title: Activation of receptor-operated cation channels via P2X1 not P2T purinoceptors in human platelets.
abstract: We have investigated the purinoceptor subtypes responsible for calcium signaling in human platelets, which previous studies have shown to involve both Ca2+ influx via receptor-operated cation channels and release of Ca2+ from intracellular stores. Fura-2 measurements of [Ca2+]i in stirred platelet suspensions showed that both ADP (40 microM) and the non-hydrolyzable ATP analogue alphabeta-meATP (alpha, beta-methyleneadenosine 5-triphosphate, 10 microM) activated a rapid Ca2+ influx whereas only ADP mobilized Ca2+ from internal stores. In "nystatin" whole-cell patch clamp recordings, ATP, ADP, and the non-hydrolyzable ATP analogues, alpha, beta-meATP and ATPgammaS (adenosine 5 -O-(3-thiotriphosphate), all activated a cation channel permeable to both monovalent and divalent cations with a single-channel conductance of 11 picosiemens in NaCl saline. The current response to ATP (40 microM) was activated within 20 ms and desensitized with a time constant of 47-107 ms in the continued presence of agonist, which are characteristics of P2X1 receptors in other tissues. We conclude that human platelets possess a P2X1 purinoceptor, which mediates a rapid phase of ADP- or ATP-evoked Ca2+ entry via a cation channel, whereas one or more separate ADP-selective P2 purinoceptors evoke release of calcium from intracellular stores.
authors.affiliation: Physiological Laboratory, Downing Street, Cambridge, CB2 3EG, United Kingdom.
authors.forename: A B
authors.initials: AB
authors.lastname: MacKenzie
authors.forename: M P
authors.initials: MP
authors.lastname: Mahaut-Smith
authors.forename: S O
authors.initials: SO
authors.lastname: Sage
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D001081:Apyrase / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology; D001792:Blood Platelets / Q000502:physiology*; D002118:Calcium / Q000097:blood*; D015220:Calcium Channels / Q000097:blood*; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins; D018408:Patch-Clamp Techniques; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D058469:Receptors, Purinergic P2X; D058925:Receptors, Purinergic P2Y12
chemical_list: D015220:Calcium Channels; D005456:Fluorescent Dyes; D008565:Membrane Proteins; C548576:P2RY12 protein, human; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D058925:Receptors, Purinergic P2Y12; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D001081:Apyrase; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D001241:Aspirin; D002118:Calcium; D016257:Fura-2