Skeletal muscle expresses the extracellular cyclic AMP–adenosine pathway

Abstract

Background and purpose: cAMP is a key intracellular signalling molecule that regulates multiple processes of the vertebrate skeletal muscle. We have shown that cAMP can be actively pumped out from the skeletal muscle cell. Since in other tissues, cAMP efflux had been associated with extracellular generation of adenosine, in the present study we have assessed the fate of interstitial cAMP and the existence of an extracellular cAMP-adenosine signalling pathway in skeletal muscle. Experimental approach: cAMP efflux and/or its extracellular degradation were analysed by incubating rat cultured skeletal muscle with exogenous cAMP, forskolin or isoprenaline. cAMP and its metabolites were quantified by radioassay or HPLC, respectively. Key results: Incubation of cells with exogenous cAMP was followed by interstitial accumulation of 5 0 -AMP and adenosine, a phenomenon inhibited by selective inhibitors of ecto-phosphodiesterase (DPSPX) and ecto-nucleotidase (AMPCP). Activation of adenylyl cyclase (AC) in cultured cells with forskolin or isoprenaline increased cAMP efflux and extracellular generation of 5 0 -AMP and adenosine. Extracellular cAMP-adenosine pathway was also observed after direct and receptor-dependent stimulation of AC in rat extensor muscle ex vivo. These events were attenuated by probenecid, an inhibitor of ATP binding cassette family transporters. Conclusions and implications:Our results show the existence of an extracellular biochemical cascade that converts cAMP into adenosine. The functional relevance of this extracellular signalling system may involve a feedback modulation of cellular response initiated by several G protein-coupled receptor ligands, amplifying cAMP influence to a paracrine mode, through its metabolite, adenosine.

Cellular function and molecular structure of ecto-nucleotidases

“…GPC glycerophosphorylcholine, LPC lysophosphatidylcholine, pNPPC p-nitrophenyl phosphorylcholine, SPC sphingosylphosphorylcholine substrate [354][355][356][357]. There is ample evidence for the hydrolysis of extracellular cAMP by intact cells but the responsible enzyme has not been clearly identified [358,359]. Nucleoside monophosphates such as AMP or UMP are not hydrolyzed but exert competitive product inhibition of the NPP reaction [354,356,360,361].…”

Cardiac myocyte–secreted cAMP exerts paracrine action via adenosine receptor activation

“…Inspired by the early finding that systemic infusion of cAMP alters renal activity (8), exogenously added cAMP was shown to also elicit effects in various cells and tissues in vitro (25,26), yet the physiological relevance of the latter remained unresolved. We provide several lines of evidence that the myocardium as a sympathetically innervated organ can supply extracellular cAMP to establish a local paracrine signal: first, increased cAMP efflux was detected after Iso stimulation of primary CMs in vitro ( Figure 2A) and in the pericardial fluid of mice subjected to TAC (Supplemental Figure 3D).…”

Skeletal muscle contraction-induced vasodilator complement production is dependent on stimulus and contraction frequency

“…Diameter was measured before, during, and after 2 min of skeletal muscle contraction stimulated over a range of stimulus frequencies [4, 20, and 40 Hz; 15 contractions/min (cpm), 250 ms train duration] and a range of contraction frequencies (6,15, and 60 cpm; 20 Hz stimulus frequency, 250 ms train duration). Muscle fibers were stimulated in the absence and presence of an inhibitor of adenosine receptors [10 Ϫ6 M xanthine amine congener (XAC)], an ATP-dependent potassium (K ϩ ) channel inhibitor (10 Ϫ5 M glibenclamide), an inhibitor of a source of K ϩ by inhibition of voltage-dependent K ϩ channels [3 ϫ 10 Ϫ4 M 3,4-diaminopyridine (DAP)], and an inhibitor of nitric oxide synthase [10 Ϫ6 M N G -nitro-L-arginine methyl ester (L-NAME) ϩ 10 Ϫ7 S-nitroso-N-acetylpenicillamine (a nitric oxide donor)].…”

“…First published May 22, 2009 doi:10.1152/ajpheart.00216.2009.-To test the hypothesis that the vasodilator complement that produces arteriolar vasodilation during muscle contraction depends on both stimulus and contraction frequency, we stimulated four to five skeletal muscle fibers in the anesthetized hamster cremaster preparation in situ and measured the change in diameter of arterioles at a site of overlap with the stimulated muscle fibers. Diameter was measured before, during, and after 2 min of skeletal muscle contraction stimulated over a range of stimulus frequencies [4,20, and 40 Hz;15 …”