Gastroenterology

Gastroenterology

Volume 116, Issue 3, March 1999, Pages 586-592
Gastroenterology

Alimentary Tract
Protease-activated receptors mediate apamin-sensitive relaxation of mouse and guinea pig gastrointestinal smooth muscle,☆☆

https://doi.org/10.1016/S0016-5085(99)70180-0Get rights and content

Abstract

Background & Aims: Protease-activated receptor (PAR)-1 and PAR-2 are expressed on gastrointestinal smooth muscle, but knowledge of their functionality is limited. The aim of this study was to determine if PAR-1 and PAR-2 mediate gastrointestinal smooth muscle relaxation and to clarify the underlying mechanisms. Methods: Responses to PAR activation using the serine proteases thrombin and trypsin and the peptide agonists for PAR-1 and PAR-2, SFLLRN-NH2 and SLIGRL-NH2, respectively, were investigated in submaximally contracted longitudinal strips of mouse gastric fundus and guinea pig taenia coli. Results: In mouse gastric fundus, both thrombin and trypsin caused relaxations followed by contractions. SFLLRN-NH2 and SLIGRL-NH2 caused similar biphasic responses, the relaxation components of which were eliminated by apamin or ryanodine. For SFLLRN-NH2, apamin and ryanodine revealed contractions. Nifedipine inhibited both relaxations and contractions to each peptide. In guinea-pig taenia coli, thrombin but not trypsin caused relaxation, whereas SFLLRN-NH2 and SLIGRL-NH2 caused concentration-dependent relaxations that were eliminated by apamin but were unaffected by ryanodine. Conclusions: The mouse gastric fundus and guinea pig taenia coli contain functional PAR-1 and PAR-2 that mediate relaxations via ryanodine-sensitive and -insensitive activation of small-conductance, Ca2+-activated K+ channels. We propose that smooth muscle PARs act as sensors for inflammatory signals in gut and respond by inhibiting gut motility during peritoneal infections or tissue damage.

GASTROENTEROLOGY 1999;116:586-592

Section snippets

Tissue preparation

Male Balb-c mice (20–30 g) and Hartley Tri-colored male and female guinea pigs (200–400 g) were killed by cervical dislocation with approval from the University of Melbourne Animal Experimentation Ethics Committee. The mouse stomach was isolated and cleared of its contents, and the fundic region was cut into two longitudinal strips (3 × 10 mm). Some strips had the mucosa removed by careful dissection under a microscope. Approximately 5-mm-long segments of the taenia coli were removed with

Mouse gastric fundus

Thrombin (0.3 U/mL) and trypsin (0.3 U/mL) caused biphasic responses in the mouse gastric fundus that consisted of an initial relaxation with maxima of 31.7% ± 3.7% (n = 7) and 34.7% ± 5.5% (n = 8) followed by contractions of 11.4% ± 3.4% (n = 7) and 31.7% ± 7.1% (n = 8), respectively (Figure 1).

. Digitized original traces showing responses to a single concentration (↓) of the serine proteases (A) thrombin (0.3 U/mL) and (B) trypsin (0.3 U/mL) in separate strips of mouse gastric fundus

Discussion

Although Corvera et al.13 showed that PAR-2 activation inhibited spontaneous contractile activity in the rat isolated distal colon, our study is the first to show that both PAR-1 and PAR-2 mediate direct relaxation of gastrointestinal smooth muscle and that these relaxations are able to largely mask previously reported contractile effects of both enzymes (thrombin and trypsin) and peptide activators of PARs in the gut.7, 17, 18 Our study also shows that relaxations to the PAR-1 and PAR-2

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    Address requests for reprints to: Thomas M. Cocks, Ph.D., Department of Pharmacology, Tri-radiate Building, Parkville, Victoria 3052, Australia. e-mail: [email protected]; fax: (61) 3-934-71452.

    ☆☆

    Supported by the National Health and Medical Research Council of Australia.

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