Cerebrospinal fluid levels of amyloid beta-peptide1-42, but not tau have positive correlation with brain glucose metabolism in humans

To address the question of whether assay for cerebrospinal fluid (CSF) levels of amyloid beta-peptide 1-42 (A(beta)1-42) and tau allow us to monitor the neurodegenerative processes that lead to a progressive and massive death of neurons in Alzheimer's disease (AD) and non-AD patients, cerebral glucose metabolism using 2-[18F] fluoro-2-deoxy-glucose was quantified by positron emission tomography in fifteen AD patients and nine non-AD patients with defined levels of CSF-A(beta)1-42 and CSF-tau. The CSF-A(beta)1-42 levels, but not the CSF-tau levels, in both AD and non-AD patients consistently and significantly correlated with global and, in particular, temporal lobe glucose metabolism. Results from our study suggest that the CSF-A(beta)1-42 levels may reflect residual brain function and help monitoring progression of dementing disorders.

Avirulent Avian influenza virus as a vaccine strain against a potential human pandemic

In the influenza H5N1 virus incident in Hong Kong in 1997, viruses that are closely related to H5N1 viruses initially isolated in a severe outbreak of avian influenza in chickens were isolated from humans, signaling the possibility of an incipient pandemic. However, it was not possible to prepare a vaccine against the virus in the conventional embryonated egg system because of the lethality of the virus for chicken embryos and the high level of biosafety therefore required for vaccine production. Alternative approaches, including an avirulent H5N4 virus isolated from a migratory duck as a surrogate virus, H5N1 virus as a reassortant with avian virus H3N1 and an avirulent recombinant H5N1 virus generated by reverse genetics, have been explored. All vaccines were formalin inactivated. Intraperitoneal immunization of mice with each of vaccines elicited the production of hemagglutination-inhibiting and virus-neutralizing antibodies, while intranasal vaccination without adjuvant induced both mucosal and systemic antibody responses that protected the mice from lethal H5N1 virus challenge. Surveillance of birds and animals, particularly aquatic birds, for viruses to provide vaccine strains, especially surrogate viruses, for a future pandemic is stressed.

Determinants of organ tropism of sendai virus

Wild-type Sendai virus is exclusively pneumotropic in mice. Protease activation mutants, ts-f1 and F1-R, were isolated from persistently infected tissue culture cells. Additional mutants were isolated from wild-type Sendai virus with phenotypes similar to the pantropic mutant, F1-R. The genome of the mutants was sequenced and mutations were revealed in several proteins encoded by the genes. Three of the six mutations in the fusion (F) proteins were considered prime candidates for the determinant of pantropism. Characterization of the mutants led to the finding that the exchange (Ser to Pro) residue 115 next to the cleavage site of the F protein was the primary determinant that resulted in the enhanced cleavability of the F protein. Another important finding was bipolar budding of F1-R in polarized epithelial cells and mouse bronchial epithelium. This has been attributed to two mutations in the matrix (M) protein, at residues 128 (Asp to Gly) and 210 (Ile to Thr). Thus the determinants of pantropism of F1-R are protease activation of the F protein and bipolar budding attributed to the mutated M protein and enhanced disruption of microtubules.

[A report on clinical PET activities in Germany]

Clinical diagnostic procedure using positron emission tomography (PET) requires high costs. To promote clinical use of PET, sociomedical evaluation is necessary. In this paper, sociomedical situations concerning clinical use of PET in Germany is reported. Some comparisons are made between Japan and this country putting emphases on several points such as 1) number of cyclotron and PET facilities, 2) social restriction to transportation of radioisotopes, 3) activities of satellite PET facilities, and 4) clinical indications for PET studies. Number of cyclotron was larger in Japan (29) than in Germany (17), but number of PET facilities was larger in Germany (47) than in Japan (29). The reason seems that in Germany transportation and buying of radioisotopes is less restricted. Hence, more than half of PET facilities in Germany are "satellite facilities" which do not have their own cyclotrons. Radioisotope distribution seems to serve as a backbone of "satellite concept." Additionally in Germany, list of clinical indications for PET study is almost completed and now is widely in applied to most cases. To promote clinical use of PET in Japan, the German system might serve as an important socioeconomic model in Europe instead of the United States.

