RESUMO
Spinocerebellar ataxia 2 (SCA2) is an autosomal dominant neurodegenerative disorder that results from the expansion of a cryptic CAG repeat within the exon 1 of the SCA2 gene. The CAG repeat in normal individuals varies in length from 14 to 31 repeats and is frequently interrupted by one or more CAA triplets, whereas the expanded alleles contain a pure uninterrupted stretch of 34 to 59 CAG repeats. We have previously reported the presence of a limited pool of 'ancestral' or 'at risk' haplotypes for the expanded SCA2 alleles in the Indian population. We now report the identification of two novel single nucleotide polymorphisms (SNPs) in exon 1 of the SCA2 gene and their characterization in 215 normal and 64 expanded chromosomes. The two biallelic SNPs distinguished two haplotypes, GT and CC, each of which formed a predominant haplotype associated with normal and expanded SCA2 alleles. All the expanded alleles segregated with CC haplotype, which otherwise was associated with only 29.3% of the normal chromosomes. CAA interspersion analysis revealed that majority of the normal alleles with CC haplotype were either pure or lacked the most proximal 5' CAA interruption. The repeat length variation at SCA2 locus also appeared to be polar with changes occurring mostly at the 5' end of the repeat. Our results demonstrate that CAA interruptions play an important role in conferring stability to SCA2 repeat and their absence predisposes alleles towards instability and pathological expansion. Our study also provides new haplotypes associated with SCA2 that should prove useful in further understanding the mutational history and mechanism of repeat instability at the SCA2 locus.
Assuntos
Proteínas/genética , Degenerações Espinocerebelares/genética , Repetições de Trinucleotídeos/genética , Alelos , Animais , Ataxinas , Cercopithecidae/genética , DNA/química , DNA/genética , Análise Mutacional de DNA , Evolução Molecular , Feminino , Variação Genética , Gorilla gorilla/genética , Haplótipos , Humanos , Macaca mulatta/genética , Macaca radiata/genética , Masculino , Repetições de Microssatélites , Dados de Sequência Molecular , Proteínas do Tecido Nervoso , Pan troglodytes/genética , Papio/genética , Mutação Puntual/genética , Polimorfismo de Nucleotídeo Único/genética , Expansão das Repetições de Trinucleotídeos/genéticaRESUMO
The suppression of contractility of rat portal vein caused by progesterone appears to be due to the potassium (K+) channel opening effect of this hormone. The identity of the specific K+ channels involved has been investigated using a variety of K+ channel blockers. Incubation with 100 nM iberiotoxin antagonised the progesterone-induced inhibition of spontaneous and 20 mM K+-induced phasic activity of the portal vein such that the contractions resembled those of the non-progesterone, non-iberiotoxin control tissues treated with the corresponding solvent vehicles. Incubation with barium chloride (20 and 100 microM), 4-aminopyridine (1 mM), tetraethylammonium chloride (1 mM), glibenclamide (1 microM) or apamin (1 microM) did not, however, have the same antagonistic effect. These results suggest that progesterone's selective suppression of rat portal vein contractility is mediated by the opening of BKCa channels.
Assuntos
Contração Muscular/efeitos dos fármacos , Músculo Liso Vascular/efeitos dos fármacos , Bloqueadores dos Canais de Potássio , Progesterona/antagonistas & inibidores , 4-Aminopiridina/farmacologia , Animais , Compostos de Bário/farmacologia , Cloretos/farmacologia , Glibureto/farmacologia , Hipoglicemiantes/farmacologia , Masculino , Peptídeos/farmacologia , Veia Porta , Ratos , Ratos WistarRESUMO
The mechanisms underlying the suppression of vasocontractility caused by progesterone were investigated by studying changes in the contractile force of rat isolated aorta and portal vein, induced by altering extracellular concentrations of noradrenaline (NA) potassium ions (K+) and calcium ions (Ca2+). In the aorta, progesterone (10 microM) had a general suppressive effect on NA-, Ca2+- and K+-induced contractions. In contrast, in the portal vein a more selective suppression of contractions was observed. Both tonic and phasic components of contractions induced by cumulative addition of Ca2+ to tissues equilibrated in Ca2+-free saline were suppressed. The phasic but not tonic components of contractions induced by NA addition were suppressed. There was no significant effect on tonic contractions induced by elevated (40-120 mM) K+, but a concentration-dependent suppression of the phasic component of contractions was observed during depolarisation with smaller elevations of K+ concentrations (5-20 mM). These results suggest that on the portal vein the suppressive effect of progesterone is due to a potassium channel opening action, whilst on the aorta a different or additional mechanism of suppression exists.