title: ATP released by electrical stimuli elicits calcium transients and gene expression in skeletal muscle.
abstract: ATP released from cells is known to activate plasma membrane P2X (ionotropic) or P2Y (metabotropic) receptors. In skeletal muscle cells, depolarizing stimuli induce both a fast calcium signal associated with contraction and a slow signal that regulates gene expression. Here we show that nucleotides released to the extracellular medium by electrical stimulation are partly involved in the fast component and are largely responsible for the slow signals. In rat skeletal myotubes, a tetanic stimulus (45 Hz, 400 1-ms pulses) rapidly increased extracellular levels of ATP, ADP, and AMP after 15 s to 3 min. Exogenous ATP induced an increase in intracellular free Ca(2+) concentration, with an EC(50) value of 7.8 +/- 3.1 microm. Exogenous ADP, UTP, and UDP also promoted calcium transients. Both fast and slow calcium signals evoked by tetanic stimulation were inhibited by either 100 mum suramin or 2 units/ml apyrase. Apyrase also reduced fast and slow calcium signals evoked by tetanus (45 Hz, 400 0.3-ms pulses) in isolated mouse adult skeletal fibers. A likely candidate for the ATP release pathway is the pannexin-1 hemichannel; its blockers inhibited both calcium transients and ATP release. The dihydropyridine receptor co-precipitated with both the P2Y(2) receptor and pannexin-1. As reported previously for electrical stimulation, 500 mum ATP significantly increased mRNA expression for both c-fos and interleukin 6. Our results suggest that nucleotides released during skeletal muscle activity through pannexin-1 hemichannels act through P2X and P2Y receptors to modulate both Ca(2+) homeostasis and muscle physiology.
authors.affiliation: Centro de Estudios Moleculares de la Célula, Facultad de Medicina, Instituto de Ciencias Biomédicas, Universidad de Chile, Casilla 70005, Santiago 7, Chile.
authors.forename: Sonja
authors.initials: S
authors.lastname: Buvinic
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Almarza
authors.forename: Mario
authors.initials: M
authors.lastname: Bustamante
authors.forename: Mariana
authors.initials: M
authors.lastname: Casas
authors.forename: Javiera
authors.initials: J
authors.lastname: López
authors.forename: Manuel
authors.initials: M
authors.lastname: Riquelme
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Sáez
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Huidobro-Toro
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001081:Apyrase / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D017630:Connexins / Q000235:genetics / Q000378:metabolism; D004558:Electric Stimulation; D015870:Gene Expression; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D011189:Potassium Chloride / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology
chemical_list: D020746:Calcium Channels, L-Type; D017630:Connexins; D015850:Interleukin-6; D009419:Nerve Tissue Proteins; C503631:Panx1 protein, mouse; D020033:Protein Isoforms; D016760:Proto-Oncogene Proteins c-fos; D018048:Receptors, Purinergic P2; D019837:Ryanodine Receptor Calcium Release Channel; C479936:pannexin 1, rat; D013498:Suramin; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D001081:Apyrase; D002118:Calcium