Hypometabolism in the limbic system of cancer patients observed by positron emission tomography

Brain images obtained by a positron emission tomography with 18F-fluorodeoxyglucose from 19 pretreatment cancer patients with variable cancers except brain cancers were compared with those from 17 inpatients with benign diseases. Relative reduction in regional cerebral metabolism of glucose was found mainly in the limbic structures including the bilateral orbitofrontal cortex, lateral frontal cortex, cingulate gyrus, thalamus, hippocampus and parahippocampal gyrus, insulae, and basal ganglia. The regional metabolism tended to be low in the patients who had severe pains which required opiates and morphines, and tended to be preserved in the patients who were already disclosed of their malignancy based on previous studies such as biopsy. Our findings would support that psychological deficits in cancer patients are associated with abnormalities in regional brain metabolism in the limbic system.

Cerebrospinal fluid tau protein levels in demented and nondemented alcoholics

The tau protein levels in cerebrospinal fluid (CSF-tau) were examined in 27 patients with alcohol dependence (20 demented and 7 nondemented), 36 age and dementia severity-matched patients with Alzheimer's disease (AD), and 23 age-matched normal control subjects. The CSF-tau levels in the demented alcoholic group (alcohol-induced organic brain disorders, 25.4 +/- 10.2 pg/ml) was significantly lower (p < 0.0001) than that in the AD group (96.1 +/- 53.3 pg/ml), but not significantly different from that in the nondemented alcoholics (18.1 +/- 10.2 pg/ml) or the controls (19.2 +/- 12.9 pg/ml). Using a 44.9 pg/ml as a cut-off value (mean + 2 SD of the normal control group), only one patient with alcohol-induced organic brain disorders exceeded the value, whereas 3 of 36 of the AD group showed CSF-tau levels less than this level. These findings suggest that alcohol-induced organic brain disorders are a group of dementias that are characterized by normal CSF-tau levels, and that the CSF examination for tau in combination with other clinical findings may help in differentiating alcohol-induced organic brain disorders from AD.

Pharmacologic profile of TS-941, a new benzodiazepine derivative cholecystokinin-receptor antagonist, in in vitro isolated rat pancreatic acini

We investigated the pharmacologic characteristics of a newly developed benzodiazepine derivative (S)-(-)-N-[2,3-dihydro-2-oxo-5-phenyl-1-[(1H-tetrazol-5-yl)methyl] -1H-1,4-benzodiazepine-3-yl]-2-indolecarboxamide (TS-941), a cholecystokinin type A (CCK-A)-receptor antagonist, in the isolated rat pancreatic acini and compared with those of well-known CCK-A-receptor antagonists, devazepide and loxiglumide. TS-941 inhibited CCK-8-stimulated amylase release concentration dependently, as did devazepide and loxiglumide, with a half-maximal inhibition (IC50) at 78.6 +/- 10.3 nM. TS-941 was approximately 23 times less potent than devazepide (IC50, 3.4 +/- 0.3 nM), but was 50 times more potent than loxiglumide (IC50, 3,966 +/- 544 nM) in inhibiting 100 pM CCK-8-stimulated amylase release from rat pancreatic acini. TS-941 had a fivefold lower selectivity than devazepide for pancreatic CCK (CCK-A) over brain CCK (CCK-B) receptors but fourfold greater than loxiglumide when IC50 values for inhibition of [125I]CCK-8 binding in isolated acini and cerebral cortex were compared. The antagonism produced by TS-941 was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. TS-941 caused a parallel rightward shift of the entire dose-response curve for CCK-8-stimulated amylase release without altering the maximal increase, as did devazepide and loxiglumide. TS-941, whether added at the beginning or 20 min after the CCK-8 stimulation, inhibited amylase release. TS-941 caused a concentration-dependent residual inhibition of the action of CCK-8. The acini, once incubated with a high concentration of TS-941 (10 microM; 127 times IC50) for 30 min, was 10-fold less sensitive to CCK-8 than the acini preincubated without TS-941, whereas the sensitivity and the responsiveness to CCK-8 stimulation of those incubated with a low concentration of TS-941 (1.0 microM) were similar to the control acini. These results indicate that TS-941 is a potent, competitive, and selective CCK-A receptor antagonist for the pancreas.

