Electrophysiological Consequences of Purinergic Receptor Stimulation in Isolated Rat Pulmonary Arterial Myocytes

Abstract

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 periodic oscillations of current were due primarily to a Ca(2+)-activated Cl- current (ICl,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) > > 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 ICl,Ca was UTP = ATP > > ADP > or = 2-meSATP > alpha,beta-meATP = adenosine. Both the fast transient inward current and ICl,Ca evoked by ATP and its analogues were abolished by the nonselective P2 purinoceptor antagonist suramin. These results show the existence of P2x and P2U purinoceptor subtypes in pulmonary arterial smooth muscle cells. Stimulation of these receptors results in activation of a fast transient inward cation current and ICl,Ca, respectively. It is likely that ATP acts via these receptor subtypes to regulate pulmonary arterial tone under physiological or pathological conditions.

Release of Ca2+ from the sarcoplasmic reticulum increases mitochondrial [Ca2+] in rat pulmonary artery smooth muscle cells

“…5A and C). When the membrane potential was clamped at −60 mV, ATP activated an inward current similar to that described by Hartley & Kozlowski (1997) for these cells, and therefore presumed to be a Ca¥-activated Cl¦ current. The peak value for this inward current was 207 ± 53 pA.…”

P2X Receptor Immunoreactivity in Different Arteries from the Femoral, Pulmonary, Cerebral, Coronary and Renal Circulations

“…In the majority of arteries, including ear, cerebral, mesenteric, pulmonary and coronary arteries, the desensitising nature of P2X receptor-mediated currents [21, 23, 43, 44, 45]and the sensitivity of contractile responses to the agonist α,β-meATP (EC 50 approximately 1 µ M ) [3, 23, 30, 41, 46, 47, 48]are indistinguishable from the properties of recombinant homomeric P2X 1 receptors [49]. There is no evidence to suggest that homomeric P2X 4 and P2X 5 or heteromeric P2X 1/5 receptors contribute to P2X receptor currents in arteries, as a characteristic property of these recombinant receptors are non-desensitising components to the P2X receptor currents [26, 50, 51, 52].…”

Purinergic Signaling in the Airways

“…Vasoconstriction of the rat pulmonary vascular bed by UTP and ATP is resistant to suramin antagonism (Rubino and Burnstock, 1996) and is probably mediated by P2Y 4 receptors. ATPand ADP-induced increase in [Ca 2ϩ ] i in rat pulmonary artery myocytes was found to be mediated by P2X and P2U (P2Y 2 and/or P2Y 4 ) receptors (Guibert et al, 1996;Hartley and Kozlowski, 1997). In endothelium-denuded rat pulmonary arteries, P2Y 2 and a UDP-sensitive receptor (presumably P2Y 6 ) were identified on myocytes (Hartley et al, 1998).…”