Premium
Mechanisms Of α,β‐Methylene ATP‐Induced Inhibition In Rat Ileal Smooth Muscle: Involvement Of Intracellular Ca 2+ Stores In Purinergic Inhibition
Author(s) -
Storr M,
Franck H,
Saur D,
Schusdziarra V,
Allescher HD
Publication year - 2000
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1046/j.1440-1681.2000.03334.x
Subject(s) - apamin , purinergic receptor , ppads , carbachol , endocrinology , medicine , chemistry , charybdotoxin , channel blocker , adenosine , p2y receptor , pertussis toxin , biology , receptor , g protein , potassium channel , biochemistry , calcium
SUMMARY 1. In order to investigate purinergic effects on rat ileal smooth muscle, we used α,β‐methylene ATP (α,β‐MeATP), ATP, ADP and UTP. α,β‐Methylene ATP and ATP were the only agonists that caused a concentration‐dependent inhibition of carbachol‐precontracted smooth muscle. The inhibitory effect of α,β‐MeATP was completely blocked by pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (3 × 10 –5 mol/L), a selective antagonist of the P2X > > P2Y receptor. 2. Using reverse transcription–polymerase chain reaction we demonstrated the presence of both, P2X and P2Y receptor mRNA within the rat ileal longitudinal muscle/myenteric plexus layer preparation. 3. The α,β‐MeATP‐induced inhibition was blocked in a concentration‐dependent manner in the presence of the K + channel blocker apamin, but was unaffected by other K + channel blockers, such as charybdotoxin (10 –7 mol/L), 4‐aminopyridine (10 –4 mol/L), glibenclamide (10 –5 mol/L) and tetraethylammonium (10 –3 mol/L). 4. The α,β‐MeATP‐induced inhibition was unaffected by pretreatment with atropine (10 –6 mol/L), phentolamine (10 –6 mol/L), propranolol (10 –6 mol/L), nitrendipine (10 –7 mol/L), pertussis toxin (10 –6 mol/L) N G ‐nitro‐ L ‐arginine (3 × 10 –4 mol/L) and tetrodotoxin (10 –6 mol/L), excluding an involvement of adrenergic, cholinergic, neural, nitrinergic or G‐protein involvement in purinergic‐mediated inhibition. 5. In order to investigate whether the internal Ca 2+ stores participated in the inhibitory effect observed, we depleted internal Ca 2+ stores with cyclopiazonic acid, a specific Ca 2+ ‐ATPase inhibitor. The inhibitory effect of α,β‐MeATP was completely abolished after depletion of the intracellular Ca 2+ stores. 6. This is in contrast with the effects seen for neurotensin, where neurotensin‐induced inhibition was unchanged after depletion of intracellular Ca 2+ stores, suggesting at least two different pathways of apamin‐sensitive non‐adrenergic, non‐cholinergic inhibition in rat ileal smooth muscle. 7. According to our results, the inhibitory effect of α,β‐MeATP in rat ileum longitudinal smooth muscle is mediated via a P 2 purinoceptor, most likely a P2X receptor, involves G‐protein‐independent activation of an apamin‐sensitive K + channel and requires filled intracellular Ca 2+ stores.