Search PubMed⌕ Search

Biomedical subjects

S Muto

Publications and source records attributed to S Muto.

At least 109 records · Page 6Linked to original sources
PubMed1994

Axial heterogeneity of potassium transport across hamster thick ascending limb of Henle's loop.

Functional significance of morphological heterogeneities along the thick ascending limb of Henle's loop of hamsters was explored by the in vitro microperfusion technique with special reference to K+ transport. The transmission electron microscopic study confirmed that there are two types of cells, with smooth surface (S-cell) and rough surface (R-cell), respectively, and that the former is abundant in the medullary thick ascending limb (MTAL), whereas the latter is in the cortical portion (CTAL). The electrophysiological study revealed that in both segments there are two cell populations, one having high basolateral and low apical membrane K+ conductances (HBC) and the other having low basolateral and high apical K+ conductances (LBC). Random cell puncture revealed that the ratios of HBC/LBC were 24/7 (77%/23%) in the MTAL and 7/22 (24%/76%) in the CTAL, suggesting that HBC corresponds to S-cell, whereas LBC corresponds to R-cell. Net K+ transport was determined in two segments by measuring K+ concentration in the collected and perfused fluid by ultramicroflame photometry. In all six tubules of MTAL, net K+ flux had a direction to reabsorption with a mean of 4.87 +/- 0.46 pmol.min-1.mm-1. In marked contrast, in all six tubules of CTAL, we observed K+ secretion with a mean of -3.81 +/- 0.49 pmol.min-1.mm-1. The transmural voltage was positive in both segments and was significantly higher in the CTAL (7.8 +/- 0.5 mV) than in the MTAL (2.5 +/- 0.2 mV). From these observations, we conclude that the S-cell corresponding to the HBC cell reabsorbs K+, whereas the R-cell corresponding to the LBC cell secrets K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Short-term effects of uninephrectomy on electrical properties of the cortical collecting duct from rabbit remnant kidneys.

Microelectrode techniques were used to assess the electrical properties of the collecting duct cell in the isolated perfused cortical collecting duct from remnant kidneys 3, 6, and 24 h after uninephrectomy (UNX); results were compared with those from sham-operated kidneys. Plasma aldosterone levels did not change during the time course after UNX. The lumen-negative transepithelial voltage was elevated significantly 3 h after UNX, and was increased further 24 h after UNX. The basolateral membrane voltage (VB) was elevated 6 h after UNX, and then was increased further at 24 h. Although the tight junction conductance and the fractional apical membrane resistance (fRA) were not altered at any time points after UNX, the apical membrane conductance as well as the transepithelial (GT) and basolateral membrane conductances increased 6 and 24 h after UNX. The changes in apical membrane voltage, GT, and fRA upon addition of luminal amiloride increased just 3 h after UNX, and then remained elevated at 6 and 24 h. The changes in apical membrane voltage and GT upon addition of luminal Ba2+, the changes in VB upon addition of bath ouabain, and the changes in VB, GT, and fRA upon raising bath K+ were not influenced 3 h after UNX, but increased at 6 and 24 h. At these latter periods after UNX, the transference number of Cl- of the basolateral membrane decreased significantly, whereas the transference number of K+ of the basolateral membrane increased significantly. Simultaneously, addition of Ba2+ to the bath caused the VB to hyperpolarize in parallel with decreases in GT and fRA. We conclude: (a) the initial effect of UNX (3 h) in the collecting duct cell is an increase in apical membrane Na+ conductance; (b) the delayed effects of UNX (6 and 24 h) are increases in apical membrane K+ conductance as well as basolateral membrane Na(+)-K+ pump activity and K+ conductance; (c) the hyperpolarization of VB at 6 and 24 h after UNX may result in the decrease of the ratio of the relative Cl- conductance to the relative K+ conductance of the basolateral membrane and also may increase passive K+ entry into the cell across the basolateral membrane; (d) these time-dependent electrical changes occur independently of plasma aldosterone levels.