Determinants of pantropism of the F1-R mutant of Sendai virus: specific mutations involved are in the F and M genes

Mutations in the fusion, F, protein of Sendai virus resulting in increased cleavability by ubiquitous host protease(s), and mutations in the matrix, M, protein resulting in bipolar budding, are both important determinants for the systemic infection in mice caused by the protease activating pantropic mutant, F1-R. Several mutants of Sendai virus (BY, BF, and KD-M) with phenotypes of bipolar budding and/or increased cleavability of F protein were isolated. Genomic RNA sequence analysis of the F and M genes of the mutants revealed that several deduced amino acids in the F and M proteins were different from those of F1-R, T-5 (a revertant of F1-R), and wild-type viruses. The BF and KD-M mutants that budded bipolarly and were also activated by ubiquitous proteases were examined for replication in tissue culture cells and in mice. All of the mutants exhibited multiple-step replication in MDCK, MDBK, and LLC-MK2 cells without trypsin, but formed plaques only in MDCK cells. One of the mutants, designated KD-52M, was similar to F1-R in that it formed plaques in all three cell lines without addition of exogenous protease. However, none of the mutants viruses, including KD-52M, caused a systemic infection in mice. The mutated M protein of F1-R enhances the disruption of microtubles. However, none of the mutants with a bipolar budding phenotype (BY, BF, and KD-M), disrupted the microtubules to the same extent as F1-R. All of these mutants had mutations in the M protein that were different from those found in F1-R. Taken together, these results suggest that mutations at Ser115 to Pro in the F protein and at Asp 128 to Gly and Ile210 to Thr in the M protein of F1-R are the mutations specifically required for the systemic infection caused by F1-R.

18F-FDG PET imaging of muscle activity in runners

PET with three-dimensional data acquisition using 18F-fluorodeoxyglucose (FDG) was applied to evaluate skeletal muscle activity in runners.

METHODS

Seven healthy adult male volunteers were studied. They ran for a total of 35 min, 15 min before and 20 min after intravenous injection of FDG. Another 7 adult male control subjects were also examined at rest. Images obtained through a set of whole-body PET scans were analyzed. Regions of interest (ROIs) were manually drawn on images of muscles of both thighs, legs and feet, and the standardized uptake ratio (SUR) and total radioactivity distribution (TRD) for each region were calculated.

RESULTS

The work load was below the anaerobic threshold. SUR of foot, leg and thigh were low at rest but during running increased 5.19, 4.30 and 1.74 times, respectively. The SUR of posterior-to- anterior compartment of the leg was 1.1+/-0.1 at rest and 1.6+/-0.5 (P < 0.01) during running. The laterality index of both SUR and TRD changed significantly only in the foot of the dominant side during running. TRD of the leg, less than half that of the thigh at rest, became equivalent to that of the thigh during running. TRD of the foot did not change significantly.

CONCLUSION

Sole muscles showed highest metabolic activation per unit volume during running, which was higher in the dominant side. Comparison of whole muscle activity during running indicated the highest metabolic activation was in the posterior compartment of the leg, whereas thigh muscles showed relatively little changes during running. Our data indicate that whole-body FDG PET, especially three-dimensional data acquisition, is a useful tool for the investigation of muscular activity during exercise.

Defects of cholecystokinin (CCK)-A receptor gene expression and CCK-A receptor-mediated biological functions in Otsuka Long-Evans Tokushima Fatty (OLETF) rats

