Immunocytochemical localization of (Na+ + K+)-ATPase in the rat hippocampus

Insulin receptor-related receptor expression in non-A intercalated cells in the kidney

Insulin receptor- related receptor (IRR) is a novel receptor tyrosine kinase in the insulin receptor family. Previous studies have demonstrated that the mammalian organ with the highest level of IRR mRNA is the kidney. By in situ hybridization, kidney expression of IRR transcript is only in the distal nephron and the collecting ducts; however, the specific cellular distribution of IRR is unknown. The purpose of this study was to examine IRR protein expression in the adult mouse kidney using immunohistochemical techniques. IRR was specifically present in a subset of cells in the connecting tubule, the initial collecting tubule, and the cortical collecting duct. IRR protein is detected in cells that express vacuolar H+-ATPase and carbonic anhydrase 2, but not in cells that express band 3 (anion exchanger 1). In the cortical collecting duct, the IRR positive cells are likely B intercalated cells. In the connecting tubule and the initial collecting tubule, the cells are B cells and/or non-A non-B cells. Thus, IRR is a specific marker for non-A intercalated cells in the kidney.

The presence of both negative and positive elements in the 5'-flanking sequence of the rat Na,K-ATPase alpha 3 subunit gene are required for brain expression in transgenic mice

The Na,K-ATPase is an integral plasma membrane protein consisting of alpha and beta subunits, each of which has discrete isoforms expressed in a tissue-specific manner. Of the three functional alpha isoform genes, the one encoding the alpha 3 isoform is the most tissue-restricted in its expression, being found primarily in the brain. To identify regions of the alpha 3 isoform gene that are involved in directing expression in the brain, a 1.6 kb 5'-flanking sequence was attached to a reporter gene, chloramphenicol acetyltransferase (CAT). The alpha 3-CAT chimeric gene construct was microinjected into fertilized mouse eggs, and transgenic mice were produced. Analysis of adult transgenic mice from different lines revealed that the transgene is expressed primarily in the brain. To further delineate regions that are needed for conferring expression in this tissue, systematic deletions of the 5'-flanking sequence of the alpha 3-CAT fusion constructs were made and analyzed, again using transgenic mice. The results from these analyses indicate that DNA sequences required for mediating brain-specific expression of the alpha 3 isoform gene are present within 210 bp upstream of the transcription initiation site. alpha 3-CAT promoter constructs containing scanning mutations in this region were also assayed in transgenic mice. These studies have identified both a functional neural-restrictive silencer element as well as a positively acting cis element.

Postnatal development of electrogenic sodium pump activity in rat hippocampal pyramidal neurons

We assessed the development of electrogenic sodium pump (Na+ pump) activity in CA1 pyramidal neurons of rat hippocampal slices by studying the prolonged hyperpolarization which follows glutamate-induced depolarization (postglutamate hyperpolarization or PGH) at different postnatal ages. We also examined the development of membrane-bound enzyme in the hippocampal CA1 subfield with light microscopic immunocytochemistry and an antiserum against Na+,K(+)-ATPase. The PGH, which has previously been shown to be due to activation of an electrogenic Na+ pump in adult hippocampal CA1 neurons, was eliminated by strophanthidin, a Na+,K(+)-ATPase inhibitor, at all ages. It was unaffected by several potassium channel blockers, an intracellular calcium chelator, intracellular Cl- injection or tetrodotoxin (TTX) perfusion. The PGH thus appeared to be independent of K+ and Cl- conductances and produced by an electrogenic Na+ pump in adult and immature animals activated in large part by entry of Na+ through the glutamate receptor-channel complex. The size (integrated area) of the PGH was directly proportional to the area of preceding glutamate-induced depolarization (GD) and relatively voltage independent. Similar GDs could be elicited from postnatal day (P) 7 to P greater than or equal to 35, however, only very small PGHs were produced in neurons from P7-11 animals. A ratio of PGH area to GD area (PGH ratio) was calculated for each neuron and used to compare Na+ pump activity at different ages. There was a significant increase in the mean PGH ratio with age when P7-11, P21-25 and P35-39 groups were compared. Na+ pump activity estimated from the PGH ratio is very low in the first postnatal week but develops gradually over the first 5 weeks of life. Immunostaining for Na+,K(+)-ATPase in adult rat hippocampi revealed a punctate reaction product surrounding pyramidal cell bodies, whereas the staining was uniform along plasmalemma of dendrites in stratum radiatum and stratum oriens. By contrast, only minimum staining was present surrounding cell bodies and dendrites of P7 hippocampi and staining in stratum pyramidale was not punctate at this age. Na+,K(+)-ATPase activity estimated grossly from immunocytochemical staining is very low in the first postnatal week, increases during the first 5 weeks and develops a characteristic focal localization.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential distribution of (Na,K)-ATPase alpha isoform mRNAs in the peripheral nervous system

mRNA transcripts for 3 isoforms of the alpha subunit of (Na,K)-ATPase have been previously identified in the nervous system (designated alpha 1, alpha 2, and alpha 3). In order to study the localization and expression of the different alpha isoforms in the peripheral nervous system, we prepared probes from the unique 3' untranslated region of alpha 1 cDNA, and from the translated region of alpha 3 cDNA. These probes were used in dot blot and in situ hybridization assays of rat spinal cord, dorsal root ganglia (DRG), and sciatic nerve. Within the ventral horn of lumbar spinal cord, alpha 1 mRNA was found in a discrete set of laterally placed motor neurons, while alpha 3 was found in all the identified neurons of the spinal cord, including those motor neurons containing alpha 1. In the lumbar DRG, alpha 3 was uniformly distributed in DRG neurons, while alpha 1 was abundant in some neurons but little or none was found in other neurons. Satellite cells contained neither isoform. Schwann cells in sciatic nerve were labeled with the alpha 1 probe in a perinuclear distribution, but contained no detectable alpha 3. Dot blot analysis showed alpha 1 and alpha 3 in spinal cord and DRG, but only alpha 1 in peripheral nerve.(ABSTRACT TRUNCATED AT 250 WORDS)