Effect of extracellular ATP on cytosolic Ca2+ concentration in rat pulmonary artery myocytes.
Changes in cytosolic free Ca2+ concentration ([Ca2+]i) induced by ATP and other P2 purinoceptor agonists were investigated using indo 1 microspectrofluorimetry in single smooth muscle cells of the rat pulmonary artery. ATP (100 microM, 30 s) induced 3-4 cyclic rises in [Ca2+]i of decreasing amplitude. The first peak reached 743 +/- 24 nM from the resting value of 103 +/- 5 nM (n = 86). In approximately 50% of the cells, the ATP-induced [Ca2+]i oscillations were accompanied by a small but maintained rise in [Ca2+]i. In a series of 10 cells, the amplitude of this rise averaged 41 +/- 9 nM. The small rise 1) was also induced by 2-methylthio-ATP (2-MeS-ATP) and alpha,beta-methylene-ATP (alpha,beta-MeATP), 2) was insensitive to thapsigargin (TG, 1 microM), and 3) was abolished by the removal of external Ca2+. ATP-induced [Ca2+]i oscillations 1) were not abolished in the absence of external Ca2+, 2) were suppressed by treatment of the cells with TG (1 microM), and 3) were mimicked by UTP but not by 2-MeS-ATP or alpha,beta-MeATP. Both the number of cells that responded by [Ca2+]i oscillations and the maximal amplitude of the response depended on the agonist (ATP or UTP) concentration. The ATP-induced [Ca2+]i oscillations were not modified by tetracaine (500 microM) but were inhibited by forskolin (1 microM) and by phorbol 12,13-dibutyrate (PDB, 0.03 microM). The effect of PDB was reversed by the protein kinase C antagonist calphostin C (0.01 microM). These results suggest that the ATP-induced [Ca2+]i rise is mediated by the activation of P2x and P2u purinoceptors. Ca2+ entry through the P2x receptor channels produces a small and maintained [Ca2+]i rise. [Ca2+]i rise. Stimulation of P2u purinoceptor induces [Ca2+]i oscillations due to cyclic Ca2+ release from intracellular stores through inositol trisphosphate receptor channels.
Guibert
C
C
Laboratoire de Physiologie Cellulaire Respiratoire, Faculté de Médecine Victor Pachon, Université Bordeaux, France.
Pacaud
P
P
Loirand
G
G
Marthan
R
R
Savineau
J P
JP
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011651:Pulmonary Artery / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D000255:Adenosine Triphosphate; D002118:Calcium