Adenosine, antagonists, ATP
Adenosine is a nucleoside which activates purinergic receptors of P1type, generally called A1, A2 and A3 receptors while nucleotides such as ATP activate purinergic receptors of P2 type.
Adenosine is an endogenous nucleoside, present in all the cells of the body.
Adenosine results from the hydrolysis of adenosine monophosphate, AMP, catalyzed by a 5-nucleotidase, an intra and extracellular enzyme, and from the hydrolysis of adenosylhomocysteine.
Adenosine is transformed into:
- inosine by adenosine deaminase, then inosine into hypoxanthine under the influence of a purine nucleoside phosphorylase. The inhibition of adenosine deaminase tends to increase adenosine concentration.
- adenosine monophosphate (AMP) by an ATP-dependant adenosine kinase.
The mechanisms of adenosine release as a neuromodulator in the central nervous system are not well known.
During ischemia, adenosine is released from AMP by cytoplasmic and membrane nucleotidases.
Adenosine released into plasma has an extremely short half-life, approximately one second, because, in addition to its metabolic biotransformations, it is taken up by erythrocytes. Effects remote from its sites of release are thus not very probable.
Adenosine and Adenosine triphosphate (ATP)