Heterogeneous calcium responses to extracellular ATP in cultured rat renaltubule cells

There is increasing evidence that extracellular ATP acting on purinoceptors may play an important signalling role in renal epithelial cells, often thr ough alterations in cellular Ca2+. In this paper effects of extracellular A TP and related purinoceptor agonists and antagonists on [Ca2+](i) have been studied in single cells from primary cultures of rat proximal tubule cells . Responses to 1-100 mu mol/l ATP were heterogeneous; 55% of cells showed a transient rise in [Ca2+](i), 20% of cells showed a transient fall; in 25% there was no response. ATP actions on [Ca2+](i) were abolished by pre-treat ment with thapsigargin. The P-2 receptor antagonist suramin unexpectedly in creased the [Ca2+](i) response to ATP; the related antagonist XAMR 0721 did not significantly alter ATP responses. This difference is likely to arise from the inhibition of ATP hydrolysis by suramin. UTP, ADP and the non-hydr olyzable ATP analogue adenosine-5'-O-(3-thio)-triphosphate (ATP gammaS)prod uced similar increases in [Ca2+](i). The magnitude of the [Ca2+](i) respons es to 100 mu mol/l agonist gave an agonist potency order of ATP greater tha n or equal to ADP greater than or equal to UTP approximate to ATP gammaS. D esensitisation experiments demonstrated the presence of mure than one P2Y A TP receptor subtype on a single cell. These results are consistent with the expression of purinoceptors of both P2Y(1) and P2Y(2) subclasses on indivi dual rat proximal tubule cells coupled to inositol trisphosphate-mediated r elease of intracellular calcium stores. (C) 2001 Elsevier Science B.V. All rights reserved.