Neuronal nicotinic acetylcholine receptors on bovine chromaffin cells: Cloning, expression, and genomic organization of receptor subunits

Neuronal nicotinic acetylcholine receptors from bovine adrenomedullary chromaffin cells play a primary role in triggering catecholamine secretion. In the present study, their constituent subunits were characterized. In addition to the α3 subunit, which we have previously cloned, the presence of α5 and β4 but not of β2 subunits was detected by reverse transcription-PCR analysis of mRNA from adrenal medulla. In situ hybridization indicated that α3, α5, and β4 subunits are coexpressed in all chromaffin cells. The primary structure of α5 and β4 subunits was determined and functional receptors were obtained upon coinjection of subunit cRNAs into Xenopus oocytes. In contrast to other β4-containing nicotinic receptors, the ones formed by the bovine β4 subunit are insensitive to the agonist cytisine. Finally, we characterized the intergenic region of α3 and α5 subunits, which together with the β4 subunit, form a gene cluster in rats and chickens. RNase assays and the existence of overlapping cDNAs indicate that, in the bovine genome, the α3 and α5 genes overlap at their 3′ ends. This fact is probably due to inefficient transcription termination, as a result of weak polyadenylation signals.Thisstudywassupportedbygrants fromtheMinistriesofEducation(DGICYT,PB92-0346, andPB93-093l)andHealth(Fis95/1672)ofSpain,the CommissionoftheEuropeanEconomicCommunity (SC1*CT91-0666),GeneralitatValenciana(GV-2535/94), andtheWellcomeTrust(039284).A.C.-C.wasapredoctoralfellowoftheEuropeanEconomicCommunity.F.I.S. wasapostdoctoralfellowoftheWellcomeTrust.E.D.del T.andF.V.-A.weretherecipientsofpredoctoralfellowships fromtheMinistryofEducationofSpain.J.C.wasapredoctoralfellowofFundacionCAM.Peer reviewe

Resultados a largo plazo del tratamiento de las perforaciones timpánicas con hialuronidato sódico

Hacemos un estudio en pacientes con perforaciones timpánicas analizando los resultados obtenidos tras un tratamiento con hialuronidato sódico, el cual parece jugar un papel en el estimulo de la reepitelizació

Tuberculosis amigdalar. Apropósito de un caso

Se presenta un caso de tuberculosis amigdalar en una paciente de 80 años. Se consideran las manifestaciones clínicas y la dificultad del diagnóstico. Se realiza una revisión de la literatur

Linfoma nasal angiocéntrico natural killer. Una entidad clinicopatológica distinta

Los linfomas de células T/natural Killer (NK) representan una entidad clínico patológica distinta (1) caracterizada por la presencia de lesiones necróticas progresivas, la expresión de un marcador tumoral asociado a las células NK, el CD 56, y su íntima relación con el virus de Epstein-Barr (VEB) . Presentamos un caso de linfoma nasal angiocéntrico NK, diagnosticado tras un año de historia de obstrucción nasal

Immunohistochemical localization of the voltage-gated potassium channel subunit Kv1.4 in the central nervous system of the adult rat

A large set of voltage-gated potassium channels is involved in regulating essential aspects of neuronal function in the central nervous system, thus contributing to the ability of neurons to respond to a given input. In the present study, we used immunocytochemical methods to elucidate the regional, cellular and subcellular distribution of the voltage-gated potassium channel subunit Kv1.4, a member of the Shaker subfamily, in the brain. At the light microscopic level, the Kv1.4 subunit showed a unique distribution pattern, being localized in specific neuronal populations of the rat brain. The neuronal regions expressing the highest levels of Kv1.4 protein included the cerebral cortex, the hippocampus, the posterolateral and posteromedial ventral thalamic nuclei, the dorsolateral and medial geniculate nuclei, the substantia nigra and the dorsal cochlear nucleus. The Kv1.4 subunit was also present in other neuronal populations, with different levels of Kv1.4 immunoreactivity. In all immunolabeled regions, the Kv1.4 subunit was mostly diffusely distributed and, to a lesser extent, it stained cell bodies and proximal dendrites. Furthermore, Kv1.4 immunoreactivity was also detected in nerve terminals and axonal terminal fields. At the electron microscopic level, Kv1.4 was located postsynaptically in dendritic spines and shafts at extrasynaptic sites, as well as presynaptically in axon and active zone of axon terminals, in the neocortex and hippocampus. The findings indicate that Kv1.4 channels are widely distributed in the rat brain and suggest that activation of this channel would have different modulatory effects on neuronal excitability.This work was supported by a grant from the Spanish Ministry of Education (DGES PM 97-0082) to J.M.J. C.C.V. was supported by grants GC 02034 and FIS 01/3018.Peer reviewe

Osteomielitis del seno frontal. Caso clínico.

Se presenta un caso de osteomielitis del seno frontal con destrucción de tabla interna. Revisamos la etiología, vías de propagación, diagnóstico y tratamient

Differential expression of α-bungarotoxin-sensitive neuronal nicotinic receptors in adrenergic chromaffin cells: A role for transcription factor Egr-1

Adrenomedullary chromaffin cells express at least two subtypes of acetylcholine nicotinic receptors, which differ in their sensitivity to the snake toxin α-bungarotoxin. One subtype is involved in the activation step of the catecholamine secretion process and is not blocked by the toxin. The other is α-bungarotoxin-sensitive, and its functional role has not yet been defined. The α7 subunit is a component of this subtype. Autoradiography of bovine adrenal gland slices with α-bungarotoxin indicates that these receptors are restricted to medullary areas adjacent to the adrenal cortex and colocalize with the enzyme phenylethanolamine N-methyl transferase (PNMT), which confers the adrenergic phenotype to chromaffin cells. Transcripts corresponding to the α7 subunit also are localized exclusively to adrenergic cells. To identify possible transcriptional regulatory elements of the α7 subunit gene involved in the restricted expression of nicotinic receptors, we isolated and characterized its 5′ flanking region, revealing putative binding sites for the immediate early gene transcription factor Egr-1, which is known to activate PNMT expression. In reporter gene transfection experiments, Egr-1 increased α7 promoter activity by up to sevenfold. Activation was abolished when the most promoter-proximal of the Egr-1 sites was mutated, whereas modification of a close upstream site produced a partial decrease of the Egr-1 response. Because Egr-1 was found to be expressed exclusively in adrenergic cells, we suggest that this transcription factor may be part of a common mechanism involved in the induction of the adrenergic phenotype and the differential expression of α-bungarotoxin-sensitive nicotinic receptors in the adrenal gland.This work was supported by Grants from the Ministries of Education (Direccion General de Investigacion Cientifica yTecnica:PB92-0346,PB95-0690, and PB930931) and Health (Fis95/1672) of Spain,the Commission of the European Economic Community (SC1*CT91-0666),Generalitat Valenciana(GV-D-VS-20-15896), and the WellcomeTrust(039284).E.D. del T. was the recipient of a predoctoral fellowship from the Ministry of Education of Spain.F.I.S.was a postdoctoral fellow of theWellcomeTrust.C.C.-S. wasthe recipient of a fellowship from Generalitat Valenciana.Peer reviewe