Leukotrienes in the cardiovascular system.

Data are not yet available for ATP, but using thrombin as an agonist it has been shown that the initial transient rise in [Ca2+Ii is both necessary and sufficient to account for PGI, release (Hallam et al., 1988). ATP, like thrombin, also opens receptor-operated Ca? +-selective channels in endothelial cells (Hallam & Pearson, 1986) and these may be more important for EDRF production. Similar ATP-induced ion channels (demonstrated by patch-clamp studies) and inositol phosphate accumulation have been found in aortic smooth muscle cells (Benham & Tsien, 1987; Phaneuf et al., 1987), but it is not yet known whether these relate to P2.x or Pz.y purinoceptor occupation.