title: The T-tubule membrane ATP-operated P2X4 receptor influences contractility of skeletal muscle.
abstract: Evidence indicates that extracellular ATP may have relevant functions in skeletal muscle, even though the physiological role and distribution of specific signaling pathway elements are not well known. The present work shows that P2X4 receptor, an extracellular ATP-regulated cell membrane channel permeable to Ca2+, is expressed in several tissues of the rat, including skeletal muscle. A specific antibody detected a protein band of approximately 60 kDa. Immunofluorescence demonstrated that P2X4 has an intracellular localization, and confocal analysis revealed that the receptor colocalizes with the T-tubule membrane DHP receptor. Considering that the natural agonist of P2X4 is ATP, we explored if changes of extracellular ATP levels could occur in contracting skeletal muscle to regulate the channel. In vitro experiments showed that substantial ATP is released and rapidly hydrolyzed after electrical stimulation of rat muscle fibers. Results show that the presence of ATP-degrading enzymes (hexokinase/apyrase), inhibitors of P2X receptors or Ca2+-free conditions, all abolished the progressive twitch tension potentiation produced in soleus muscle by low-frequency (0.05 Hz) stimulation. These data reveal that ATP-mediated Ca2+ entry, most likely through P2X4 receptor, may play an important role in modulating the contractility of skeletal muscle.
authors.affiliation: Department of Biomedical and Experimental Sciences, University of Padova, Padova, Italy.
authors.forename: Dorianna
authors.initials: D
authors.lastname: Sandonà
authors.forename: Daniela
authors.initials: D
authors.lastname: Danieli-Betto
authors.forename: Elena
authors.initials: E
authors.lastname: Germinario
authors.forename: Donatella
authors.initials: D
authors.lastname: Biral
authors.forename: Tiziana
authors.initials: T
authors.lastname: Martinello
authors.forename: Antonella
authors.initials: A
authors.lastname: Lioy
authors.forename: Elena
authors.initials: E
authors.lastname: Tarricone
authors.forename: Stefano
authors.initials: S
authors.lastname: Gastaldello
authors.forename: Romeo
authors.initials: R
authors.lastname: Betto
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D007425:Intracellular Membranes / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D058848:Receptors, Purinergic P2X4; D015398:Signal Transduction
chemical_list: C548228:P2rx4 protein, rat; D012333:RNA, Messenger; D018048:Receptors, Purinergic P2; D058848:Receptors, Purinergic P2X4; D000255:Adenosine Triphosphate; D002118:Calcium