Aldosterone↗
PubMed1994

Electrical properties of the rabbit cortical collecting duct from obstructed kidneys after unilateral ureteral obstruction. Effects of renal decapsulation.

Ureteral obstruction causes impaired salt wastage and K+ secretion in the distal nephron segments, including the cortical collecting duct (CCD). Recently, we demonstrated that conductances of Na+ and K+ in the apical membrane, as well as the electrogenic Na(+)-K+ pump activity and the relative K+ conductance in the basolateral membrane of the collecting duct cell, were inhibited in the obstructed kidney after unilateral ureteral obstruction (UUO). To examine whether the increased intrarenal pressure might be causally related to these abnormalities in the CCD, the effects of unilateral renal decapsulation, a maneuver that partially blocks the increase in renal pressure, were evaluated with microelectrode techniques in isolated CCDs from UUO and sham-operated (control) rabbits 24 h after operation. Renal decapsulation had no effects on barrier voltages and conductances in the CCD from control animals. The lumen-negative transepithelial (VT) and basolateral membrane (VB) voltages as well as the transepithelial (GT) and the apical membrane (GA) conductances were decreased in the CCD from UUO animals compared with control animals. Pretreatment of renal decapsulation partially corrected the decreases in VT, VB, GT, and GA seen in the CCD from UUO animals. The changes in apical membrane voltage and GT upon addition of luminal amiloride and Ba2+, and the changes in VB upon addition of bath ouabain, were also decreased in the CCD from UUO animals compared with control animals. Pretreatment of renal decapsulation also partially corrected the above abnormalities seen in UUO animals, whereas it had no effect in control animals. The transference numbers for Cl- (tCl) and K+ (tK) in the basolateral membrane were, respectively, increased and decreased in the CCD from UUO animals compared with control animals. Pretreatment of renal decapsulation also partially corrected the changes in tCl and tK seen in UUO animals, whereas it had no effect in control animals. We conclude that, in UUO animals, renal decapsulation partially corrects the inhibition of apical Na+ and K+ conductances as well as basolateral Na(+)-K+ pump activity and relative K+ conductance seen after UUO, whereas in control animals it has no effect. The increased renal pressure may partly contribute to the defects in Na+ and K+ transport in the CCD from obstructed kidneys. Renal decapsulation has protective effects on impaired Na+ and K+ transports in the CCD after ureteral obstruction.

Animals↗
PubMed1993

Structural analysis of periplasmic carbonic anhydrase 1 of Chlamydomonas reinhardtii.

Periplasmic carbonic anhydrase 1 of the unicellular green alga Chlamydomonas reinhardtii is a heterotetrameric glycoprotein consisting of two large subunits and two small subunits [Kamo, K., Shimogawara, K., Fukuzawa, H., Muto, S. & Miyachi, S. (1990) Eur. J. Biochem. 192, 557-562]. The cDNA sequence showed that the two subunits are cotranslated as a 377-amino-acid precursor polypeptide (41.6 kDa) consisting of an N-terminal 20-amino-acid signal peptide, a large subunit (35.6 kDa) and a small subunit (4.1 kDa) [Fukuzawa, H., Fujiwara, S., Yamamoto, Y., DionisioSese, M. L. & Miyachi, S. (1990) Proc. Natl Acad. Sci. USA 87, 4383-4387]. In the present study, amino-acid-sequence analysis of the carbonic anhydrase 1 was carried out to determine the sites of disulfide bonds and N-glycosylation and the C-terminal amino acid of the large subunit. Disulfide bonds were detected between Cys21 and Cys21, Cys61 and Cys264, Cys194 and Cys198, and Cys296 and Cys351 in the amino acid sequence deduced from the cDNA. Cys21 and Cys21 link two large subunits and Cys296 and Cys351 link a large subunit to a small subunit. Thus, the holoenzyme is constructed of two disulfide-bound large subunits, each of which joins to a small subunit by a disulfide bond. The C-terminal amino acid residue of the large subunit was determined as Ala305. This indicates that the peptide consisting of 35 amino acid residues between the large and the small subunit is deleted from the precursor during maturation, since the N-terminus of the small subunit is Ala341. Three potential N-glycosylation sites in the large subunit were all glycosylated.

