Analysis of the influence of nucleotidases on the apparent activity of exogenous ATP and ADP at P2Y1 receptors.
1. ADP is a potent agonist of rat and human P2Y1 purinoceptors. ATP is a weak competitive antagonist. This study analyses the situation in which P2Y1 receptors are exposed to ATP in the presence of exogenous ecto-nucleotidases (apyrases) that have high or low ATPase/ADPase activity ratio. 2. Rat brain capillary endothelial cells of the B10 clone express P2Y1 receptors that couple to intracellular Ca2+ mobilization. They have low endogenous ecto-ATPase and ecto-ADPase activities. 3. ATP did not raise intracellular Ca2+ in B10 cells. Addition of apyrases III or VII (1 u ml(-1)) to ATP treated cells induced large intracellular Ca2+ transients. Apyrases had no action in the absence of ATP. 4. A 1 u ml(-1) apyrase III solution generated 20 microM ADP from 0.1 mM ATP within 15 s. This concentration of ADP was sufficient to produce maximal activation of P2Y1 receptors. 5. ATP was a full agonist of P2Y1 receptors in the presence of 1 u ml(-1) apyrase III. Dose response curves for the apparent actions of ATP were bell shaped in the presence of 0.1 u ml(-1) apyrase III. Apyrase III did not alter ADP dose response curves when coincubated with ADP for 15 s. 6. Apyrase VII (1 u ml(-1)) shifted dose response curves for the actions of ADP to larger concentrations. It induced a bell shaped ATP dose response curve. 7. Results suggest that ATPDases prevent P2Y1 receptor activation by degrading ADP but may contribute to P2Y1 receptor activation by generating ADP from ATP.
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Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Université de Nice-Sophia Antipolis, Valbonne, France.
Breittmayer
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JP
Frelin
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D000244:Adenosine Diphosphate / Q000096:biosynthesis* / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology; D009708:Nucleotidases / Q000494:pharmacology*; D058910:Purinergic P2 Receptor Agonists; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000187:drug effects*; D058472:Receptors, Purinergic P2Y1
C546382:P2RY1 protein, human; C546384:P2ry1 protein, rat; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009708:Nucleotidases; D000251:Adenosine Triphosphatases