Vol. 280, Issue 2, R519-R526, February 2001
Purine and pyrimidine nucleotide-sensitive phospholipase
A2 in ampulla from frog semicircular canal
Marie
Teixeira1,
Christian
Bernard2,
Evelyne
Ferrary1, and
Daniel
Butlen1
1 Institut National de la Santé et de la Recherche
Médicale, Unité 426, Faculté de Médecine
Xavier Bichat, 75870 Paris Cedex 18; and 2 Laboratoire de
Neurophysiologie Sensorielle, Université de Rouen, 76821 Mont-Saint-Aignan Cedex, France
This study was
attempted to characterize pharmacologically the P2Y receptors
triggering phospholipase A2 (PLA2) activation in ampulla from frog semicircular canal. A microassay was developed to
screen the abilities of UTP analogs to stimulate
[3H]arachidonic acid release by labeled ampullas. At
26°C UTP induced a dose-dependent and saturable increase of
PLA2 activity (apparent activation constant 1.3 ± 0.4 µM, Hill coefficient 0.9 ± 0.2, maximal stimulating factor
2.0 ± 0.1). The rank order of potency of agonists for
PLA2 activation was UTP 
UDP > adenosine
5'-O-(2-thiodiphosphate) = adenosine
5'-O-(3-thiotriphosphate) ATP = 2-methylthio-ATP ADP = diadenosine tetraphosphate 
,
-methylene-ATP = CTP > 2' and
3'-O-(4-benzoylbenzoyl)-ATP AMP = UMP >>
uridine and adenosine. UTP- and 2-methylthio-ATP-induced
PLA2 activations were inhibited by U-73122, GF-109203X, and
methyl arachidonyl fluorophosphate. Basal activity was stimulated by
phorbol ester and epinephrine and reduced by vasotocin, isoproterenol,
prostaglandin E2, cAMP, and forskolin. H-89 restored
the cAMP- and forskolin-inhibited PLA2 activities. Results
indicate that P2Y receptor-mediated PLA2 stimulation
requires phopholipase C and protein kinase C activations and basal
activity is inhibited by agonist-stimulated cAMP-dependent mechanisms.
inner ear; arachidonic acid release; P2Y receptors; UTP analogs
