than that for normal brain tissue (p < 0.05). The MTR for meningioma was higher than that for the other brain tumors (p < 0.05). In the meningiomas, MTR for fibrous type was higher than that for meningothelial type, but there was no statistical significance. Regarding the physical consistency for the brain tumors, as classified by surgery, there was a statistically significant difference in MTR between the soft tumor group (0.22 +/- 0.03, n = 6) and the hard tumor group (0.36 +/- 0.04, n = 10) (p < 0.01). This study suggested that the MT technique for patients with brain tumor may be useful to understand the characteristics of the tumors presurgically, based on the degree of intermolecular interaction of macromolecule such as protein.

[Factors related to the QT prolongation in chronic renal failure]

QT prolongation, a risk factor for arrhythmia and cardiac death, is observed in uremic patients. Though hypocalcemia, autonomic nerve dysfunction and cardiac hypertrophy are assumed to cause the uremic QT prolongation, the exact mechanism remains unspecified. We therefore examined factors related to the QT interval in chronic renal failure (CRF). Corrected QT interval (QTc) was significantly prolonged in CRF just before the induction of dialysis therapy (group A) compared with nephrotic syndrome with the intact or mildly impaired renal function (group B). QTc was also prolonged in acute renal failure (group C). Cardio-thoracic ratio, serum albumin and Ca correlated with QTc in group A, but not in B or C. A single HD session in group A failed to shorten QTc, despite a significant increase in serum Ca++. Autonomic dysfunction did not appear to be a major determinant of QT prolongation, since QTc was not different between diabetics and non-diabetics in group A and in chronic HD patients (group D). In group D, QTc did not correlate with SV1 + RV5 on ECG or left ventricular wall thickness (LVWT) on echocardiography. In another group of chronic HD patients (group E), there was no significant correlation between QTc and the parameters of left ventricular mass, plasma brain natriuretic peptide (BNP). However, in the patients subjected to repeated echocardiography in group D, QTc and LVWT changed in parallel. In a retrospective analysis of QTc in group D, QTc was maximally prolonged at the time of starting HD therapy, and gradually improved in the following 1-5 years in both diabetics and non-diabetics. In contrast, chronic CAPD patients (group F) revealed no improvement of QTc. Thus, uremic QT prolongation cannot be explained simply by any of the previously assumed factors, but appears to be affected by multiple factors, which are partially correctable by chronic HD therapy.

Functional MR imaging with venography for neurosurgical identification of the central sulcus

We evaluated the applicability of functional MR imaging overlaid onto brain images superimposed venography for neurosurgical identification of the central sulcus. In 20 volunteers and 12 patients with brain tumors located around the sensorimotor cortex, gradient echo and large flip angle functional MR image was performed to allow visualization of flow effect and susceptibility related changes in relative large vein by motor hand task. Functional MR image acquired was overlaid on 3D anatomical image with 3D venography. Based on the 3D mapping, intra-operative cortical somatosensory evoked potentials (SEPs) were recorded. The significant activation area obtained from functional MR imaging was projected on an ascending cortical vein in 16 volunteers (80%) and 10 patients (83%). Comparing the anatomical activation map with visual inspection of the exposed cortical surface made it easy to identify the activation area during surgery. The cortical veins in 9 of 10 were validated as a central vein by intra-operative cortical recording of SEPs. Combination of functional MR imaging overlaid onto 3D anatomical image with venography and intra-operative SEPs permitted rapid and accurate localization of the central sulcus during surgery.

AVP inhibits LPS- and IL-1beta-stimulated NO and cGMP via V1 receptor in cultured rat mesangial cells

The present study examined how arginine vasopressin (AVP) affects nitric oxide (NO) metabolism in cultured rat glomerular mesangial cells (GMC). GMC were incubated with test agents and nitrite, and intracellular cGMP content, inducible nitric oxide synthase (iNOS) mRNA, and iNOS protein were analyzed by the Griess method, enzyme immunoassay, and Northern and Western blotting, respectively. AVP inhibited lipopolysaccharide (LPS)- and interleukin-1beta (IL-1beta)-induced nitrite production in a dose- and time-dependent manner, with concomitant changes in cGMP content, iNOS mRNA, and iNOS protein. This inhibition by AVP was reversed by V1- but not by oxytocin-receptor antagonist. Inhibition by AVP was also reproduced on LPS and interferon-gamma (IFN-gamma). Protein kinase C (PKC) inhibitors reversed AVP inhibition, whereas PKC activator inhibited nitrite production. Although dexamethasone and pyrrolidinedithiocarbamate (PDTC), inhibitors of nuclear factor-kappaB, inhibited nitrite production, further inhibition by AVP was not observed. AVP did not show further inhibition of nitrite production with actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of protein synthesis. In conclusion, AVP inhibits LPS- and IL-1beta-induced NO production through a V1 receptor. The inhibitory action of AVP involves both the activation of PKC and the transcription of iNOS mRNA in cultured rat GMC.

