These results indicate that Panx1 is the principal route of ATP release in control and mdx muscle fibers. == ATP-dependent Excitation-transcription Coupling is Altered in Adult Dystrophic Muscle Fibers == It has been shown that Panx1 is present in both sarcolemma and T-tubules of skeletal muscle fibers[11], where it can interact with the L-type Ca2+channel Cav1.1. pro-apoptotic, inducing the transcription of Bax, Bim and PUMA and increasing the levels of activated Bax and cytosolic cytochrome c. These evidence points to an involvement of the ATP pathway in the activation of mechanisms related with cell death in Isochlorogenic acid B muscular dystrophy, opening new perspectives towards possible targets for pharmacological therapies. == Introduction == ATP was considered for a long time as a molecule exclusively involved in cell energy and metabolism. Nevertheless, in the past years, ATP has been Isochlorogenic acid B shown to be an important extracellular messenger for autocrine and paracrine signaling[1]. There are two families of receptors for extracellular nucleotides: P2X and Rabbit Polyclonal to NRIP2 P2Y. P2X receptors are ion channels activated by ATP which induce fast and non-selective inward currents of Na+and Ca2+[2]. P2Y receptors are GPCR activated by ATP, ADP, UTP or UDP[3]. To date, seven mammalian P2X subtypes (P2X1-7) and eight mammalian P2Y subtypes (P2Y1,2,4,6,11,12,13,14) have been cloned and pharmacologically characterized[2][4]. ATP has been described as a regulator of inflammation, in embryonic and stem cell development, in ischemia and in several other processes[5][6]. In skeletal muscle, ATP has been implicated in the regulation of proliferation, differentiation and regeneration[7][8]and also in promoting the stabilization of the neuromuscular junction[9]. We have described that ATP is released trough Pannexin-1 (Panx1) channels by muscle cells after electrical stimulation and plays a crucial role in the activation of signaling pathways that lead to transcription of several genes[10][11]. Moreover, in adult muscle fibers, this signaling pathway mediates some of the muscle effects of nerve activity related with the process of muscle cell plasticity[11][12]. A number of skeletal muscle pathologies have been associated with alterations in the metabolism of extracellular ATP, with changes in the sensitivity towards ATP and with altered expression of purinergic receptors. One of them is the Duchene Muscular Dystrophy (DMD)[13][14], that is caused by the absence of functional dystrophin[15], a cytoskeleton protein mainly expressed near the cytosolic face of the plasma membrane[16]. In normal skeletal muscle, dystrophin is associated with a complex of glycoproteins known as dystrophin-associated proteins (DAPs), providing a linkage between the extracellular matrix and cytoskeleton[17]. Lack of dystrophin in dystrophic muscle results in loss of the complex integrity and allegedly impairs the Isochlorogenic acid B stability of the plasma membrane causing mechanical stress fragility and an increase in Ca2+permeability[18]. Nevertheless, the pathophysiology of this muscular dystrophy cannot be explained by this increased mechanical fragility alone and a role for dystrophin and DAPs has been suggested as part of a protein signaling complex involved in cell survival[19]. Several evidences relate ATP signaling with the abnormal Ca2+homeostasis observed in dystrophic muscle, suggesting an important role in the pathogenesis of this disease[13][14]. In myoblasts of a dystrophin-negative muscle cell line, exposure to extracellular ATP elicited a strong increase in cytoplasmic Ca2+concentrations, compared to control myoblasts. This increased susceptibility to ATP was due to changes in expression and function of P2X receptors and proposed to be a significant contributor to pathogenic Ca2+entry in dystrophic mouse muscle[13]. Also, the stimulation of P2 receptors with ATP continuously released in response to stretching has been proposed to constitutively activate the plasma membrane Na+/H+exchanger (NHE), contributing to the sustained increase in intracellular Ca2+[14]. Necrosis is probably a major contributor to muscle fiber loss in DMD and there is extensive experimental support for necrotic cell death in dystrophin-deficient muscles[20][23]. Nevertheless, several studies suggest that during the phase of acute muscle degeneration in the mdx mouse, apoptosis precedes necrosis[24]..