Evidence that ATP or a related purine is an excitatory neurotransmitter in the longitudinal muscle of mouse distal colon.
OBJECTIVE
This study analysed the contribution of the purinergic system to enteric neurotransmission in the longitudinal muscle of mouse distal colon.


METHODS
Motor responses to exogenous ATP and to nerve stimulation in vitro were assessed as changes in isometric tension.


RESULTS
ATP induced a concentration-dependent contraction, reduced by 4-[[4-formyl-5-hydroxy-6-methyl-3-[(phosphonooxy)methyl]-2-pyridinyl]azo]-1,3-benzene disulphonic acid (PPADS), suramin, P2Y purinoreceptor desensitisation with adenosine 5'-O-2-thiodiphosphate (ADPbetaS), and atropine, but unaffected by P2X purinoceptor desensitisation with alpha,beta-methylene ATP (alpha,beta-meATP) and by 2,2-dimethyl-propionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethyl-propionyloxymethyl)-propyl ester (MRS 2395), a P2Y(12) selective antagonist. The response to ATP was increased by 2'-deoxy-N(6)-methyl adenosine 3',5'-diphosphate (MRS 2179), a P2Y(1) selective antagonist, tetrodotoxin (TTX) or N(omega)-nitro-L-arginine methyl ester (L-NAME). ADPbetaS, a P2Y-purinergic agonist, induced muscular contraction, with the same pharmacological profile as the ATP-induced contraction. ADP, a natural ligand for P2Y(1) receptors, induced muscular relaxation, antagonized by MRS 2179 and by TTX or L-NAME. Nerve stimulation elicited a transient nitrergic relaxation, followed by contraction. Contractile responses was reduced by atropine, PPADS, suramin, P2Y purinoceptor desensitisation, but not by P2X purinoceptor desensitisation, MRS 2179 or MRS 2395. None of the purinergic antagonists modified the nerve-evoked relaxation.


CONCLUSIONS
In the longitudinal muscle of mouse distal colon, ATP, through ADPbetaS-sensitive P2Y purinoceptors, contributed to the excitatory neurotransmission acting directly on smooth muscle and indirectly via activation of cholinergic neurons. Moreover, P2Y1 purinoceptors appear to be located on nitrergic inhibitory neurons. This study provides new insights into the role of purines in the mechanism inducing intestinal transit in mouse colon.
Zizzo
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1Dipartimento di Biologia Cellulare e dello Sviluppo, Laboratorio di Fisiologia generale, Università di Palermo, Viale delle Scienze, Palermo, Italia.
Mulè
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F
Serio
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D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D003106:Colon / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D058913:Purinergic Agonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014631:Valerates / Q000494:pharmacology
C528918:2,2-dimethylpropionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethylpropionyloxymethyl)propyl ester; D018377:Neurotransmitter Agents; D058913:Purinergic Agonists; D013873:Thionucleotides; D014631:Valerates; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; C030812:adenosine 5'-O-(2-thiodiphosphate); D011732:Pyridoxal Phosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000225:Adenine