Recent studies in genetically obese and diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats suggest defects of cholecystokinin (CCK)-A receptor gene expression and CCK-A receptor-mediated biological functions such as pancreatic juice, protein, and gastric acid secretion. The present studies were undertaken to further examine CCK-A receptor gene expression and CCK-A receptor-mediated biological functions in the pancreas, stomach, and brain of OLETF rats. Expression of the CCK-A receptor gene could not be detected in the stomach, pancreas and brain by the reverse-transcription polymerase chain reaction (RT-PCR) method and Southern blotting of the PCR products. Southern blot analysis of genomic DNA from OLETF and control Long-Evans Tokushima Otsuka (LETO) rats with CCK-A receptor fragment as a probe revealed different restriction bands. Expression of the CCK-B receptor gene was observed in the stomach, pancreas, and brain in both OLETF and LETO rats by the RT-PCR method, with expression of the CCK-B receptor gene markedly enhanced in OLETF rats compared with that in LETO rats. Consistent with the defect of CCK-A receptor gene expression, CCK-A receptor-mediated biological functions were not observed in these organs. Perfused exocrine and endocrine pancreas of OLETF rats were insensitive to CCK stimulation but not to carbamylcholine stimulation. Basal gastric acid and pepsinogen secretions in OLETF rats were higher than in LETO rats. OLETF rats showed a significantly higher average daily food intake, gained body weight faster, and were heavier than LETO rats. The present study confirmed that OLETF rats have CCK-A receptor gene anomalies and demonstrated deficient CCK-A receptor-mediated biological function in the pancreas, stomach, and brain.

A new heparin-bonded dense membrane lung combined with minimal systemic heparinization prolonged extracorporeal lung assist in goats

Heparin was covalently bonded to a new hollow-fiber dense membrane artificial lung and extracorporeal circuit using a silane coupling agent and polyethyleneimine. This study investigated whether prolonged, venoarterial bypass extracorporeal lung assist (V-A bypass ECLA) could be sustained in a goat by the combination of the new membrane lung and minimal systemic heparinization. We maintained ECLA with the hollow-fiber lungs (surface area, 0.8 m2) and circuits by titrating the activated clotting time (ACT) to below 150 s with minimal systemic heparinization in 5 goats. The outcome was assessed from the function of the artificial lung via macro and microscopic examinations after the experiments and the incidence of systemic complications. The 5 goats were maintained on ECLA for 6 to 27 days. The bypass flow rate, blood gases at the return and drainage sites, platelet counts, and platelet aggregation activity were well maintained. Although the hemoglobin concentration, hematocrit, and plasma protein at the start of the ECLA were significantly lower than the pre-ECLA values due to hemodilution, the values remained stable during ECLA. A cerebral infarction occurred in 1 goat. However, in the other 4 goats, no complications such as bleeding, thrombosis, or plasma leakage from the artificial lung were observed. Although several thrombi were observed in the stagnant area of the artificial lung, these local thrombi did not cause the function of the artificial lung to deteriorate. We found that this new type of highly biocompatible, dense membrane artificial lung, when combined with minimal systemic heparinization, prolonged ECLA without the deterioration of the artificial lung function and was suitable for prolonged ECLA.

Interaction of second and third domains of Japanese quail ovomucoid with ten mammalian trypsins

Second and third domains were prepared from Japanese quail ovomucoid and association equilibrium constants, Kas, were measured at 25 degreesC and pH 8 for these domains with trypsins from ten mammalian species: cat, cow, dog, guinea pig, hog, horse, man, rabbit, rat, and sheep. The values ranged from 108 M-1 to 1010 M-1 for the second domain-trypsin associations and from 106 M-1 to 108 M-1 for the third domain-trypsin associations. Changes in Ka values for the interactions between the trypsins and each domain are attributed to slight changes in surface conformation caused by the residue changes in the inhibitor-binding region other than the S1 pocket of the trypsin species. The representative of such residue changes is assumed to be the one observed at residue 217 of trypsin molecule. Concerning each trypsin, the Ka value with the second domain was always higher than that with the third domain. However, the ratios between the two equilibrium constants varied from 3 to 60 depending upon trypsin species. This means that amino acid changes in enzyme-contact residues other than the P1 site of the Kazal-type inhibitor can make it possible to recognize even a slight difference in inhibitor-binding surface among the enzymes with the same S1 pocket and highly similar overall three-dimensional structure.

