title: The roles of P(2X1)and P(2T AC)receptors in ADP-evoked calcium signalling in human platelets.
abstract: The roles of P(2X1)and P(2T AC)receptors in ADP-evoked Ca(2+)signalling were investigated in fura-2-loaded human platelets. Desensitization of the P(2X1)receptor with the selective agonist, alphabeta-methylene ATP, reduced the integral of the ADP-evoked rise in [Ca(2+)](i)to about 90% of control; a reduction equivalent to the integral of the P(2X1)-evoked response alone. After elevating cAMP or cGMP levels using prostaglandin E(1)or sodium nitroprusside, prior P(2X1)desensitization reduced the integral of the ADP-evoked response to about 70% of control. This reduction was greater than the integral of the P(2X1)-evoked response alone under the same conditions, suggesting rapidly activated Ca(2+)entry via the P(2X1)receptor potentiates Ca(2+)responses evoked via the phospholipase C-coupled P(2Y1)receptor. The P(2T AC)receptor antagonist, AR-C69931MX, at a concentration completely inhibiting aggregation, did not significantly affect the initial peaks but caused a significant reduction in the integrals of the ADP-evoked rises in [Ca(2+)](i)to about 71% or 77% of controls in the presence or absence of external Ca(2+)respectively. This suggests that the main effect of lowering cAMP levels after inhibition of adenylyl cyclase via P(2T AC)receptors may be reduced Ca(2+)removal from the cytosol. These results indicate that both the P(2X1)and P(2T AC)receptors play a significant role in ADP-evoked Ca(2+)signalling in human platelets.
authors.affiliation: Department of Physiology, University of Cambridge, Cambridge, UK. sos10@cam.ac.uk
authors.forename: S O
authors.initials: SO
authors.lastname: Sage
authors.forename: E H
authors.initials: EH
authors.lastname: Yamoah
authors.forename: J W
authors.initials: JW
authors.lastname: Heemskerk
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D006801:Humans; D008565:Membrane Proteins; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058469:Receptors, Purinergic P2X; D058925:Receptors, Purinergic P2Y12
chemical_list: D008565:Membrane Proteins; C548576:P2RY12 protein, human; D010975:Platelet Aggregation Inhibitors; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D058925:Receptors, Purinergic P2Y12; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; C117446:cangrelor; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate