Effect of extracellular atp on cytosolic [ca2+] concentration in
rat pulmonary artery myocytes.
Guibert, Christelle, Pierre Pacaud, Gervaise Loirand, Roger Marthan,
and Jean-Pierre Savineau.
Laboratoire de Physiologie Cellulaire Respiratoire, Facult[acute]e
de M[acute]edecine Victor Pachon, Universit[acute]e Bordeaux 2,
Bordeaux, France
APStracts 3:0094L, 1996.
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 [mu]M, 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-MeSATP) and [alpha],[beta]
-methylene-ATP ([alpha],[beta]-MeATP) ; 2) was insensitive to
thapsigargin (TG, 1 [mu]M) 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 [mu]M) and 3) were mimicked by UTP
but not by 2-MeSATP 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
[mu]M) but were inhibited by forskolin (1 [mu]M) and by phorbol
12,13-dibutyrate (PDB, 0.03 [mu]M). The effect of PDB was reversed by
the protein kinase C antagonist calphostin C (0.01 [mu]M). 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.
Stimulation of P2U-purinoceptor induces [Ca2+]i oscillations due to
cyclic Ca2+ release from intracellular stores through InsP3 receptor
-channels.
Received 13 February 1996; accepted in final form 23 May 1996.
APS Manuscript Number L47-6.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96