Evidence against bicarbonate reabsorption in the ascending limb, particularly as disclosed by free-water clearance studies.

Bicarbonate reabsorption in the thick ascending limb of Henle's loop was examined by studies of free-water clearance (CH2O) and free-water reabsorption (TcH2O). During maximal water diuresis in the dog, CH2O/GFR was taken as an indes of sodium reabsorption in, and urine flow (V/GFR) as an index of delivery of filtrate to, this scarbonate, infusion of a nonreabsorbable solute (hypotonic mannitol) and administration of an inhibitor of bicarbonate reabsorption (acetaent, but less than that achieved with hypotonic saline infusion. This suggests that sodium that sodium bicarbonate is not reabsorbed in the ascending limb. Rather, it is the sodium chloride, swept out of the proximal tubule by osmotic diuresis due to nonreabsorbed mannitol or sodium bicarbonate, that is reabsorbed in the ascending limb thereby increasing CH2O, whereas the nonreabsorption of mannitol and sodium bicarbonate results in a depressed CH20 per unit V when compared with hypotonic saline. V/GFR is not a satisfactory index of delivery to the ascending limb during osmotic diuresis, since it includes water obligated by nonreabsorbable solutes. When a better index of delivery, the sum of the clearances of chloride (CC1) and free-water (CH2O) is used, hypotonic bicarbonate infusion, hypotonic mannitol infusion and acetazolamide administration increase CH2O/GFR per unit delivery to the same extent as odes hypotonic saline infusion. Studies in dogs and rats on TcH2O also indicate that sodium bicarbonate is an impermeant solute in the ascending limb. Osmotic diuresis due to sodium bicarbonate diuresis, produced either by inhibition of sodium bicarbonate reabsorption (acetazolamide, L-lysine mono-hydrochloride) or infusion of sodium bicarbonate, or mannitol diuresis both produced marked chloruresis and increased TcH2O to the same extent as did hypertonic saline infusion. If chloride excretion was almost eliminated by hemodialysis against a chloride-free dialysate (dogs) or prolonged feeding of a salt-free diet (rats), TcH2O formation was unimpaired if hypertonic saline was infused but virtually obliterated during mannitol or sodium bicarbonate diuresis. Sodium reabsorption in the ascending limb, therefore, appears to be dependent upon chloride as the accompanying anion. At any given rate of bicarbonate excretion, more cloride is delivered out of the proximal tubule (as estimated from CC1 + CH2O) with hypotonic sodium bicarbonate infusion than with acetazolamide administration. This suggests that magnitude of the chlorutesis accompanying bicarbonate diuresis depends, not only on osmotic diuresis due to nonreabsorbed sodium bicarbonate, but also on the extent to which concomitant changes in effective extracellular volume influence overall sodium chloride reabsorption.     

Immunohistochemical localization of glandular kallikrein in the endocrine and exocrine human pancreas

Fab fragments from two new monospecific anti-human tissue kallikrein sera were examined for their capacity to inhibit the functional activities of purified human urinary kallikrein and purified human pancreatic kallikrein. Fragments from a new anti-urinary kallikrein serum and from an anti-pancreatic kallikrein serum yielded mixed inhibition of kinin-generating activity and minimal inhibition of esterolytic activity. In contrast to the previously described "active site directed" anti-urinary kallikrein, these new antisera demonstrated little specificity for epitopes near the enzymatic site of urinary or pancreatic kallikrein. When used to localize kallikrein antigen in human pancreas obtained at surgery, IgG fractions of the new anti-kallikrein sera yielded moderate acinar and ductal staining in the absence of pretreatment of the tissue with trypsin or pronase. Short incubation with 0.125 mg/ml of either enzyme permitted the discrete localization of islet beta cell kallikrein antigen, while increased pronase concentrations decreased kallikrein antigen in both islets and exocrine tissue and led to islet destruction. Both antibody specificity and tissue preparation influence kallikrein localization in human pancreas.     

Chromosomal Localization of the Human and Mouse Hyaluronan Synthase Genes

We have recently identified a new vertebrate gene family encoding putative hyaluronan (HA) synthases. Three highly conserved related genes have been identified, designatedHAS1, HAS2,andHAS3in humans andHas1, Has2,andHas3in the mouse. All three genes encode predicted plasma membrane proteins with multiple transmembrane domains and approximately 25% amino acid sequence identity to theStreptococcus pyogenesHA synthase, HasA. Furthermore, expression of any oneHASgene in transfected mammalian cells leads to high levels of HA biosynthesis. We now report the chromosomal localization of the threeHASgenes in human and in mouse. The genes localized to three different positions within both the human and the mouse genomes.HAS1was localized to the human chromosome 19q13.3–q13.4 boundary andHas1to mouse Chr 17.HAS2was localized to human chromosome 8q24.12 andHas2to mouse Chr 15.HAS3was localized to human chromosome 16q22.1 andHas3to mouse Chr 8. The map position forHAS1reinforces the recently reported relationship between a small region of human chromosome 19q and proximal mouse chromosome 17.HAS2mapped outside the predicted critical region delineated for the Langer–Giedion syndrome and can thus be excluded as a candidate gene for this genetic syndrome.     

Partial Structure, Chromosome Localization, and Expression of the MouseGirk4Gene

The G protein-gated potassium channel I_KAChconstitutes part of a signaling pathway that mediates the negative chronotropic and inotropic effects of acetylcholine on cardiac physiology. Similar or identical ion channels regulate the excitability of many neurons in response to neurotransmitters. I_KAChis composed of two homologous subunits, GIRK1 and GIRK4. Here we describe a partial genomic structure of the mouseGirk4gene. Two exons containing the complete protein-coding sequence were identified.Girk4was mapped to mouse chromosome 9 (13 cM), consistent with the mapping of humanGIRK4to chromosome 11q23–ter. GIRK4 mRNA was found mainly in mouse heart, with trace levels detected in brain, kidney, lung, and spleen. No detectable levels were observed in skeletal muscle, liver, and testis. The onset of GIRK4 mRNA expression in the developing mouse occurs between Embryonic Days 7 and 11, consistent with the appearance and function of the mouse heart.     

Physical and genetic linkage of the genes encoding Ly-9 and CD48 on mouse and human chromosomes 1

By virtue of sequence similarity, the genes encoding CD2, CD48, CD58, and Ly-9 have been assigned to a distinct subset within the immunoglobulin superfamily. Previous gene mapping studies in human and mouse have suggested that CD2, CD48, and CD58 arose by gene duplication. Here we show the gene encoding Ly-9 to be located adjacent to CD48 and the Na,K-ATPase 2 subunit gene on human and mouse chromosome 1. The proximity in human and mouse genomes of the genes encoding CD2, CD58, and the Na,K-ATPase 1 subunit, and of the Ly-9, CD48, and the Na,K-ATPase 2 subunit genes may be explained by the occurence of two, successive duplication events during vertebrate evolution, and suggest that Ly-9 may also participate in adhesion reactions between T lymphocytes and accessory cells by homophilic interaction.