Apoptosis in the lens anlage of the heritable lens aplastic mouse (lap mouse)

Adult homozygous lap mice show various eye abnormalities, such as aphakia, retinal disorganization, and dysplasia of the cornea and anterior chamber. In the fetal eye of a homozygous lap mouse, the lens placode seems to develop normally. However, the lens vesicle progresses abnormally to form a mass of cells without a cavity, and the mass vanishes soon afterward. We examined cell death in the lens anlage of this mutant. The lens anlagen of homozygous lap and normal mice from days 10 to 12 of gestation were observed by light microscopy after DNA end-labeling by immunohistochemistry and by transmission electron microscopy. By light microscopy, a slight frequency of cell death was detected in the lens anlage encircling the surface ectoderm and in the anlage or in the anlage of both homozygous lap mice and normal mice at day 10 of gestation. Cell death was seen in the lens anlage encircling the surface ectoderm in the normal mouse and sporadically in the anlage of the homozygous lap mouse at day 10.5 of gestation. Cell death was visible at the area of the lens vesicle attached to the surface ectoderm and encircling the surrounding surface ectoderm in the normal mouse, and in the lens anlage encircling the surface ectoderm and the apex areas of the lens anlage in the homozygous lap mouse at day 11 of gestation. At day 12 of gestation, almost no cell death was observed in the lens anlage of the normal mouse. However, extensive areas of cell death were still seen in the lens anlage at its apex, at the inner region, and encircling the surface ectoderm in the homozygous lap mouse. Electron microscopic observation showed that the dead cells observed in the lens anlagen by light microscopy in normal and lap mice are the result of apoptosis. In lap mice, cells with cytoplasmic condensation were observed mainly at days 10 and 10.5 of gestation. Many apoptotic bodies which had been phagocytosed by adjacent cells were seen predominantly at day 11 of gestation. At day 12 of gestation, apoptotic bodies phagocytosed by adjacent cells, which were seen at day 11, were still predominant, but there were more apoptotic bodies per cell and more digested apoptotic bodies than at day 11. These results indicate that cell death, resulting from apoptosis is involved in the disappearance of the lens anlage of lap mice.

Nucleoprotein gene analysis of fixed and street rabies virus variants using RT-PCR

A simple and rapid single-step reverse transcriptase-polymerase chain reaction (RT-PCR) was used to investigate the nucleoprotein (N) gene of 11 rabies viruses. A conserved set of RT-PCR primers was designed to amplify the most variable region in the N gene. N gene regions were amplified from 6 fixed laboratory viruses, 4 street viruses from dogs in Thailand, and a horse in Zambia. Sequences of the amplified products, together with the database of 91 additional sequences, were analyzed by using PILEUP program of the GCG package. The rabies viruses grouped into at least 9 distinct clusters by < 90% nucleotide similarity of the N gene region: I (4 isolates, USA), II (2 isolates, South America), III (3 isolates, Africa), IV (52 strains, Europe, Middle East, Africa and South America), V (16 isolates, North America and Arctic), VI (17 isolates, Africa), VII (1 isolate, Africa), VIII (6 isolates, Thailand and Malaysia) and IX (1 isolate, Sri Lanka). A unique group of rabies viruses from Thailand and clusters of isolates corresponding to their geographic origin also were determined. The simple and rapid single-step RT-PCR proved to be useful for identifying rabies viruses, and for grouping the viruses into clades by sequence analysis.

High oxygen delivery and extraction by perfluorocarbon-primed extracorporeal membrane oxygenation do not prevent anaerobic metabolism in rabbits

PURPOSE

This study was designed to evaluate the advantage of perfluorocarbon (PFC) emulsion priming for venoarterial extracorporeal membrane oxygenation (ECMO) by comparison with hydroxyethyl starch (HES) solution in rabbits (2.8 to 3.9 kg).

RESULTS

ECMO initiation was accompanied by a profound decrease in hematocrit (from 40.1% to 14.9%) in both groups. The arterial and the right atrial oxygen contents in the PFC group (n = 4; 38.5 and 11.5 mL/dL) were greater than in the HES group (n = 5; 7.0 and 5.1 mL/dL). Right atrial oxygen tension in the PFC group increased at the beginning of ECMO (from 38.4 to 51.2 mm Hg; P = .031) and remained higher than in the HES group for 60 minutes. These results indicate that oxygen supply and extraction in the PFC group were much greater than in the HES group. However, plasma lactate increased progressively during the 120-minute ECMO procedure in both groups (from 1.8 to 14.5 in the HES group, and from 2.3 to 12.2 in the PFC group).