Amino Acid Sequence↗
PubMed1993

CR3 (CD11b/CD18) expressed by cytotoxic T cells and natural killer cells is upregulated in a manner similar to neutrophil CR3 following stimulation with various activating agents.

CR3 (CD11b/CD18) functions both as an iC3b-receptor and as an adhesion molecule for cellular ligands such as ICAM-1. Although CR3 has been well characterized on phagocytic cells, much less is known about CR3 on lymphocytes. In this study, the expression of CR3 was examined on resting and stimulated B, T, and natural killer (NK) cells by three-color flow cytometry. Biotinylated anti-CR3 mAb and streptavidin-FITC were used in combination with anti-CD3 mAb conjugated with peridinin chlorophyll-alpha protein (PerCP) and phycoerythrin-labeled mAbs to CD4, CD8, CD19, or CD56. Among resting lymphocytes, CR3 was expressed on nearly all NK cells (CD56+CD3-), 1% of CD4+CD3+ helper T cells, 7% of CD8+CD3+ cytotoxic T cells, and 20% of B cells (CD19+). Among the 5% of T cells (CD3+) expressing CR3, the majority was CD56+. Incubation of PBMC for 30 min with PMA induced a three- to fivefold increase in CR3 expression on NK cells and a twofold increase on T cells but did not change the expression of CR3 on B cells. This effect of PMA was not blocked by the presence of cycloheximide, suggesting the presence of cytoplasmic (granule) stores of CR3 in these lymphoid cells resembling those previously reported in neutrophils and monocytes. When PBMC were incubated with rIFN-alpha, rIL-2, beta-glucan, or high concentrations of LPS, expression of CR3 on NK cells increased significantly, but > or = 4 hr of stimulation was required. Other cytokines (rIFN-gamma, rIL-1, rIL-4, rIL-6, TNF-alpha) and rC5a had no significant effect on CR3 expression. Among NK cells, both the CD56bright and the CD56dim cells expressed CR3, and the expression of CR3 on both of these NK cell subsets was increased in a similar manner by PMA. However, rIL-2 stimulated a greater increase in CR3 expression on CD56bright cells than on CD56dim cells. These studies suggest that CR3 expressed by NK cells or cytotoxic T cells resembles phagocyte CR3 in that cellular activation stimulates increased surface expression of CR3 derived from cytoplasmic reserves of the receptor.

Antibodies, Monoclonal↗
PubMed1993

Effect of nafamostat mesilate on Na+ and K+ transport properties in the rabbit cortical collecting duct.

1. To determine the mechanism(s) of hyperkalemia caused by nafamostat mesilate (NM), a serine-protease inhibitor, we investigated the effects of the drug on Na+ and K+ transport properties of the collecting duct (CD) cell in the isolated and perfused cortical collecting duct from rabbit kidneys. 2. NM at 10(-4) M in the lumen, hyperpolarized the apical membrane in parallel with increases in transepithelial resistance (RT) and fractional apical membrane resistance (fRA). 3. These effects were completely inhibited by pretreatment with 50 microM luminal amiloride, whereas they were not affected by luminal addition of 2 mM Ba2+. 4. NM at 10(-4) M in the bath slightly but significantly depolarized the basolateral membrane without any changes in RT or fRA, although NM at 10(-5) M in the bath had no effect on the electrical parameters. 5. It is concluded that NM mainly acts on the apical membrane of the CD cell and inhibits the amiloride-sensitive Na+ conductance in the apical membrane.

Amiloride↗
PubMed1993

Thyroid hormone stimulates Na(+)-K(+)-ATPase gene expression in cultured rat mesangial cells.

