Participation of ATP in nonadrenergic, noncholinergic relaxation of longitudinal muscle of wistar rat jejunum

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca(2+) release and SK channel activation

AIM

Purinergic signaling plays a major role in the enteric nervous system, where it governs gut motility through a number of P2X and P2Y receptors. The aim of this study was to investigate the P2Y receptor-mediated motility in rat longitudinal ileum preparations.

METHODS

Ileum smooth muscle strips were prepared from rats, and fixed in an organ bath. Isometric contraction and relaxation responses of the muscle strips were measured with force transducers. Drugs were applied by adding of stock solutions to the organ bath to yield the individual final concentrations.

RESULTS

Application of the non-hydrolyzable P2 receptor agonists α,β-Me-ATP or 2-Me-S-ADP (10, 100 μmol/L) dose-dependently elicited a transient relaxation response followed by a sustained contraction. The relaxation response was largely blocked by SK channel blockers apamin (500 nmol/L) and UCL1684 (10 μmol/L), PLC inhibitor U73122 (100 μmol/L), IP3 receptor blocker 2-APB (100 μmol/L) or sarcoendoplasmic Ca(2+) ATPase inhibitor thapsigargin (1 μmol/L), but not affected by atropine, NO synthase blocker L-NAME or tetrodotoxin. Furthermore, α,β-Me-ATP-induced relaxation was suppressed by P2Y1 receptor antagonist MRS2179 (50 μmol/L) or P2Y13 receptor antagonist MRS2211 (100 μmol/L), and was abolished by co-application of the two antagonists, whereas 2-Me-S-ADP-induced relaxation was abolished by P2Y6 receptor antagonist MRS2578 (50 μmol/L). In addition, P2Y1 receptor antagonist MRS2500 (1 μmol/L) not only abolished α,β-Me-ATP-induced relaxation, but also suppressed 2-Me-S-ADP-induced relaxation.

CONCLUSION

P2Y receptor agonist-induced transient relaxation of rat ileum smooth muscle strips is mediated predominantly by P2Y1 receptor, but also by P2Y6 and P2Y13 receptors, and involves PLC, IP3, Ca(2+) release and SK channel activation, but is independent of acetylcholine and NO release.

Nitric oxide and carbon monoxide act as inhibitory neurotransmitters in the longitudinal muscle of C57BL/6J mouse distal colon

The present study was designed to identify the inhibitory neurotransmitters mediating nonadrenergic noncholinergic relaxation in the longitudinal muscle of C57/BL mouse distal colon. Relaxation induced by electrical field stimulation (EFS) was recorded isotonically in the presence of atropine and guanethidine. Cyclic guanosine-3',5'-monophosphate (cyclic GMP) content was measured by radioimmunoassay. EFS-induced relaxation was inhibited by nitro-L-arginine (L-NNA) and Sn (IV) protoporphyrin dichloride IX (SnPP-IX), a nitric oxide (NO) and carbon monoxide (CO) synthase inhibitor, respectively. A combination of both inhibitors produced an additive effect. ODQ, a soluble guanylate cyclase inhibitor, inhibited EFS-induced relaxation. NOR-1, a NO donor, and carbon monoxide-releasing molecule-2 (CORM-2), a CO donor, treatment relaxed the distal colon and increased cyclic GMP content. The effects of NOR-1 and CORM-2 were inhibited by ODQ. KT5823, a cyclic GMP-dependent protein kinase inhibitor, inhibited EFS-induced relaxation. EFS-induced relaxation in the presence of KT5823 was further inhibited by L-NNA, but not by SnPP-IX. In addition, KT5823 inhibited CORM-2-induced relaxation, but not NOR-1-induced relaxation. H89, a cyclic AMP-dependent protein kinase inhibitor, inhibited EFS-induced relaxation, and EFS-induced relaxation in the presence of H89 was further inhibited by L-NNA. These results suggested that NO and CO function as inhibitory neurotransmitters in the longitudinal muscle of C57BL mouse distal colon.

