RESUMO
Phospholemman (PLM), the major sarcolemmal substrate for phosphorylation by cAMP-dependent kinase (PKA) protein kinase C (PKC) and NIMA kinase in muscle, induces hyperpolarization-activated anion currents in Xenopus oocytes, most probably by enhancing endogenous oocyte currents. PLM peptides from the cytoplasmic tail are phosphorylated by PKA at S68, by NIMA kinase at S63, and by PKC at both S63 and S68. We have confirmed the phosphorylation sites in the intact protein, and we have investigated the role of phosphorylation in the regulatory activity of PLM using oocyte expression experiments. We found: (1) the cytoplasmic domain is not essential for inducing currents in oocytes; (2) co-expression of PKA increased the amplitude of oocyte currents and the amount of PLM in the oocyte membrane largely, but not exclusively, through phosphorylation of S68; (3) co-expression of PKA had no effect on a PLM mutant in which all putative phosphorylation sites had been inactivated by serine to alanine mutation (SSST 62, 63, 68, 69 AAAA); (4) co-expression of PKC had no effect in this system; (5) co-expression of NIMA kinase increased current amplitude and membrane protein level, but did not require PLM phosphorylation. These findings point to a role for phosphorylation in the function of PLM.
Assuntos
Proteínas de Ciclo Celular , Canais Iônicos/biossíntese , Proteínas de Membrana/metabolismo , Oócitos/metabolismo , Fosfoproteínas/metabolismo , Proteínas Quinases/biossíntese , Sequência de Aminoácidos , Animais , Sítios de Ligação , Membrana Celular/metabolismo , Canais de Cloreto/biossíntese , Proteínas Quinases Dependentes de AMP Cíclico/biossíntese , Expressão Gênica , Proteínas de Membrana/química , Dados de Sequência Molecular , Quinase 1 Relacionada a NIMA , Quinases Relacionadas a NIMA , Fosfoproteínas/química , Fosforilação , Proteína Quinase C/biossíntese , Proteínas Serina-Treonina Quinases/biossíntese , Regulação para Cima , XenopusRESUMO
The cases of a forty-five-year-old woman and a twenty-year-old man who developed severe intraarticular and periarticular heterotopic ossification around the knee following intramedullary nailing of a femur fracture using a retrograde technique. The association of musculoskeletal heterotopic ossification with closed head injuries seems well established and can occur in and around the knee following retrograde intramedullary nailing. This complication may occur more often than has been reported.
Assuntos
Fraturas do Fêmur/cirurgia , Fixação Intramedular de Fraturas/efeitos adversos , Articulação do Joelho/diagnóstico por imagem , Ossificação Heterotópica/diagnóstico por imagem , Ossificação Heterotópica/etiologia , Acidentes de Trânsito , Adulto , Artroscopia/métodos , Parafusos Ósseos/efeitos adversos , Desbridamento/métodos , Feminino , Fraturas do Fêmur/diagnóstico por imagem , Seguimentos , Fixação Intramedular de Fraturas/métodos , Humanos , Escala de Gravidade do Ferimento , Articulação do Joelho/cirurgia , Masculino , Pessoa de Meia-Idade , Traumatismo Múltiplo/diagnóstico , Traumatismo Múltiplo/terapia , Ossificação Heterotópica/cirurgia , Radiografia , Amplitude de Movimento Articular , Resultado do TratamentoRESUMO
In myotonic muscular dystrophy, abnormal muscle Na currents underlie myotonic discharges. Since the myotonic muscular dystrophy gene encodes a product, human myotonin protein kinase, with structural similarity to protein kinases, we tested the idea that human myotonin protein kinase modulates skeletal muscle Na channels. Coexpression of human myotonin protein kinase with rat skeletal muscle Na channels in Xenopus oocytes reduced the amplitude of Na currents and accelerated current decay. The effect required the presence of a potential phosphorylation site in the inactivation mechanism of the channel. The mutation responsible for human disease, trinucleotide repeats in the 3' untranslated region, did not prevent the effect. The consequence of an abnormal amount of the kinase would be altered muscle cell excitability, consistent with the clinical finding of myotonia in myotonic dystrophy.