Thyroid hormone 3,3',5-triiodothyronine (T3) is an important regulator of Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) activity in a variety of mammalian target tissues. In the present study, we examined the expression of Na(+)-K(+)-ATPase alpha- and beta-subunit mRNAs by T3 in cultured rat mesangial cells. Northern blot analysis of total RNA isolated from cultured rat mesangial cells revealed the expression of mRNAs encoding Na(+)-K(+)-ATPase alpha 1- and beta 1-subunits; mRNAs encoding alpha 2- and alpha 3-subunits were undetectable. Exposure of mesangial cells to T3 (10(-8) M) caused a threefold increase in the alpha 1-mRNA expression, which was first detected at 6 h and sustained for at least 48 h. The beta 1-mRNA expression was gradually increased by T3, with a maximum fourfold elevation at 48 h. The 50% effective concentration (EC50) for the alpha 1- and beta 1-mRNA induction by T3 was approximately 10(-10) M. The half-life of alpha 1-mRNA analyzed by actinomycin D chase was approximately 3 h and was not affected by T3. The augmented alpha 1-mRNA expression by T3 was associated with a 2.4-fold increase in the alpha 1-subunit protein accumulation and a 1.6-fold increase in Na(+)-K(+)-ATPase activity. These data suggest that thyroid hormone stimulates Na(+)-K(+)-ATPase gene expression, protein accumulation, and enzyme activity in rat mesangial cells.

Animals↗
PubMed1993

Electrical properties of the rabbit cortical collecting duct from obstructed and contralateral kidneys after unilateral ureteral obstruction.

Electrophysiological techniques were used to determine the electrical properties of the collecting duct (CD) cell in the isolated cortical collecting duct from obstructed (UUOOK) and contralateral (UUOCK) kidneys in rabbits 24 h after unilateral ureteral obstruction (UUO); results were compared with those from sham-operated kidneys. The lumen-negative transepithelial voltage and the basolateral membrane voltage (VB) were decreased in the UUOOK, and increased in the UUOCK. The transepithelial conductance (GT) was decreased in parallel with an increase in the fractional apical membrane resistance (fRA) and a decrease in apical membrane conductance in the UUOOK. By contrast, the GT was increased in parallel with increases in apical and basolateral membrane conductances in the UUOCK. The amiloride-sensitive changes in apical membrane voltage (VA), GT and fRA were lower in the UUOOK, but greater in the UUOCK. The changes in VA and GT upon raising the perfusate K+ concentration and upon addition of luminal Ba2+ were decreased in the UUOOK, and increased in the UUOCK. Addition of ouabain to the bath resulted in a smaller depolarization of VB in the UUOOK, but in a greater depolarization in the UUOCK. Upon lowering bath Cl-, the change in basolateral membrane electromotive force (delta EMF) was increased in the UUOOK, and decreased in the UUOCK. Reversely, upon raising bath K+, the delta EMF was decreased in the UUOOK, and increased in the UUOCK. We conclude: (a) the conductances of Na+ and K+ in the apical membrane, and active Na(+)-K+ pump activity and relative K+ conductance in the basolateral membrane are decreased in the UUOOK, and increased in the UUOCK; (b) the relative basolateral membrane Cl- conductance was increased in the UUOOK, and decreased in the UUOCK.

Amiloride↗
PubMed1992

Purification of Chlamydomonas 28-kDa ubiquitinated protein and its identification as ubiquitinated histone H2B.

One of the most predominantly ubiquitinated protein species in Chlamydomonas, of which the apparent molecular mass in SDS-PAGE was 28 kDa, was found to exist abundantly in nuclei. The 28-kDa ubiquitinated protein was purified to homogeneity from the isolated nuclei of Chlamydomonas, and its partial amino acid sequence was determined. The N-terminal peptide sequence was identical with that of ubiquitin. Sequences homologous to those Chlamydomonas ubiquitin [corrected] and wheat histone H2B, and paired sequences of both of them were found in arginylendopeptidase-digested or protease V8-digested polypeptide fragments of the 28-kDa ubiquitinated protein. Based on these results, it was concluded that Chlamydomonas 28-kDa ubiquitinated protein is monoubiquitinated histone H2B.