Human recombinant erythropoietin inhibits interleukin-1beta-stimulated nitric oxide and cyclic guanosine monophosphate production in cultured rat vascular smooth-muscle cells

BACKGROUND

Recently rat vascular smooth-muscle cells (VSMC) have been shown to possess Epo receptor, and respond to various cytokines for producing nitric oxide (NO). In the present study we examined the effect of pharmacological dose of human recombinant erythropoietin (rHuEpo) on the IL-1beta-induced NO and cGMP production as well as inducible nitric oxide synthase (iNOS) in cultured rat VSMC.

METHODS

Nitrite, a stable metabolite of NO, and intracellular cGMP contents were assayed by Griess method and enzyme immunoassay. iNOS mRNA expression was analysed by Northern blotting.

RESULTS

RHuEpo inhibited IL-1beta-induced nitrite production in a dose- and time-dependent manner with concomitant changes of intracellular cGMP contents. On the other hand, rHuEpo did not inhibit atrial natriuretic peptide- (ANP) or sodium nitroprusside (SNP)-induced nitrite and cGMP production at all. While rHuEpo inhibited IL-1beta-induced iNOS mRNA expression, rHuEpo vehicle did not affect IL-1beta-induced iNOS mRNA expression.

CONCLUSIONS

It is suggested that a pharmacological dose of rHuEpo inhibits IL-1beta-induced NO and cGMP production as well as iNOS mRNA expression, presumably via the Epo receptor.

Incubation of OKP cells in low-K+ media increases NHE3 activity after early decrease in intracellular pH

Chronic hypokalemia increases the activity of proximal tubule apical membrane Na+/H+ antiporter NHE3. The present study examined the effect of the incubation of OKP cells (an opossum kidney, clone P cell line) in control medium (K+ concn ([K+]) = 5.4 mM) or low-K+ medium ([K+] = 2.7 mM) on NHE3. The activity of an ethylisopropyl amiloride-resistant Na+/H+ antiporter, whose characteristics were consistent with those of NHE3, was increased in low-K+ cells beginning at 8 h. NHE3 mRNA and NHE3 protein abundance were increased 2.2-fold and 62%, respectively, at 24 h but not at 8 h. After incubation in low-K+ medium, intracellular pH (pHi) decreased by 0.27 pH units (maximum at 27 min) and then recovered to the control level. Intracellular acidosis induced by 5 mM sodium propionate increased Na+/H+ antiporter activity at 8 and 24 h. Herbimycin A, a tyrosine kinase inhibitor, blocked low-K+- and sodium propionate-induced activation of the Na+/H+ antiporter at 8 and 24 h. Our results demonstrate that low-K+ medium causes an early decrease in pHi, which leads to an increase in NHE3 activity via a tyrosine kinase pathway.

Growth inhibition of leukemic cells by (-)-epigallocatechin gallate, the main constituent of green tea

In this report, we presented the results that EGCG, the main constituent of the polyphenols present in Japanese green tea inhibited growth of leukemic cell lines of both human and mice. The proliferation of human leukemic cell lines and mouse NFS60 cell line was inhibited by EGCG. Sensitivity of each line to EGCG was different, and more than 50% of DNA synthesis was reduced in all the cell lines in the presence of 50 microM EGCG. On the other hand, normal hematopoietic progenitor cells retained their natural function of supplying mature cells of various lineages in the presence of less than 10 microM EGCG in vitro. Even in the presence of 100 microM EGCG, half the colonies containing all the lineages of cells were developed. All the dead cells of each line showed characteristics of apoptosis, which might be due to inhibition by EGCG of growth factors' signaling. Besides anticarcinogenic activity, EGCG is expected to have a new function for leukemia therapy without side effects.

Dispersion of signal-averaged P wave duration on precordial body surface in patients with paroxysmal atrial fibrillation

AIMS

This study sought to investigate whether the spatial dispersion of signal-averaged P wave duration would be increased in patients with paroxysmal atrial fibrillation, by use of precordial mapping of the P wave signal-averaged ECG.

METHODS AND RESULTS

The P wave signal-averaged ECG was recorded by the P wave-triggering method from 16 precordial leads in 55 patients with paroxysmal atrial fibrillation and 57 control subjects. As an index of the dispersion of signal-averaged P wave duration, we obtained the difference between the maximum and minimum in 16 recording sites. The dispersion was significantly greater in the patients with paroxysmal atrial fibrillation than the controls (26.6 +/- 9.5 vs 14.8 +/- 6.7 ms, P<0.0001). In 25 patients with symptomatic attacks of paroxysmal atrial fibrillation, the signal-averaged ECG was repeated 1 h after a single dose of orally administered pilsicainide, a new class Ic drug. These patients were prospectively followed-up for 10 +/- 11 months with pilsicainide. The rate of freedom from recurrence of paroxysmal atrial fibrillation attacks was significantly (P<0.0001) higher in patients with whom dispersion was decreased by the single dose (54%[7/13]) than in those in whom dispersion increased (8%[1/12]).

