Gastroenterology

Gastroenterology

Volume 125, Issue 5, November 2003, Pages 1398-1409
Gastroenterology

Basic-alimentary tract
Purinergic mechanisms contribute to mechanosensory transduction in the rat colorectum☆

https://doi.org/10.1016/j.gastro.2003.07.008Get rights and content

Abstract

Background & Aims:

Adenosine 5′-triphosphate plays a role in peripheral sensory mechanisms and, in particular, mechanosensory transduction in the urinary system. P2X3 receptors are selectively expressed on small-diameter sensory neurons in the dorsal root ganglia; sensory neurons from dorsal root ganglia L1 and S1 supply the colorectum. This study investigated whether purinergic signaling contributes to mechanosensory transduction in the rat colorectum.

Methods:

A novel in vitro rat colorectal preparation was used to elucidate whether adenosine 5′-triphosphate is released from the mucosa in response to distention and to evaluate whether it contributes to sensory nerve discharge during distention.

Results:

P2X3 receptor immunostaining was present on subpopulations of neurons in L1 and S1 dorsal root ganglia, which supply the rat colorectum. Distention of the colorectum led to pressure-dependent increases in adenosine 5′-triphosphate release from colorectal epithelial cells and also evoked pelvic nerve excitation, which was mimicked by application of adenosine 5′-triphosphate and α,β-methylene adenosine 5′-triphosphate. The sensory nerve discharges evoked by distention were potentiated by α,β-methylene adenosine 5′-triphosphate and ARL-67156, an adenosine triphosphatase inhibitor, and were attenuated by the selective P2X1, P2X3, and P2X2/3 antagonist 2′,3′-O-trinitrophenyl-adenosine 5′-triphosphate and by the nonselective P2 antagonists pyridoxyl 5-phosphate 6-azophenyl-2′,4′-disulfonic acid and suramin. Adenosine, after ectoenzymatic breakdown of adenosine 5′-triphosphate, seems to be involved in the longer-lasting distention-evoked sensory discharge. Single-fiber analysis showed that high-threshold fibers were particularly affected by α,β-methylene adenosine 5′-triphosphate, suggesting a correlation between purinergic activation and nociceptive stimuli.

Conclusions:

Adenosine 5′-triphosphate contributes to mechanosensory transduction in the rat colorectum, and this is probably associated with pain.

Section snippets

Animals

Experiments were performed with adult male and female Sprague-Dawley rats (240–320 g) that were allowed free access to food and water. Animals were killed by exposure to increasing levels of carbon dioxide and cervical dislocation in accordance with UK Home Office regulations covering Schedule One procedures.

Immunohistochemistry

After death, the animals were perfused through the aorta with 60 mL of fixative (4% formaldehyde with 0.2% picric acid). The distal colon was removed and cut transversely into 10-mm lengths

Immunohistochemistry

Many of the neurons in the L1 and S1 DRG in the rat show immunoreactivity for P2X3 (Figure 1A and B). P2X2 immunoreactivity was also shown in a subpopulation of these DRG neurons, and colocalization of P2X2 and P2X3 occurred in approximately 20% of neurons. Immunostaining for the P2X3 receptor subunit was also found in a subpopulation of cell bodies, as well as their projections in the myenteric plexus (Figure 2A) and the submucous plexus (Figures 1C and 2B) of the rat colorectum. Similarly,

Discussion

A hypothesis of purinergic mechanosensory transduction in visceral organs has been proposed.18, 19 This hypothesis states that endogenous ATP is released from epithelial cells in response to stretch and acts on P2X3 or P2X2/3 receptors to excite extrinsic afferent nerve fibers. This mechanism has already been shown to occur in the bladder8, 16, 22, 23 and ureter21; P2X antagonists reduced distention-induced sensory nerve discharge in both organs by approximately 40%, indicating that other

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    ☆

    Supported by the Hamamelis Trust, Special Trustees of the Royal Free Hospital, and Royal College of Surgeons of England.

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    Copyright © 2003 American Gastroenterological Association. Published by Elsevier Inc. All rights reserved.