Normal myotubes and adult innervated skeletal myofibers express the glycoprotein 
pannexin1 (Panx1). Six of them form a "gap junction hemichannel-like" structure 
that connects the cytoplasm with the extracellular space; here they will be 
called Panx1 channels. These are poorly selective channels permeable to ions, 
small metabolic substrate, and signaling molecules. So far little is known about 
the role of Panx1 channels in muscles but skeletal muscles of Panx1(-/-) mice do 
not show an evident phenotype. Innervated adult fast and slow skeletal myofibers 
show Panx1 reactivity in close proximity to dihydropyridine receptors in the 
sarcolemma of T-tubules. These Panx1 channels are activated by electrical 
stimulation and extracellular ATP. Panx1 channels play a relevant role in 
potentiation of muscle contraction because they allow release of ATP and uptake 
of glucose, two molecules required for this response. In support of this notion, 
the absence of Panx1 abrogates the potentiation of muscle contraction elicited 
by repetitive electrical stimulation, which is reversed by exogenously applied 
ATP. Phosphorylation of Panx1 Thr and Ser residues might be involved in Panx1 
channel activation since it is enhanced during potentiation of muscle 
contraction. Under denervation, Panx1 levels are upregulated and this partially 
explains the reduction in electrochemical gradient, however its absence does not 
prevent denervation-induced atrophy but prevents the higher oxidative state. 
Panx1 also forms functional channels at the cell surface of myotubes and their 
functional state has been associated with intracellular Ca(2+) signals and 
regulation of myotube plasticity evoked by electrical stimulation. We proposed 
that Panx1 channels participate as ATP channels and help to keep a normal 
oxidative state in skeletal muscles.