Evidence for the presence of both pre‐ and postjunctional P₂‐purinoceptor subtypes in human isolated urinary bladder

Abstract

1 In order to characterize P2-purinoceptor(s) in human urinary bladder the contractile effects of ATP and its slowly-hydrolyzable analogues m,-methylene ATP (m,P-MeATP) and P,y-methylene ATP (P,yMeATP) were investigated on human detrusor strips taken from patients undergoing cystectomy for bladder carcinoma.2 Serial concentration-response curves (SCRC) for ATP, a,-MeATP and ,Iy-MeATP were constructed with an interval of 25 min between two successive doses to avoid tachyphylaxis. ATP (10 gM-10 mM) induced a phasic contraction, which was very rapid in onset. The dose-response curve to ATP appeared not to be monophasic: at the lower concentrations (10-300pM) the curve was shallow, whilst at high concentrations (1-10 mM) the curve was steeper. The magnitude of the response obtained at the highest concentration tested (10 mM) was only 21.1 ± 2.8% (mean ± s.e.mean; n = 4) of the KCI (100 mM)-induced contraction.3 a,4-MeATP (O.3 IM-1 mM) and ,y-MeATP (10 M-1 mM) elicited a phasic contraction with a time course similar to that exhibited by ATP. The magnitude of the response obtained at the highest concentration tested (1 mM) was 70.3 ± 6.3% for a,P-MeATP (n = 10) and 27.9 ± 4.5% for ,7y-MeATP (n = 8) of KCl (100 mM)-induced contraction. The rank order of potency was MP-MeATP>P,7y-MeATP>ATP. A plateau of response could not be achieved by any of these agonists. 4 The P2-purinoceptor antagonist, suramin (10-300 tM), dose-dependently antagonized only the lower part of ax,-MeATP dose-response curve. Data were analysed in terms of dose-ratio estimated at two levels of response (10% and 35% of KC1 100 mM-induced contraction). At 10% of KCl response the Schild plot slope was 0.98 and the estimated pKB was 5.85, whereas using the dose-ratio at the 35% level of the KCl response, the Schild plot was not linear suggesting an interaction of X,1-MeATP with a heterogeneous receptor population.5 The putative P2-purinoceptor antagonist, Coomassie Brilliant Blue G (CB-G) at 0.3 and 1 llM (n = 5), shifted to the left the a,P-MeATP SCRC. The response at the highest concentration of agonist was potentiated, being equal to 78.8 ± 11.7% of the KCl (100 mM) response (n = 5). CB-G at 0.3 LM also shifted to the left the ,Iy-MeATP SCRC and significantly potentiated the response at 1 mM up to 46.3 ± 5.6% of KCl 100 mM response (n = 4).6 Pretreatment with terodotoxin (TTX) at 1 lM shifted to the left the a,P-MeATP SCRC but the response to the highest concentration of the agonist was not potentiated, being 73.6 ± 9.9% of the KCl (100 mM) response (n = 5). TTX (1I M) shifted to the left the P,7-MeATP SCRC and significantly potentiated the response at 1 mM (61.6 ± 3.1% of KCl response; n = 4). 7 The NO synthase inhibitor NW-nitro-L-arginine methyl ester (L-NAME) at 100 gM did not modify the SCRC to either tp or P,y-MeATP. 8 We conclude that in human detrusor muscle there is a heterogeneity of purinoceptors. The complex antagonism exhibited by suramin suggests the presence not only of Ph-purinoceptors but also of another contractile P2-purinoceptor s...

A re-appraisal of the nature of the atropine-resistant contraction to electrical field stimulation in the human isolated detrusor muscle

“…These contractile responses were rapid in onset, and the peak response was reached within a few (≤5) seconds. The concentration-response curve did not reach a plateau at the highest concentration tested, as previously reported (Palea et al 1995). The contractile responses to ATP were antagonized by both suramin and PPADS, in a concentration-dependent and insurmountable manner, with depression of the response to 1000 µM ATP (i.e.…”

“…Recently, the contractile responses induced by ATP and a series of ATP analogues in the human bladder have been found to be mediated by P 2X - (Hoyle et al 1989;Palea et al 1995) as well as by separate P 2 -purinoceptors not identified yet (Palea et al 1995). In spite of the presence of excitatory purinoceptors on the effector cells, the presence of purinergic transmission in the human bladder is uncertain, with the cholinergic component accounting for nearly all the excitatory neuromuscular transmission (Andersson 1993;Hoyle and Burnstock 1993).…”

Purinergic signalling in the urinary tract in health and disease

“…The authors concluded that the human detrusor muscle contains two contractile purinoceptor subtypes: one is activated by α,β-meATP and is probably a P2X receptor; the other receptor is activated by ADPβS and appears to be different from those which are included in the current classification system. In a later paper from this group [542], evidence was presented for prejunctional P2 receptors on parasympathetic nerve terminals as well as two postjunctional P2 receptor subtypes, one of which was insensitive to suramin. ATP-induced contractions were reduced about 30 % by indomethacin, indicating involvement of PGs, by 48 % after nifedipine and were abolished in Ca 2+ -free medium [323].…”

P2-receptors of the urinary bladder as potential targets for novel drugs

“…Существуют очевидные фармакологиче-ские доказательства наличия P2X-рецепто-ров в мочевом пузыре человека, где АТФ, α-β-метилен-АТФ, ADP-бета-S и динукле-отидные фосфаты вызывают сокращения [37][38][39][40]. Сокращения, вызванные АТФ, уг-нетались на 30% индометацином (что ука-зывает на участие простагландинов), на 48% -нифедипином (антагонистом мед-ленных кальциевых каналов), полностью исчезали в среде, свободной от кальция [38].…”