Activation of receptor-operated cation channels via P2X1 not P2T purinoceptors in human platelets.
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.
MacKenzie
A B
AB
Physiological Laboratory, Downing Street, Cambridge, CB2 3EG, United Kingdom.
Mahaut-Smith
M P
MP
Sage
S O
SO
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
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