Amino Acid Sequence↗
PubMed1992

Ca(2+)-dependent protein kinase from the halotolerant green alga Dunaliella tertiolecta: partial purification and Ca(2+)-dependent association of the enzyme to the microsomes.

Ca(2+)-dependent protein kinase (CDPK) was purified 900-fold from the soluble fraction of Dunaliella tertiolecta cells by ammonium sulfate precipitation, DEAE-Toyopearl, phenyl-Sepharose, and hydroxylapatite column chromatography. The CDPK was activated by micromolar concentration of Ca2+ and required neither calmodulin nor phospholipids for its activation. The enzyme phosphorylated casein, myosin light chain, and histone type III-S (histone H-1), but did not phosphorylate protamine and phosvitin. The Km values for ATP and casein were 11 microM and 300 micrograms/ml, respectively. Phosphorylation of casein was inhibited by calmodulin antagonists, calmidazolium, trifluoperazine, and compound 48/80, but not affected by calmodulin. CDPK bound to phenyl-Sepharose in the presence of Ca2+ and was eluted by ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA). This suggests that hydrophobicity of the enzyme was increased by Ca2+. CDPK was also bound to the microsomes isolated from Dunaliella cells in the presence of micromolar concentration of Ca2+ and released in the presence of EGTA, suggesting the possibility of in vivo Ca(2+)-dependent association of the enzyme. The enzyme phosphorylated many proteins in the microsomes but few in the cytosol, if at all.

Calmodulin↗
PubMed1992

Effect of insulin on potassium secretion in rabbit cortical collecting ducts.

Insulin is known to play an important role in the regulation of extrarenal K homeostasis. Previous clearance studies have shown that insulin decreases urinary K excretion, but the responsible nephron segments have not been identified. In this microperfusion study, in vitro, the effect of insulin on K transport in the cortical collecting duct (CCD), which is thought to be an important segment for regulation of the final urinary K excretion, was investigated. Basolateral insulin (10(-6) M) significantly inhibited net K secretion by 20% (mean JK = -26.2 +/- 4.2 peq.mm-1.min-1 for controls compared with -21.1 +/- 3.4 with insulin, P less than 0.001) and depolarized the transepithelial voltage (VT, from -14.6 +/- 3.5 to -10.8 +/- 3.5 mV, P less than 0.005), recovery did not occur over 60 min. Insulin (10(-11)-10(-5) M) depressed K secretion and depolarized the VT in a concentration-dependent manner. The half-maximal concentration was 5 x 10(-10) M, which is within the physiological range of plasma insulin concentration. In tubules of deoxycorticosterone acetate-treated rabbits, insulin also produced a significant fall in K secretion (from -43.4 +/- 7.5 to -36.1 +/- 5.7 peq.mm-1.min-1, P less than 0.05). Although luminal Ba (2 mM) decreased K secretion (from -14.4 +/- 2.9 to -7.0 +/- 1.7 peq.mm-1.min-1), basolateral insulin (10(-6) M) inhibited K secretion further (to -4.7 +/- 1.3 peq.mm-1.min-1, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1992

Interaction of Cl- and other halogens with Cl- transport systems in rabbit cortical collecting duct.

We have reported that in the rabbit cortical collecting duct (CCD) we can identify electrophysiologically three distinct cell types; the collecting duct (CD) cell and the alpha- and beta-intercalated (IC) cell. To further characterize the Cl- transport properties of each cell type, we examined the interaction between Cl- and other halogens or SCN- in the isolated and perfused CCD by intracellular microelectrode impalement. The rapid depolarization of the basolateral membrane potential (VB) caused by replacement of bath Cl- with each anion revealed that the sequences of apparent halogen selectivity for the basolateral Cl- conductance were similar in all three cell types. The ranking of Cl- > Br- > F- > I- corresponds to the sequence 5 of Eisenman's series, indicating "strong" interaction of the anions with the selectivity site. The basolateral Cl- conductance of these three cell types may share common characteristics, although I- permeability is less in IC cells than in CD cells. Hyperpolarization of the basolateral membrane of the beta-IC cell upon reduction of luminal Cl- reflects alterations in either Cl- entry across the apical membrane, or Cl- exit across the basolateral membrane, or both. Luminal Cl- replacement with each anion showed that the sequence of the hyperpolarization of the basolateral membrane was I- >> cyclamate = SCN- > F- > Br-, suggesting that I-inhibits either apical Cl- entry or basolateral Cl- exit. On the other hand, in the CD cell reduction of the perfusate Cl- by replacement with each anion caused the basolateral membrane to hyperpolarize with a different ranking: cyclamate = F- > I- = SCN- > Br-.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Regulation of Na,K-ATPase gene expression by thyroid hormone in rat cardiocytes.

