Platelets and Purinergic receptors:
The major class of receptors present over platelets is the purinergic
receptors. They are of three subtypes P2Y1, P2Y12 and P2X1. The first
two are G-Protein coupled receptors and the last one is Adenosine gated
ion channel receptor. ADP is the physiological activator of platelets
that mediate its effects via these receptors. P2Y1 is Gq coupled that
act through phospholipase c system and P2Y12 is Gαi coupled that act by
adenyl cyclase system [4]. P2X1 acts via influx of calcium
functionally they produce only conformational changes in the platelets
along with synergistic action with other 2 receptors [5]. There are
several drugs that target these receptors. P2Y12 is the major receptor
involved in activation of GPIIb/IIIa receptors This is blocked by a
group of drugs called non-thienopyridines namely elinogrel, ticagrelor
and cangrelor [6]. Other than these there are various drugs that
target various other pathways of platelet aggregation, one among them is
the class called ADP inhibitors. They act by inhibiting ADP which is the
physiological activator of platelets. The drugs include clopidogrel and
prasugrel [6]. So, the purinergic receptors not only play an
important role in physiological homeostasis of platelets but also serve
as important drug targets for treating various life threatening and
common diseases. These antiplatelet drugs are one of the most common
drugs used in clinical practice. These antiplatelet drugs are used in
prophylaxis of various hypercoagulable states including Myocardial
infarction and atherosclerosis. Clopidogrel is used along with
atorvastatin and aspirin as loading dose in Myocardial infarction. This
strategy is known to reduce the development of reinfarction
substantially and provides benefits in patients with MI undoubtedly
[7].