Ischemic skeletal muscle protection by direct delivery of ATP – the role of purinergic and adenosine receptors

Abstract

Fusogenic Lipid vesicles loaded with ATP (FLVs‐ATP) have been used to conserve critical levels of intracellular ATP to minimize tissue damage in ischemia/reperfusion injury. Although beneficial its precise mechanism was unclear. The purpose of this study was to determine the role of purinergic and adenosine receptors during ATP delivery to ischemic skeletal muscles. We hypothesized that the ATP from FLVs‐ATP activates purinergic and adenosine receptors on cells, and has an ATP sparing effect. We used phosphocreatine (PCr) half life as an index of internal depletion of ATP in order to distinguish between intracellular and extracellular ATP (FLVs‐ATP). Extensor Digitorum Longus muscles (n=10/group) were perfused: Heparinized Lactated Ringer's (HLR); Free ATP; ATPgamma; Adenosine; FLVs; FLVs‐ATP; FLVs‐ATP + purinergic blocker; FLVs‐ATP + adenosine blockers. 31 Phosphate Nuclear Magnetic Resonance was used to measure PCr levels and calculate its half life. We found that FLVs‐ATP with purinergic receptor blockers was beneficial illustrating that purinergic receptors may have played a minor/no role in prolonging the PCr half life. In contrast FLVs‐ATP + adenosine receptors blockers showed significant difference compared to purinergic blockers in the PCr half life (p<0.05) but not significant to HLR indicating that the beneficial effects of exogenous ATP are being mediated by adenosine receptors.