A sodium-independent neutral and basic amino acid transporter (NBAT) from rat kidney was recently cloned and its amino acid sequence deduced. We used light and electron microscopic immunoperoxidase labeling to determine the cellular localization of NBAT in rat kidney and small intestine. The localition was carried out using site-directed antisera raised against synthetic peptides within NBAT. The most prominent localization of NBAT was in microvilli of epithelial cells lining renal proximal tubules. Microvilli of small intesdnal epithelia were less frequently immunoreactive. Unexpectedly, the most intense labeling in the small intestine was seen within enteroendocrine cells and submucosal neurons. The neuronal labeling was highly localized within dense core vesicles in axon terminals apposed to the basal lamina near fenestrated blood vessels. These results support the proposal that NBAT plays a role in reabsorption of amino acids in renal tubules. In addition, they suggest that NBAT (or NBAT-like proteins) may have multiple functions in the small intestine, including luminal uptake of amino acids and vesicular uptake of related substrates into enteroendocrine cells and enteric neurons.

A recently cloned rat kidney protein (NBAT) mediates the sodium-independent transport of neutral as well as basic amino acids and cystine when expressed in Xenopus laevis oocytes. The human equivalent of this transporter may be the one that is defective in cystinuria. Immunocytochemical studies have indicated that NBAT is primarily localized in the brush border membranes of rat kidney and intestinal epithelial cells, a localization consistent with its proposed role in amino acid transport. Two contrasting topological models have been proposed for NBAT: a four membrane-spanning domain (MSD) Nin-Cin model and a single MSD Nin-Cout model. We have investigated the topology of this membrane protein using two different approaches. One method was an immunofluorescent labeling technique in which intact or membrane-permeabilized cells expressing NBAT were probed with antibodies directed against putative extracellular and intracellular domains of the protein. In the second method, fragments generated by limited surface proteolysis of intact brush border membrane vesicles were subjected to immunoblot analysis using several site-specific antibodies. Both approaches yielded results consistent with a four MSD Nin-Cin topological model for NBAT.

A prospective study was conducted over a 3-month winter period in three general practice clinics in an urban population in southern Israel to identify the etiological agents of respiratory tract infections (RTI) in adults. RTI was defined as an acute febrile illness with cough, coryza, sore throat or hoarseness. Serum samples were taken from all patients in both the acute and convalescent phases of their illness. Tests were conducted for detection of 17 microorganisms known to cause RTI, including serological tests for 16 known pathogens. An etiological diagnosis was established in 80 (66%) of the 122 patients who participated in the study. The distribution of the etiological agents was as follows: influenza B virus in 27 (22%) patients. Chlamydia pneumoniae in 22 (18%), Legionella spp. in 15 (12%), Mycoplasma pneumoniae in 13 (11%), influenza A virus in 11 (9%), Bordetella pertussis in 9 (7%), adenovirus in 4, Epstein Barr virus in 4, Haemophilus influenzae in 3, beta-hemolytic streptococci in 3, Streptococcus pneumoniae in 2, respiratory syncytial virus in 2, parainfluenza 1 virus in 2 and parainfluenza 2 virus in 1. No patients were found to be infected with Coxiella burnetii, Moraxella catarrhalis or parainfluenza 3 virus. More than one pathogen was identified in 27 (34%) patients in whom an etiological diagnosis was established. It is concluded that RTI is caused by a broad spectrum of etiological agents, a considerable number of patients having evidence of infection with more than one pathogen. The therapeutic significance of these findings should be elucidated in further studies.

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The Na+-independent neutral amino acid transporter (NAA-Tr) that we had previously cloned from rat kidney has been investigated with respect to its disributlop in mammalian tissues and cells.'By Northern blot analysis and RNase protection assay, a 2.4-kilobase (kb) mRNA in rat intestie was found to be identical to that in rat kidney. Of the other rat tissues examined, only brain and heart were found to contain mRNAs related to kidney NAA-Tr by Northern amay. However, these were larger (-5 and~7 kb). Mouse and rabbit kidney also contain mRNAs of 2.4 kb that exhibited a high degree of homology with rat kidney NAA-Tr. Of the several cultured cells investigated that demonstrated considerable Na+-independent neutral amino acd tran rt activity, only human colon carcinoma (Caco) cells were positive by Northern assay. The failure to detect NAA-Tr mRNA in many cells and tissues that carry out Na+-independent transport indites that unrelated transporters must also exist. Cells and tissues that were negative with respect to rat kidney NAA-Tr as well as those that were positive transported leudne and trptophan equally well. However, when mRNA from the same cells and tissues was expressed in oocytes, in all cams tryptophan was t d far less efficiently than leucine. This defect in tryptophan transport is apparently due to aberrant expression of neutral amino acid transporters in general in Xenopus oocytes.We recently reported the cloning and sequencing of a cDNA encoding a sodium-independent L-type neutral amino acid transporter (NAA-Tr) from rat kidney (1). When the complementary RNA (cRNA) transcribed from this clone was injected into Xenopus laevis oocytes, transport activity was expressed that was similar to that of the well-characterized L-type system (see ref. tTo whom reprint requests should be addressed. 9982The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.