CONCLUSION

Increased dispersion of signal-averaged P wave duration would play an important role in generating paroxysmal atrial fibrillation and would be useful in the prediction of drug efficacy to evaluate the change in dispersion by a single administration of pilsicainide.

Lipid A directly inhibits IL-4 production by murine Th2 cells but does not inhibit IFN-gamma production by Th1 cells

Lipopolysaccharide (LPS) is known to be an immunopotentiator but its effect on cytokine production by Th1 and Th2 cells is unknown. We found that high amounts of LPS, its lipid A moiety, and a lipid A analog all induced a decrease in IL-4 production and an increase in IFN-gamma production when given to keyhole limpet hemocyanin (KLH)-restimulated lymph node cells prepared from KLH-primed mice. Lipid A was similarly found to inhibit IL-4 production by purified CD4+ T cells and Th2 clones activated with immobilized anti-CD3epsilon and anti-CD28 antibodies, suggesting that the inhibition is not indirectly mediated through effects on antigen-presenting cells. No inhibitory effect of lipid A was observed on IFN-gamma production by a Th1 clone. Production of both IL-4 by the Th2 clones and IFN-gamma by the Th1 clone were inhibited by the immunosuppressive agent cyclosporin A. These findings indicate that lipid A can directly inhibit IL-4 production by CD4+ T cells without inhibiting the production of IFN-gamma. Lipid A may therefore become a useful tool to study the intracellular events that differentiate Th1 and Th2 cells.

Treatment with steroids and double filtration plasmapheresis for a case of anti-GQ1b antibody-positive Bickerstaff's encephalitis

The treatment of Bickerstaff's brainstem encephalitis (BBE) is still controversial. We report a case of BBE with positive anti-GQ1b antibody. The patient was successfully treated with steroids and double filtration plasmapheresis.

Human herpesvirus 6 latently infects mononuclear cells but not liver tissue

AIM

To investigate whether human herpesvirus 6 (HHV-6) can cause latent infection of liver tissue.

METHODS

Peripheral blood and liver tissue were collected from 25 living related liver transplant recipients at the time of transplantation. An avidin-biotin complex peroxidase method was used to identify HHV-6 antigen in the liver tissue. A nested polymerase chain reaction (PCR) was used to detect HHV-6 DNA in the liver tissue and mononuclear cells. Variant of HHV-6 was determined by the presence of the Hind III site in a second PCR product.

RESULTS

Immunohistochemical analysis for HHV-6 antigen was negative in all the liver specimens. HHV-6 DNA was not detected in liver tissue. Virus DNA was detected in peripheral blood mononuclear cells in nine of 25 recipients. All nine HHV-6 identified in the mononuclear cells were variant B.

CONCLUSIONS

HHV-6 variant B latently infects mononuclear cells but not liver tissue.

Basolateral Na+ pump modulates apical Na+ and K+ conductances in rabbit cortical collecting ducts

Previous studies indicated that an acute elevation of peritubular K+ enhances K+ secretion and Na+ reabsorption in the isolated perfused cortical collecting duct (CCD) from rabbit kidneys [S. Muto, G. Giebisch, and S. Sansom. Am. J. Physiol. 255 (Renal Fluid Electrolyte Physiol. 24): F108-F114, 1988]. To determine the underlying cellular mechanisms, we used microelectrode techniques to assess the membrane properties of collecting duct cells in isolated perfused CCDs of control and desoxycorticosterone acetate (DOCA)-treated rabbits following acute stimulation of the basolateral Na+-K+ pump by rapidly increasing the bath solution from 2.5 to 8.5 mM K+. This induced in both groups of tubules, first, a short-lasting hyperpolarization and, second, a sustained phase of depolarization of transepithelial, basolateral, and apical membrane voltages. Whereas the transepithelial conductance (GT) and fractional apical membrane resistance (fRA) remained unchanged during the initial phase of hyperpolarization, during the depolarization, GT increased and fRA decreased. Perfusion of the lumen with solutions containing either amiloride or Ba2+ attenuated the high K+-induced apical electrical changes, and basolateral strophanthidin abolished both apical and basolateral electrical responses during elevation of K+ in the bath. From these results we conclude the following: 1) acute elevation of basolateral K+ activates the basolateral Na+-K+ pump, which secondarily elevates the apical Na+ and K+ conductances; 2) DOCA pretreatment increases the basolateral K+ conductance and augments the response to the rise of K+ of both basolateral Na+-K+ pump activity and apical cation conductances.