Multiple Motor Effects of ATP and their Inhibition by P₂ Purinoceptor Antagonist, Pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic Acid in the Small Intestine of the Guinea‐Pig

Abstract

Adenosine 5ø-triphosphate (ATP) may be an important neurotransmitter in the gastrointestinal tract. The present study examined the motor effects of exogenous ATP on longitudinally-oriented preparations of the guinea-pig isolated ileum and the influence of drugs on the ATP-induced responses. High micromolar concentrations of ATP caused two types of contraction, a phasic, cholinergic response and a tonic, tetrodotoxin-resistant contraction. The phasic contraction was reduced by hexamethonium (5¿10 ª5 M), but left uninfluenced by capsaicin tachyphylaxis or tachyphylaxis to a,bmethylene ATP. The tonic response was resistant to atropine, hexamethonium, capsaicin, w-conotoxin GVIA, or pretreatment with a,b-methylene ATP. Both types of ATP-induced contraction were diminished or abolished by the P 2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2ø,4ø-disulphonic acid (PPADS, 3¿10ª6 and 3¿10 ª5 M, respectively). In the precontracted, atropine-treated ileum ATP (10 ª6 -10 ª4 M) caused guanethidine-resistant relaxation. This response was not influenced by tetrodotoxin, w-conotoxin GVIA, or N G -nitro-L-arginine, but was abolished by apamin (10 ª7 M), and inhibited by PPADS (3¿10 ª5 M) or reactive blue 2 (10 ª5 M), in a surmountable manner. A high degree of tachyphylaxis was observed with the relaxant effect of ATP (10 ª5 -10 ª4 M). A high concentration (3¿10 ª4 M) of PPADS failed to influence ileum contractions to exogenous acetylcholine or histamine. It is concluded that, in addition to its direct contractile action in the guinea-pig ileum, ATP can activate (partly preganglionic) cholinergic neurones, an effect whose mechanism is largely different from that of a,b-methylene ATP. ATP also causes relaxation by a direct, probably P 2Y -receptormediated effect on the smooth muscle. All motor effects of ATP are inhibited by the antagonist PPADS.

Relative contribution of ecto‐ATPase and ecto‐ATPDase pathways to the biphasic effect of ATP on acetylcholine release from myenteric motoneurons

“…In the myenteric plexus, all enteric neurons, except NO synthase (EC 1.14.13.39)‐immunoreactive inhibitory muscle motoneurons, contain choline acetyltransferase (EC 2.3.1.6) (Furness, 2000), suggesting that myenteric neurons are mostly cholinergic and that ATP and ACh might be co‐released. Here, we provided evidence indicating that cholinergic nerve terminals of the myenteric plexus of the rat ileum possess TNP‐ATP‐sensitive P2X receptors triggering the release of [ 3 H]ACh in the absence of action potential generation (see also Barthó et al. , 2006).…”

“…It has been reported that purinergic neurotransmission may be mediated by cholinergic neurons (Matsuo et al. , 1997; Barthó et al. , 2006).…”

Administration of exogenous adenosine triphosphate to ischemic skeletal muscle induces an energy-sparing effect: Role of adenosine receptors

“…[52-54] Thus, antagonism of both P2X and P2Y receptors by PPADS may explain the prolongation of PCr half-life observed in our study.…”

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca2+ release and SK channel activation

“…In particular, it is known that α,β-Me-ATP application leads to neural fiber-mediated cholinergic contractions [5] , and altered ATP release from cholinergic fibers in response to pre-junctional P2Y receptor activation may have occurred in our preparations [8] . Therefore, we examined the P2Y receptor-induced transient relaxation following preincubation with atropine, L-NAME or TTX and found that at least the P2Y receptor-mediated relaxation was independent of acetylcholine or nitric oxide release from pre-junctional nerve fibers.…”

“…While NO leads to a long-lasting inhibition of smooth muscle motility, the available data on purinergic responses are less consistent, as both excitatory and inhibitory effects have been observed and seem to depend on the subtype and cellular location of P2 purinoceptors. In addition, species differences should also be considered [2][3][4][5][6][7][8][9][10] . Seven cloned ionotropic P2X receptors that combine heteromerically, as well as eight cloned metabotropic P2Y receptors, account for the large heterogeneity of purinoceptormediated effects [11] .…”