Adenosine - A Physiological Regulator and a Distress Signal

Abstract: The present brief review argues the case that adenosine can be both a distress signal and a physiological regula-tor. A key factor in determining which of these possibilities pertain is related to the number of receptors expressed. As the signaling from the adenosine receptor to the functional response generally involves amplification, we have a situation in-volving so called spare receptors. This has the consequence that alterations in the receptor number lead to shifts in the po-tency of the endogenous agonist rather than a shift in the maximum response elicited. The roles of adenosine are studied by antagonists and/or animals (mostly mice) with targeted deletions of receptors or enzymes involved in adenosine me-tabolism. Whereas, adaptive changes in the genetically modified mice can occur for the physiologically important effects, such adaptive changes are less likely to occur for the situations when adenosine acts as a distress signal. Keywords: Adenosine receptors, ATP, genetically modified mice, receptor reserve. There are four evolutionarily well conserved receptors for adenosine denoted A