Investigation of the actions of PPADS, a novel P2x-purinoceptor antagonist, in the guinea-pig isolated vas deferens.
1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) was investigated for its ability to act as an antagonist at P2x-purinoceptors which mediate neurogenic excitatory junction potentials (e.j.ps) and contractions in the guinea-pig isolated vas deferens. 2. PPADS (10(-7) M) caused a small potentiation of the phasic, predominantly purinergic component of contractions evoked by symapthetic nerve stimulation, but higher concentrations of PPADS (3 x 10(-6)-3 x 10(-5) M) elicited a substantial and significant concentration-dependent inhibition. In contrast, over the same concentration-range, PPADS had no effect on the tonic, predominantly noradrenergic phase. 3 PPADS (3 x 10(-5) M) also inhibited contractile responses to exogenous alpha,beta-methyleneATP (10(-8)-10(-3)M), a P2x-purinoceptor agonist, without affecting the responses to exogenous noradrenaline (10(-8)-10(-3) M), carbachol (10(-5) M) or histamine (10(-4) M). 4. PPADS (10(-7)-3 x 10(-5) M) produced a concentration-dependent reduction in e.j.p. magnitude and resting membrane potential. The maximum effect was seen at 10(-5) M PPADS, which reduced e.j.p. magnitude from 13.7 +/- 0.6 mV (n = 12) to 1.8 +/- 0.7 mV (n = 12) and membrane potential from -64.8 +/- 0.6 mV (n = 51) to -55.0 +/- 1.8 mV (n = 12). 5. The PPADS-induced depolarization was not inhibited by the P2x-purinoceptor antagonist, suramin (10(-4) M). This indicates that the depolarization was not due to an agonist action of PPADS at P2x-purinoceptors. 6. The results support the proposal that PPADS is a selective antagonist at P2x purinoceptors as opposed to non-P2-purinoceptors in the guinea-pig vas deferens, but its ability to cause membrane depolarization independently of P2x-purinoceptors and also, at a low concentration, to potentiate the phasic component of the neurogenic contraction indicates that it has other actions.
McLaren
G J
GJ
Department of Physiology and Pharmacology, Royal College, University of Strathclyde, Glasgow.
Lambrecht
G
G
Mutschler
E
E
Bäumert
H G
HG
Sneddon
P
P
Kennedy
C
C
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000648:ultrastructure; D009638:Norepinephrine / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D014649:Vas Deferens / Q000187:drug effects* / Q000294:innervation / Q000648:ultrastructure
D058919:Purinergic P2 Receptor Antagonists; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D006632:Histamine; D000255:Adenosine Triphosphate; D002217:Carbachol; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D009638:Norepinephrine