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MUCOSAL BIOLOGY

P2Y₁ receptors mediate inhibitory purinergic neuromuscular transmission in the human colon

¹Department of Cell Biology, Physiology, and Immunology, Universitat Autònoma de Barcelona, Bellaterra; and ²Department of Surgery, Hospital de Mataró, Spain; and ³Fundació de Gastroenterologia Dr. F. Vilardell, Barcelona, Spain

Submitted 17 November 2005 ; accepted in final form 25 April 2006

Indirect evidence suggests that ATP is a neurotransmitter involved in inhibitory pathways in the neuromuscular junction in the gastrointestinal tract. The aim of this study was to characterize purinergic inhibitory neuromuscular transmission in the human colon. Tissue was obtained from colon resections for neoplasm. Muscle bath, microelectrode experiments, and immunohistochemical techniques were performed. 2'-deoxy-N⁶-methyl adenosine 3',5'-diphosphate tetraammonium salt (MRS 2179) was used as a selective inhibitor of P2Y₁ receptors. We found that 1) ATP (1 mM) and adenosine 5'--2-thiodiphosphate (ADPS) (10 µM), a preferential P2Y agonist, inhibited spontaneous motility and caused smooth muscle hyperpolarization (about –12 mV); 2) MRS 2179 (10 µM) and apamin (1 µM) significantly reduced these effects; 3) both the fast component of the inhibitory junction potential (IJP) and the nonnitrergic relaxation induced by electrical field stimulation were dose dependently inhibited (IC₅₀ 1 µM) by MRS 2179; 4) ADPS reduced the IJP probably by a desensitization mechanism; 5) apamin (1 µM) reduced the fast component of the IJP (by 30–40%) and the inhibitory effect induced by electrical field stimulation; and 6) P2Y₁ receptors were localized in smooth muscle cells as well as in enteric neurons. These results show that ATP or a related purine is released by enteric inhibitory motoneurons, causing a fast hyperpolarization and smooth muscle relaxation. The high sensitivity of MRS 2179 has revealed, for the first time in the human gastrointestinal tract, that a P2Y₁ receptor present in smooth muscle probably mediates this mechanism through a pathway that partially involves apamin-sensitive calcium-activated potassium channels. P2Y₁ receptors can be an important pharmacological target to modulate smooth muscle excitability.

smooth muscle relaxation; purinergic receptors; inhibitory junction potential

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