Synthesis and activity of the enzymatic equivalent of the sodium pump, Na,K-ATPase, are regulated by thyroid hormone in responsive tissues. The purpose of this study was to determine whether triiodothyronine (T3) regulates the level of the messenger RNA (mRNA) coding for Na,K-ATPase alpha- and beta-subunits in the heart. The expression of Na,K-ATPase mRNAs in in vitro myocardial cells was directly assayed by Northern and slot blot hybridization using Na,K-ATPase alpha- and beta-isoform-specific cDNA probes. Exposure of cultured neonatal rat cardiocytes to 10(-8) M T3 resulted in 1) threefold to fourfold increase in alpha 1- and beta 1-mRNA accumulation, with a maximum elevation at 48 hours, 2) sevenfold increase in alpha 2-mRNA accumulation with a peak elevation at 72 hours, and 3) transient threefold increase in alpha 3-mRNA within the first 24 hours followed by a deinduction thereafter. The increase in alpha 1-mRNA accumulation by T3 occurred over the physiological T3 concentration range with an EC50 of 5 x 10(-10) M. This was associated with a twofold increase in alpha 1-subunit protein accumulation and an increase in Na,K-ATPase transport activity. The half-life of alpha 1-mRNA analyzed by actinomycin D chase was less than 3 hours and was not affected by T3. Transfection experiments with the luciferase reporter gene revealed that thyroid hormone response sequences are located within the 5'-flanking regions of each alpha-isoform gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of uninephrectomy on electrical properties of the cortical collecting duct from rabbit remnant kidneys.

Microelectrode techniques were used to determine the Na+ and K+ transport properties of the collecting duct cell in the isolated cortical collecting duct (CCD) from rabbits 14 d after uninephrectomy (UNX); results were compared with those from sham-operated rabbits (control). UNX had no effects on plasma aldosterone levels. The CCDs from UNX rabbits exhibited structural hypertrophy. The lumen negative transepithelial voltage and the basolateral membrane voltage (VB) were elevated in the UNX group. Although the transepithelial conductance (GT) and the fractional apical membrane resistance (fRA) were not different between the two groups, the conductances of the apical and the basolateral membranes were increased, and the tight junction conductance was decreased in the UNX group. The amiloride-sensitive changes in apical membrane voltage (VA), fRA, and GT were greater in the UNX group. The changes in VA upon raising the perfusate K+ concentration and the changes in VA and GT upon addition of Ba2+ to the perfusate were elevated in the UNX group. Upon raising K+ in the bath, a large depolarization of VB was observed in the UNX group. Lowering the bath Cl- resulted in a small depolarization of VB in the UNX group. Addition of Ba2+ to the bath in the UNX group caused the VB to hyperpolarize in parallel with decreases in GT and fRA whereas in the control group it had no effect on VB. Addition of ouabain to the bath resulted in a large depolarization of VB in the UNX group. We conclude that (a) UNX stimulates conductances of Na+ and K+ in the apical membrane, active Na(+)-K+ pump activity, and K+ conductance in the basolateral membrane, independently of plasma aldosterone; (b) The basolateral membrane in the tubules of UNX rabbits is more selective to K+; and (c) the hyperpolarization of VB upon UNX may increase passive K+ entry into the cell across the basolateral membrane.

Aldosterone↗