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Multiple P2 Receptors Contribute to a Transient Increase in Intracellular Ca 2+ Concentration in Atp‐Stimulated Rat Brown Adipocytes
Author(s) -
OmatsuKanbe Mariko,
Isono Takahiro,
Matsuura Hiroshi
Publication year - 2002
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/eph8702455
Subject(s) - ppads , suramin , extracellular , thapsigargin , intracellular , receptor , p2 receptor , medicine , endocrinology , agonist , chemistry , biology , purinergic receptor , biophysics , biochemistry
Extracellular ATP in micromolar concentrations evokes a transient elevation in intracellular free Ca 2+ concentration ([Ca 2+ ] i ), which arises primarily from a release of Ca 2+ from intracellular stores in rat brown adipocytes. We investigated the mechanisms underlying this transient nature of [Ca 2+ ] i elevation during exposure to ATP by using fura‐2 fluorescence measurements together with the P2 receptor antagonists pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulfonic acid (PPADS) and suramin. Extracellular ATP (10 μM) almost completely depressed the thapsigargin (100 nM)‐evoked [Ca 2+ ] i elevation mediated through store‐operated Ca 2+ entry. The inhibitory effect of ATP was antagonized by PPADS with IC 50 of 0.7 μM. In the presence of PPADS at concentrations of more than 5 μM, the ATP‐induced [Ca 2+ ] i elevation became sustained during the entire duration of the agonist application, although the magnitude of the sustained [Ca 2+ ] i elevation was reduced in a concentration‐dependent manner by PPADS with an IC 50 of 200 μM. In contrast, the ATP‐induced [Ca 2+ ] i elevation was blocked by suramin in a concentration range similar to that required to antagonize the inhibitory effect of ATP on the store‐operated pathway. These results suggest that the [Ca 2+ ] i responses to extracellular ATP in rat brown adipocytes are mediated through the activation of at least two distinct P2 receptors exhibiting different sensitivities to PPADS but similar sensitivities to suramin. Extracellular ATP stimulates the PPADS‐resistant P2 receptor to mobilize intracellular Ca 2+ stores, which is probably followed by the activation of store‐operated Ca 2+ entry. Extracellular ATP, however, would inhibit this Ca 2+ entry process through the stimulation of the PPADS‐sensitive P2‐receptor, which may underlie the transient nature of [Ca 2+ ] i elevation in response to extracellular ATP.