Thank you for the comment. I believe Lock Macdonald has some answers to your questions too. (his name was not included in the author's list by mistake, and he submitted this paper). I agree with you that UTP/UDP should be released at least from platelets and act on the P2u receptors in smooth muscle cells from cerebral arteries. In our previous studies, we found P2u receptor in rat basilar smooth muscle and the calcium response is more pronounded to UTP/UDP than that of ATP. In isometric tension, dog basilar contracts two times more to UTP than ATP.