Non-adrenergic non-cholinergic inhibition of gastrointestinal smooth muscle and its intracellular mechanism(s)

Relaxation of gastrointestinal smooth muscle caused by release of non-adrenergic non-cholinergic (NANC) transmitters from enteric nerves occurs in several physiologic digestive reflexes. Likely candidate NANC inhibitory agents include nitric oxide (NO), adenosine triphosphate (ATP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), carbon monoxide (CO), protease-activated receptors (PARs), hydrogen sulfide (H2S), neurotensin (NT) and beta-nicotinamide adenine dinucleotide (beta-NAD). Multiple NANC transmitters work in concert, are pharmacologically coupled and are closely coordinated. Individual contribution varies regionally in the gastrointestinal tract and between species. NANC inhibition of gastrointestinal smooth muscle involves several intracellular mechanisms, including increase of cyclic guanosine monophosphate (cGMP), increase of cyclic adenosine monophosphate (cAMP) and hyperpolarization of the cell membrane via direct or indirect activation of potassium ion (K+) channels.

Involvements of PHI-nitric oxide and PACAP-BK channel in the sustained relaxation of mouse gastric fundus

The roles of nitric oxide (NO) and K(+) channels in sustained relaxation induced by electrical field stimulation (EFS) in the presence of atropine and guanethidine were studied in circular muscle strips of mouse gastric fundus. In the wild-type mouse, N(G)-nitro-l-arginine (l-nitroarginine), a nitric oxide synthase inhibitor, significantly inhibited the sustained relaxation in addition to the rapid relaxation. The sustained relaxation in pituitary adenylate cyclase-activating peptide (PACAP)-knockout mouse, which was smaller than that of the wild-type mouse, was also inhibited by l-nitroarginine. l-Nitroarginine inhibited the relaxation induced by the peptide histidine isoleucine (PHI), but not that induced by PACAP. S-Nitroso-N-acetyl-dl-penicillamine (SNAP), a NO donor, -induced relaxation was not affected by PACAP(6-38). EFS-induced sustained relaxation was inhibited by iberiotoxin, a big conductance calcium-activated K(+) (BK) channel inhibitor, but not by apamin, a small conductance calcium-activated K(+) (SK) channel inhibitor, and glibenclamide, an ATP-sensitive K(+) channel inhibitor. The relaxation that remained after the iberiotoxin-treatment was significantly inhibited by l-nitroarginine. Iberiotoxin inhibited PACAP-induced relaxation, while it had no effect on both PHI- and SNAP-induced relaxation. Immunoreactivities to anti-BK channel and anti-PHI antibodies were found in the circular muscle and the myenteric plexus layers, respectively. These results suggest interplay between PHI and NO in the sustained relaxation of the mouse gastric fundus, and that BK channels are involved in the PACAP-component of the sustained relaxation.

Inhibitory effects of alendronate on cholinergic responses in rat lower esophageal sphincter

Alendronate is a potent inhibitor of osteoclast-mediated bone resorption, but its use results in serious esophageal damage. In order to clarify the latter, we examined the effects of alendronate on electrical field stimulation-induced responses in the rat lower esophageal sphincter. Electrical field stimulation induced atropine-sensitive contraction. Alendronate inhibited electrical field stimulation-induced contraction in a concentration-dependent manner. In the presence of N(G)-nitro-L-arginine (L-nitroarginine), electrical field stimulation elicited a strong cholinergic contraction. This contraction was also inhibited by alendronate, to a similar extent as that seen in the absence of L-nitroarginine. In lower esophageal sphincter contracted by prostaglandin F(2alpha) and treated with atropine, electrical field stimulation induced L-nitroarginine-sensitive relaxation. Alendronate did not affect relaxation. These results suggest that alendronate decreases the tone of lower esophageal sphincter by inhibiting cholinergic nervous activity.