CONCLUSION

Perfluorocarbon priming for ECMO, although providing high oxygen delivery and extraction, does not prevent anaerobic metabolism.

HIV-1 Nef binding protein expressed on the surface of murine blood cells

The Nef protein of HIV-1 binds to and induces apoptotic cytolysis of a broad spectrum of uninfected blood cells of humans and mice independently of CD95 (Fas). A 24-kDa glycoprotein responsible for Nef binding and the Nef-induced apoptosis has been identified on the surface of human CD4+ T cells. Using mouse monoclonal antibodies (mAbs) against the human Nef-binding protein and flow cytometry, we analyzed the expression of a corresponding protein on murine cells. The mAbs were shown to bind to the surface of various murine cell lines including T and B lymphocytes and macrophages, in a fashion similar to the binding by soluble Nef protein. The mAbs competed with the Nef protein in binding to the cell surfaces. Immunoprecipitation of cell membranes revealed a 25-kDa protein recognized by the mAbs. Treatment of the soluble Nef protein with anti-Nef (C terminus) mAb, but not anti-Nef (N terminus) mAb, deprived the Nef of the cell binding activity, indicating that binding site is located in the C-terminal domain. Cross-linking of the cell-bound mAbs with secondary antibodies induced apoptotic cytolysis, which occurred independently of CD95 (Fas). On the other hand, neither the mAbs nor the soluble Nef protein reacted with primary lymphocytes in a resting stage obtained from lymph nodes, thymus and spleen of 5-week-old mice. However, some of the cells, predominantly comprising CD4+ T cells, became positive for the both reactions after mitogenic stimulation with phytohemagglutinin, concanavalin A or lipopolysaccharide of Escherichia coli. These results suggest that the 25-kDa protein on murine cell surfaces corresponds to the human Nef binding protein and is responsible for the Nef-induced apoptosis, and that its expression on the cell surface depends on cellular activation.

Inhibition of HIV-1 Nef-induced apoptosis of uninfected human blood cells by serine/threonine protein kinase inhibitors, fasudil hydrochloride and M3

The Nef protein of HIV-1 binds to and induces apoptotic cytolysis of uninfected but activated human peripheral blood mononuclear cells (PBMC) and various cell line cells derived from CD4+ T, CD8+ T and B lymphocytes, macrophages, and neutrophils. The Nef-induced apoptosis also occurs with blood cells not expressing CD95 (Fas). The Nef-induced apoptosis as well as Fas-mediated apoptosis was inhibited by acetyl-Try-Val-Ala-Asp-CHO, an IL-1beta converting enzyme (ICE) inhibitor. On the other hand, serine/threonine protein kinase (PK) inhibitors, H-7, fasudil hydrochloride and M3, inhibited the Nef-induced apoptosis, and not the Fas-mediated one, without affecting the cell-binding activity of Nef and Nef-binding capacity of the activated cells. Preincubation of the cells with the drugs before being bound by Nef was required for the inhibition of apoptosis. These results suggest that the PK inhibitors specifically act on a cellular protein involved in the upper stream of signal transduction pathway of the Nef-induced apoptosis, which is different from the Fas-mediated pathway but meets it upstream of ICE. In addition, the drugs suppressed the cellular activation-associated cell surface expression of a putative Nef-binding protein in PBMC, although they had no influence on its expression in cell line cells. These findings suggest the feasibility of clinical use of the PK inhibitors to prevent the development of AIDS by inhibiting the Nef-induced apoptosis of uninfected blood cells.

