Enhancement of sympathetic purinergic neurotransmission in the guinea‐pig isolated vas deferens by the novel ecto‐ATPase inhibitor ARL 67156

Abstract

1 Field stimulation of the sympathetic nerves of the guinea-pig isolated vas deferens with trains of pulses for 20 s at 1-8 Hz produced characteristic biphasic contractions. The effect of the novel ectoATPase inhibitor, 6-N,N-diethyl-D-13,y-dibromomethyleneATP (ARL 67156, formerly known as FPL 67156), on the magnitude of the initial, predominantly purinergic peak of this response was studied in order to determine the influence of enzymatic degradation of adenosine 5'-triphosphate (ATP) on its action as a neurotransmitter. 2 The peak magnitude of the response to nerve stimulation was significantly increased in a concentration-dependent manner by ARL 67156 (5-100 rM) and the size of the neurogenic response at 4 Hz was approximately doubled in the presence of ARL 67156 (100 gM). 3 ARL 67156 (100 gM) has a rapid onset of action. The enhancing effect on neurogenic contractions was maximal after 10 min, was well maintained for at least 30 min and was rapidly reversed, with responses returning to control levels 10 min after washout.4 The neurogenic contraction in the presence of prazosin (0.1 gM) was purely purinergic, as it was abolished by the P2-purinoceptor antagonist, PPADS (100 /M). ARL 67156 (100 /M) produced a similar degree of enhancement of neurogenic responses in the absence and presence of prazosin, supporting the view that the enhancing effects of ARL 67156 on neurogenic contractions result from potentiation of the action of ATP.5 Exogenous ATP and a,,B-methyleneATP produced rapid transient contractions. Responses to ATP were increased in magnitude and duration in the presence of ARL 67156 (100 gM), whereas those to the stable analogue, cx,fl-methyleneATP were not significantly affected.6 Contractions to exogenous noradrenaline (10 gM) and KCl (40 mM) were significantly enhanced by ARL 67156 (100 gM), but this potentiation was abolished by PPADS (100 pM). Therefore, this effect of the ecto-ATPase inhibitor may be due to a build up of endogenous ATP, increasing the sensitivity of the smooth muscle to other agonists. 7 It is concluded that ARL 67156 potentiates the action of ATP, and that when ATP acts as a neurotransmitter its postjunctional actions are greatly attenuated by enzymatic degradation.

The physiological function of lower urinary tract smooth muscle

“…In bladders exhibiting DO either excess ATP is released, or ATP is less effectively broken down in the junction. Evidence for the latter possibility was obtained when it was shown that ectoATPase activity is reduced in detrusor samples from human DO bladders (Harvey et al, 2002), corroborated by other observations that show enhancement of the nerve-mediated contraction in the presence of ectoATPase inhibitors such as ARL 67156 (Westfall et al, 1996(Westfall et al, , 1997. This observation provides one target for reducing contractions in the overactive bladder, but has yet to be clinically exploited.…”

Ecto-Nucleotidases and Nucleoside Transporters Mediate Activation of Adenosine Receptors on Hippocampal Mossy Fibers by P2X7Receptor Agonist 2′-3′-O-(4-Benzoylbenzoyl)-ATP

“…The first reaction of hydrolysis of ATP is catalyzed by ecto-NTPDases (E-NTPDases), a family of enzymes reviewed by Zimmermann (2000). E-NTPDases catabolize ATP to ADP and ATP/ADP to AMP, and they can be inhibited by ARL 67156 (Crack et al, 1995;Westfall et al, 1996Westfall et al, , 2000Mihaylova-Todorova et al, 2002). Consistent with the idea that BzATP is similarly metabolized as ATP before it can activate GIRK channels, ARL 67156 abolished BzATP-induced currents (Fig.…”

Effects of cooling and ARL 67156 on synaptic ecto-ATPase activity in guinea pig and mouse vas deferens

“…The effects of cooling and of the specific ecto-ATPase inhibitor, ARL 67156, on EJPs have been suggested to be consistent with a role of the ecto-ATPase in modulating purinergic neurotransmission in the rodent vas deferens (Cunnane and Manchanda, 1988;Westfall et al, 1996). However, there have been no reports of direct estimations of the activity of this enzyme in the above conditions, i.e., change of temperature and exposure to ARL 67156, in the rodent vas deferens.…”