We report the molecular and functional characterization of murine Slc26a6, the putative apical chloride-formate exchanger of the proximal tubule. The Slc26a6 transcript is expressed in several tissues, including kidney. Alternative splicing of the second exon generates two distinct isoforms, denoted Slc26a6a and Slc26a6b, which differ in the inclusion of a 23-residue NH2-terminal extension. Functional comparison with murine Slc26a1, the basolateral oxalate exchanger of the proximal tubule, reveals a number of intriguing differences. Whereas Slc26a6 is capable of Cl−, SO[Formula: see text], formate, and oxalate uptake when expressed in Xenopus laevis oocytes, Slc26a1 transports only SO[Formula: see text] and oxalate. Measurement of intracellular pH during the removal of extracellular Cl− in the presence and absence of HCO[Formula: see text] indicates that Slc26a6 functions as both a Cl−/HCO[Formula: see text] and a Cl−/OH− exchanger; simultaneous membrane hyperpolarization during these experimental maneuvers reveals that HCO[Formula: see text] and OH− transport mediated by Slc26a6 is electrogenic. Cis-inhibition and efflux experiments indicate that Slc26a6 can mediate the exchange of both Cl− and SO[Formula: see text]with a number of substrates, including formate and oxalate. In contrast, SO[Formula: see text] and oxalate transport by Slc26a1 are mutually cis-inhibited but activated significantly by extracellular halides, lactate, and formate. The data indicate that Slc26a6 encodes an apical Cl−/formate/oxalate and Cl−/base exchanger and reveal significant mechanistic differences between apical and basolateral oxalate exchangers of the proximal tubule.

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The CCAAT/enhancer binding protein alpha (C/EBPalpha) and CCAAT/enhancer binding protein beta (C/EBPbeta) mRNAs are templates for the differential translation of several isoforms. Immunoblotting detects C/EBPalphas with molecular masses of 42, 38, 30, and 20 kDa and C/EBPbetas of 35, 20, and approximately 8.5 kDa. The DNA-binding activities and pool levels of p42(C/EBPalpha) and p30(C/EBPalpha) in control nuclear extracts decrease significantly whereas the binding activity and protein levels of the 20-kDa isoforms increase dramatically with LPS treatment. Our studies suggest that the LPS response involves alternative translational initiation at specific in-frame AUGs, producing specific C/EBPalpha and C/EBPbeta isoform patterns. We propose that alternative translational initiation occurs by a leaky ribosomal scanning mechanism. We find that nuclear extracts from normal aged mouse livers have decreased p42(C/EBPalpha) levels and binding activity, whereas those of p20(C/EBPalpha) and p20(C/EBPbeta) are increased. However, translation of 42-kDa C/EBPalpha is not down-regulated on polysomes, suggesting that aging may affect its nuclear translocation. Furthermore, recovery of the C/EBPalpha- and C/EBPbeta-binding activities and pool levels from an LPS challenge is delayed significantly in aged mouse livers. Thus, aged livers have altered steady-state levels of C/EBPalpha and C/EBPbeta isoforms. This result suggests that normal aging liver exhibits characteristics of chronic stress and a severe inability to recover from an inflammatory challenge.

The use of variable pitch or helix cutters is a known means to prevent chatter vibration during milling. In this article, an alternative method based on an improved semi-discretization method is proposed to predict the stability of variable pitch or variable helix milling. In order to consider the effect of distributed system delays attributed to helix variation, the average delays were calculated for each flute after the engaged cutting flutes were divided into a finite number of axial elements. Meanwhile, a straightforward integral force model, which can consider the piecewise continuous regions of the cutting that describe the helix angle is used to determine the cutting force. Through comparisons with prior works, timedomain simulations, and cutting tests, the proposed approach was verified. In addition, the method was applied to examine the effect of tool geometries on stability trends. Several phenomena for certain combinations of pitch and helix angles are shown and explained.