Basal intracellular free Mg2+ concentration in smooth muscle cells of guinea pig tenia cecum: intracellular calibration of the fluorescent indicator furaptra

Longitudinal muscle strips dissected from tenia cecum of guinea pig were loaded with the Mg2+ indicator, furaptra, and the relation between the fluorescent ratio signal (R) and cytoplasmic free Mg2+ concentration ([Mg2+]i) was studied in smooth muscle cells at 25 degrees C. After the application of ionophores (4-bromo-A23187, monensin, and nigericin), a small immediate offset of R (deltaRjump) was followed by a slow change in R (deltaRslow), which reached a steady level within 2-5 h. The deltaRjump was independent of Mg2+ concentration in solution ([Mg2+]o), and was thought to be unrelated to the change in [Mg2+]i. The direction of the deltaRslow depended on [Mg2+]o with a reversal at approximately 1 mM [Mg2+]o. The intracellular calibration curve was constructed from the steady levels of deltaRslow, and the dissociation constant was 5.4 mM. With the intracellular calibration curve and correction for the deltaRjump, basal [Mg2+], was estimated to be 0.98 +/- 0.05 mM (mean +/- SE, n = 12). When the same calibration was applied to A7r5 cells and rat ventricular myocytes, estimates of basal [Mg2+]i of these cells were 0.74 +/- 0.02 mM (n = 33) and 1.13 +/- 0.06 mM (n = 9), respectively. These results suggest that the basal [Mg2+] level is approximately 1 mM at least in some types of smooth muscle cells, as generally found in striated muscles.

Determinants of organ tropism of Sendai virus

Wild-type Sendai virus is exclusively pneumotropic in mice. Protease activation mutants, ts-f1 and F1-R, were isolated from persistently infected tissue culture cells. Additional mutants were isolated from wild-type Sendai virus with phenotypes similar to the pantropic mutant, F1-R. The genome of the mutants was sequenced and mutations were revealed in several proteins encoded by the genes. Three of the six mutations in the fusion (F) proteins were considered prime candidates for the determinant of pantropism. Characterization of the mutants led to the finding that the exchange (Ser to Pro) residue 115 next to the cleavage site of the F protein was the primary determinant that resulted in the enhanced cleavability of the F protein. Another important finding was bipolar budding of F1-R in polarized epithelial cells and mouse bronchial epithelium. This has been attributed to two mutations in the matrix (M) protein, at residues 128 (Asp to Gly) and 210 (Ile to Thr). Thus, the determinants of pantropism of F1-R are protease activation of the F protein and biopolar budding attributed to the mutated M protein.

Na+ gradient-dependent Mg2+ transport in smooth muscle cells of guinea pig tenia cecum

Thin strips of guinea pig tenia cecum were loaded with the Mg2+ indicator furaptra, and the indicator fluorescence signals measured in Ca2+-free condition were converted to cytoplasmic-free Mg2+ concentration ([Mg2+]i). Lowering the extracellular Na+ concentration ([Na+]o) caused a reversible increase in [Mg2+]i, consistent with the inhibition of Na+ gradient-dependent extrusion of cellular Mg2+ (Na+-Mg2+ exchange). Curve-fitting analysis indicated that the relation between [Na+]o and the rate of rise in [Mg2+], had a Hill coefficient of approximately 3, a [Na+]o at the half-maximal rate of rise of approximately 30 mM, and a maximal rate of 0.16 +/- 0.01 microM/s (mean +/- SE, n = 6). Depolarization with 56 mM K+ shifted the curve slightly toward higher [Na+]o without significantly changing the maximal rate, suggesting that the Na+-Mg2+ exchange was inhibited by depolarization. The maximal rate would correspond to a flux of 0.15-0.4 pmol/cm2/s, if cytoplasmic Mg2+ buffering power (defined as the ratio of the changes in total Mg2+ and free Mg2+ concentrations) is assumed to be 2-5. Ouabain (1-5 microM) increased the intracellular Na+ concentration, as assessed with fluorescence of SBFI (sodium-binding benzofuran isophthalate, a Na+ indicator), and elevated [Mg2+]i. In ouabain-treated preparations, removal of extracellular Na+ rapidly increased [Mg2+]i, with an initial rate of rise roughly proportional to the degree of the Mg2+ load, and, probably, to the Na+ load caused by ouabain. The enhanced rate of rise in [Mg2+]i (up to approximately 1 microM/s) could be attributed to the Mg2+ influx as a result of the reversed Na+-Mg2+ exchange. Our results support the presence of a reversible and possibly electrogenic Na+-Mg2+ exchange in the smooth muscle cells of tenia cecum.