Evidence for two distinct P₂‐purinoceptors subserving contraction of the rat anococcygeus smooth muscle

Abstract

1 The effects of the P2-purinoceptor agonists, adenosine 5'-triphosphate (ATP), a,fl-methylene ATP (a,f,-MeATP), fl,y-methylene ATP (fi,y-MeATP), L-fi,y-methylene ATP (L-fi,y-MeATP), adenosine-5'-O-(2-thiodiphosphate) (ADPfS), and 2-methylthio ATP (2-MeSATP) were investigated on the isometric tension of the rat anococcygeus muscle.2 Non-cumulative additions of ATP (100-1500MM), a,f,-MeATP (1-300yM), 13,'y-MeATP (10-300 pM), L-fy-MeATP (3-100 pM) and ADPfS (1-100 gM) produced concentration-dependent contractions, whereas 2-MeSATP (1-100pM) had no effect. The rank order of potency was a,,f- 6 The findings suggest that in the rat anococcygeus, smooth muscle cells are endowed with two distinct P2-purinoceptors which subserve contractions: a P2x-purinoceptor activated by ATP and its analogues, and another type of P2-purinoceptor activated by ADPfiS.

Effects of P2-receptor agonists on sympathetic neuroeffector transmission in the rat isolated anococcygeus muscle

“…The first application of α,β-MeATP produced a transient contraction by activating postjunctional P2X-receptors, as reported previously in this tissue (Najbar et al 1996), and thereafter, in its continued presence, the stimulation-induced contractions (1 Hz for 10 s) were enhanced. With cumulative increases in concentration, there were no further drug-induced contractions due to desensitisation of the P2X-receptors as reported previously (Najbar et al 1996). In contrast, with cumulative addition of α,β-MeATP, the stimulationinduced contractions were further enhanced.…”

“…With each concentration, the enhancement developed gradually, reaching a stable level after 15-20 min of exposure, and disappeared gradually over a 15-20 min period after washing it out. NADPH and ADPβS produced similar effects; however, the direct contraction to ADPβS did not fully return to baseline levels, as observed previously (Najbar et al 1996). Quantitative experiments on the enhancing effect were carried out with non-cumulative addition of drugs.…”

“…The tissue was then exposed to 8-(p-sulfophenyl)-theophylline (8SPT, 30 µM, 10 min), suramin (100 µM, 30 min), pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 µM, 60 min), reactive blue 2 (100 µM, 30 min), L-β,γ-methylene adenosine 5'-triphosphate (L-β,γ-MeATP, 10 µM, 20 min), N G -nitro-L-arginine methyl ester (L-NAME, 100 or 300 µM, 15-22 min), desipramine (1 µM, 30 min) or idazoxan (0.1 µM, 15 min). The concentrations and pre-exposure times for these drugs were sufficient for blockade of prejunctional P1-receptors (8SPT), postjunctional P2-receptors (suramin, PPADS, reactive blue 2 and desensitisation with L-β,γ-MeATP), nitrergic relaxations (L-NAME), neuronal uptake of noradrenaline (desipramine) and α 2 -adrenoceptors (idazoxan), in the rat anococcygeus muscle (Hobbs and Gibson 1990;Gillespie 1980;Najbar et al 1994aNajbar et al , 1996. Subsequently, the agonist used previously was introduced.…”

Coexpression of Ligand-gated P2X and G Protein-coupled P2Y Receptors in Smooth Muscle

“…The functional status of P 2Y5 which has low homology to other P 2Y receptors has not been resolved (16,25), while the P 2Y7 receptor has now been identified as the leukotriene B 4 receptor (26). P 2Y receptors are variously coupled to pertussis toxin-sensitive and -insensitive G proteins which activate or inhibit various effector enzymes including phospholipase C-␤ (PLC-␤) (15,16,(27)(28)(29)(30), phospholipase D (31, 32), phospholipase A 2 (33), and adenylyl cyclase (28,30,34).ATP, UTP, and AMP-PCP can mobilize Ca 2ϩ and elicit contractile responses in vascular and visceral smooth muscle suggesting that both P 2X and P 2Y receptors are present (15,17,(35)(36)(37). Their co-existence raises the question as to which receptor subtype mediates preferentially the action of the endogenous ligand, ATP.…”

“…ATP, UTP, and AMP-PCP can mobilize Ca 2ϩ and elicit contractile responses in vascular and visceral smooth muscle suggesting that both P 2X and P 2Y receptors are present (15,17,(35)(36)(37). Their co-existence raises the question as to which receptor subtype mediates preferentially the action of the endogenous ligand, ATP.…”