Intracellular recordings were made from the circular smooth muscle cells of
the canine jejunum to study the effect of exogenous ATP and to compare the
ATP response to the nonadrenergic, noncholinergic (NANC) inhibitory juncti
on potential (IJP) evoked by electrical field stimulation (EFS). Under NANC
conditions, exogenous ATP evoked a transient hyperpolarization (6.5 +/- 0.
6 mV) and EFS evoked a NANC IJP (17 +/- 0.4 mV). omega-Conotoxin GVIA (100
nM) and a low-Ca2+, high-Mg2+ solution abolished the NANC IJP but had no ef
fect on the ATP-evoked hyperpolarization. The ATP-evoked hyperpolarization
and the NANC IJP were abolished by apamin (1 mu M) and N-G-nitro-L-arginine
(100 mu M). Oxyhemoglobin (5 mu M) partially (38.8 +/- 5.5%) reduced the a
mplitude of the NANC IJP but had no effect on the ATP-evoked hyperpolarizat
ion. Neither the NANC IJP nor the ATP-evoked hyperpolarization was affected
by P2 receptor antagonists or agonists, including suramin, reactive blue 2
, 1-(N,O-bis-[5-isoquinolinesulfonyl]-N-methyl-L-tyrosyl)-4-phenylpiperazin
e, pyridoxal phosphate-6-azopheny1-2',4'-disulfonic acid, alpha,beta-methyl
ene ATP, 2-methylthioadenosine 5'-triphosphate tetrasodium salt, and adenos
ine 5'-O-2-thiodiphosphate. The data suggest that ATP evoked an apamin-sens
itive hyperpolarization in circular smooth muscle cells of the canine jejun
um via local production of NO in a postsynaptic target cell.