Electrophysiological consequences of purinergic receptor stimulation in isolated rat pulmonary arterial myocytes

Neither the electrophysiological effects of purinergic receptor stimulation nor the role of ATP in regulating the tone of pulmonary arterial smooth muscle has been determined. Therefore, we investigated the effects of purine nucleotides on acutely dissociated smooth muscle cells from rat small pulmonary arteries using the patch-clamp recording technique. Extracellular application of ATP activated a fast transient inward current (which decayed in the continued presence of the nucleotide) and produced sustained periodic oscillations of predominantly inward current. Pharmacological and anion substitution experiments revealed that the transient inward current was carried by the movement of cations. In contrast, the peri odic oscillations of current were due primarily to a Ca2+-activated Cl- current (I-Cl,I-Ca) dependent on the release of Ca2+ from intracellular stores. Experiments using ATP analogues revealed the following order of potency for activation of the fast transient inward current: 2-methylthio ATP (2-meSATP)>ATP>alpha,beta-methylene ATP (alpha,beta-meATP)much greater than ADP>UTP=adenosine. Cross desensitization was seen between applications of ATP, alpha,beta-meATP, and 2-meSATP, suggesting that these agonists act via a common site. The order of potency for activation of I-Ca,I-Cl was UTP=ATP much greater than ADP greater than or equal to 2-meSATP>alpha,beta-meATP=adenosine. Both the fast transient inward current and I-Cl,I-Ca evoked by ATP and its analogues were abolished by the nonselective P-2 purinoceptor antagonist suramin. These results show the existence of P-2X and P-2U purinoceptor subtypes in pulmonary arterial smooth muscle cells. Stimulation of these receptors results in activation of a fast transient inward cation current and I-Cl,I-Ca, respectively. It is likely that ATP acts via these receptor subtypes to regulate pulmonary arterial tone under physiological or pathological conditions.