Role of actin in the cAMP-dependent activation of sodium/glucose cotransporter in renal epithelial cells

We examined whether actin filaments are involved in the cAMP-dependent activation of a high affinity sodium/glucose cotransporter (SGLT1) using epithelial expression systems. The expression of enhanced green fluorescent protein-tagged SGLT1 (EGFP-SGLT1) in Madin-Darby canine kidney (MDCK) cells was revealed by Western blotting and confocal laser microscopy. 8-Br-cAMP, a membrane permeable cAMP analog, enhanced [¹⁴C]-α-methyl glucopyranoside ([¹⁴C]-AMG) uptake. Both basal and 8-Br-cAMP-elicited [¹⁴C]-AMG uptakes were inhibited by N-(2{[3-(4-bromophenyl)-2-propenyl]-amino}-ethyl)-5-isoquinolinesulfonamide (H-89), a protein kinase A inhibitor, and cytochalasin D, an actin filament formation inhibitor. Furthermore, cytochalasin D inhibited the distribution of EGFP-SGLT1 at the apical surface. These results suggest that the EGFP-SGLT1 protein is functionally expressed in the apical membrane of MDCK cells, and is up-regulated by a cAMP-dependent pathway requiring intact actin filaments.     

Role of virus inhibitory factor or interferon in the antitumoral effect of whole-body hyperthermia

The interferon inducing effect of hyperthermia was studied in normal and tumor-bearing mice. Circulating interferon was temporarily detected one day after subcutaneous transplantation of 1.6 X 10(6) Ehrlich's ascites tumor cells. Hyperthermia of 43.5 degrees C for 5 min did not induce the interferon formation in mice with or without subcutaneous tumor of the cells. These findings showed that the induction of interferon formation was not main cause of the hyperthermia-induced tumor inhibition.     

Gap Junctions Mediate Glucose Transport Between GLUT1-Positive and -Negative Cells in the Spiral Limbus of the Rat Cochlea

To elucidate the role of the spiral limbus in glucose transport in the cochlea, we analyzed the expression and localization of GLUT1, connexin26, connexin30, and occludin in the spiral limbus of the rat cochlea. GLUT1 and occludin were detected in blood vessels. GLUT1, connexin26, connexin30, and occludin were also expressed in fibrocytes just basal to the supralimbal lining cells. Connexin26 and connexin30 were present among not only these GLUT1-positive fibrocytes but also GLUT1-negative fibrocytes. In vivo glucose imaging using 6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-6-deoxyglucose (6-NBDG, MW 342) together with Evans Blue Albumin (EBA, MW 68,000) showed that 6-NBDG was rapidly distributed throughout the spiral limbus, whereas EBA was localized only in the vessels. Moreover, the gap junctional uncoupler heptanol inhibited the distribution of 6-NBDG. These findings suggest that gap junctions play an important role in glucose transport in the spiral limbus, i.e., that gap junctions mediate glucose transport from GLUT1-positive fibrocytes to GLUT1-negative fibrocytes in the spiral limbus.     

Disappearance of terminal deoxynucleotidyltransferase in human malignant T-lymphoblasts treated with a human alpha interferon preparation

Human T-lymphoblastoid cell lines RPMI 8402, MOLT-3, and CCRF-CEM were treated with interferon (IFN) to determine if the treatment would result in the disappearance of cellular terminaldeoxynucleotidyltransferase (TdT), a possible differentiation marker for T-lymphocytes. Incubation of RPMI 8402 cells in the presence of IFN preparation caused a decrease in the number of TdT-positive cells and in TdT activity of the cell extract. The inhibition of cell multiplication was dose dependent. The anticellular effect of IFN preparation was cytostatic, not cytocidal. The IFN preparation modified neither the TdT content nor proliferation of MOLT-3 and CCRF-CEM cell lines. The effects of IFN preparation thus varied with the cell line.     

Wavelength Effect on the Action of a N-Phenylimide S-23142 and a Diphenylether Acifluorfen-Ethyl in Cotyledons of Cucumber (Cucumis sativus L.) Seedlings

Specific wavelengths of light required for expression of phytotoxic activity of S-23142 (N-[4-chloro-2-fluoro-5-propargyloxy]phenyl-3,4,5,6-tetra- hydrophthalimide) and acifluorfen-ethyl (ethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitro benzoic acid) were determined in cotyledons of cucumber seedlings using the Okazaki Large Spectrograph. Leakage of amino acids from the cotyledons was measured as an indication of the phytotoxic activity. The wavelength effects showed common major peaks of activity at 550 and 650 nanometers and a minor peak at 450 nanometers for both herbicides, indicating a common primary photoreaction. Concomitant application of DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea) with S-23142 had little influence on the effective wavelengths for S-23142 activity. Light of 450 and 650 nanometers was relatively less effective in achlorophyllous tissue grown in far red light than in green tissue. These results strongly suggest that the phytotoxic action of S-23142 and diphenylethers involves multiple photoreactions and that one of the photoreceptor pigments may be chlorophyll or its related pigment, although photosynthesis is not involved.     

Primary structures of two types of alpha-subunit of rat brain Na+,K+,-ATPase deduced from cDNA sequences

A rat brain cDNA library was screened by using as a probe a fragment of cDNA encoding the alpha-subunit of human Na+,K+-ATPase. Two different cDNA clones were obtained and analyzed. One of them was concluded to be a cDNA encoding the alpha-subunit of the weakly ouabain-sensitive rat kidney-type Na+,K+-ATPase. The deduced amino acid sequence consists of 1,018 amino acids. The alpha-subunit of the rat kidney-type Na+,K+-ATPase shows 97% homology in amino acid sequence with the alpha-subunit of human, sheep, or pig enzyme and 87% with that of Torpedo. Based on a comparison of the amino acid sequence at the extracellular domain of the alpha-subunit between weakly ouabain-sensitive rat kidney-type enzyme and the ouabain-sensitive human, sheep, pig, or Torpedo enzyme, it was proposed that only two significant amino acid replacements are unique to the rat kidney-type alpha-subunit. Another cDNA clone obtained showed 72% homology in nucleotide sequence with the former cDNA coding the alpha-subunit of the rat kidney-type Na+,K+-ATPase and the deduced amino acid sequence exhibited 85% homology with that of the alpha-subunit of rat kidney-type Na+,K+-ATPase.