P2Y receptor‐mediated Ca2+ signalling in cultured rat aortic smooth muscle cells

ATP, UTP, ADP and ADP‐β‐S elicited Ca2+‐signals in cultured aortic smooth muscle cells although ADP, UDP and ADP‐β‐S gave ∼40% of the maximal response seen with ATP and UTP. Adenosine, AMP or α,β‐methylene‐ATP had no effect. These responses were attributed to P2Y2/4 and P2Y1 receptors, which we assumed could be selectively activated by UTP and ADP‐β‐S respectively. The response to UTP was reduced (∼50%) by pertussis toxin, whilst this toxin had no effect upon the response to ADP‐β‐S. This suggests P2Y2/4 receptors simultaneously couple to pertussis toxin‐sensitive and ‐resistant G proteins whilst P2Y1 receptors couple to only the toxin‐resistant proteins. Repeated stimulation with UTP or ADP‐β‐S caused desensitization which was potentiated by 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA) and attenuated by staurosporine. TPA completely abolished sensitivity to ADP‐β‐S but the response to UTP had a TPA‐resistant component. In pertussis toxin‐treated cells, however, TPA could completely abolish sensitivity to UTP and so the TPA‐resistant part of this response seems to be mediated by pertussis toxin‐sensitive G proteins. Loss of sensitivity to UTP did not occur when pertussis toxin‐treated cells were repeatedly stimulated with this nucleotide, suggesting that pertussis toxin‐sensitive G proteins mediate this effect. The toxin did not, however affect desensitization to ADP‐β‐S. British Journal of Pharmacology (1999) 126, 1660–1666; doi:10.1038/sj.bjp.0702470