The activation of the A BR

The activation of the A2BR subtype triggers different intracellular metabolic pathways, often linked to the activation of adenylyl cyclase and increased levels of intracellular cAMP (Lynge et al., 2003, Bernareggi et al., 2015). The nAChR-channel Carmofur mediated by the cAMP/PKA pathway was reported to promote an increase in the open probability and duration of the nAChR-channel (Ferrer-Montiel et al., 1991, Lu et al., 1993). Here we found that the adenylyl cyclase activity is required for the modulatory effect on the nAChR channel activity, indicating cAMP as the key-signaling molecule responsible for the effect mediated by A2BRs. It has been already shown that the cAMP/PKA pathway is involved in trafficking, clustering and stability of the nAChR on the membrane surface (Reynolds et al., 2008, Martinez-Pena y Valenzuela et al., 2013; see also Berdeaux and Stewart, 2012). The current study suggests that in addition to possible functions related to the stability of nAChRs at the endplate region, the activation of A2BRs by adenosine and the downstream signaling, could be implicated in the control of the nAChR channel activity. Taking into account the crucial role of nAChRs at the NMJ, the adenosine-mediated modulation of the nAChR activity via A2BRs discloses a novel potential functional effect of the nucleoside on the regulation of synaptic transmission. Synaptic adenosine could be generated due to the breakdown of ATP (Ribeiro and Sebastião, 1987, Redman and Silinsky, 1994) co-released with ACh from motor nerve endings (Silinsky and Redman, 1996). Notably, both ATP and adenosine can inhibit transmitter release (Giniatullin and Sokolova, 1998), which is the major modulatory effect of these two purines. Given that ATP acts via excitatory P2Y1 (Choi et al., 2001) or P2Y2 receptors (Buvinic et al., 2009) at the postsynaptic level, the current study suggests that adenosine might act in concert with the parent compound ATP at the skeletal muscle level.