ATP release and contraction mediated by different P2-receptor subtypes in guinea-pig ileal smooth muscle.
1. The present study was addressed to clarify the subtypes of P2-purinoceptor involved in ATP release and contraction evoked by alpha, beta-methylene ATP (alpha, beta-mATP) and other P2-agonists in guinea-pig ileum. 2. alpha, beta-mATP 100 microM produced a transient and steep contraction followed by ATP release from tissue segments. These maximum responses appeared with different time-courses and their ED50 values were 5 and 25 microM, respectively. The maximum release of ATP by alpha, beta-mATP was markedly reduced by 250 microM suramin, 30 microM pyridoxal-phosphate-6-azophenyl-2',5'-disulphonic acid (PPADS) and 30 microM reactive blue 2 (RB-2), P2-receptor antagonists. However, the contractile response was inhibited by suramin, tetrodotoxin and atropine, but not by PPADS and RB-2. 3. Although the contraction caused by alpha, beta-mATP was strongly diminished by Ca(2+)-removal and nifedipine, and also by tetrodotoxin and atropine at 0.3 microM, the release of ATP was virtually unaffected by these procedures. 4. UTP, beta, gamma-methylene ATP (beta, gamma-mATP) and ADP at 100 microM elicited a moderate release of ATP. The release caused by UTP was virtually unaffected by RB-2. However, these P2-agonists failed to elicit a contraction of the segment. 5. The potency order of all the agonists tested for the release of ATP was alpha, beta-mATP > UTP > beta, gamma-mATP > ADP. 6. In superfusion experiments with cultured smooth muscle cells from the ileum, alpha, beta-mATP (100 microM) enhanced the release of ATP 5 fold above the basal value. This evoked release was inhibited by RB-2. 7. These findings suggest that ATP release and contraction induced by P2-agonists such as alpha, beta-mATP in the guinea-pig ileum result mainly from stimulation of different P2-purinoceptors. P2Y-like purinoceptors on the smooth muscles and, probably, P2X-purinoceptors on cholinergic nerve terminals, respectively. However, the ATP release may also be mediated, in part, by P2U-receptors, because UTP caused RB-2-insensitive ATP release.
Matsuo
K
K
Department of Pharmacology, School of Medicine, Fukuoka University, Japan.
Katsuragi
T
T
Fujiki
S
S
Sato
C
C
Furukawa
T
T
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D006168:Guinea Pigs; D007082:Ileum / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000502:physiology; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000145:classification / Q000502:physiology*
D018048:Receptors, Purinergic P2; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate