The differential contractile responses to capsaicin and anandamide in muscle strips isolated from the rat urinary bladder

Abstract

The contractile responses to capsaicin and anandamide, exogenous and endogenous agonists for transient receptor potential vanilloid receptor 1 (TRPV1), respectively, were investigated in muscle strips isolated from the rat urinary bladder. Capsaicin and anandamide produced concentration-dependent contractions of the muscle strips. The contractile response induced by capsaicin disappeared within approximately 20 min. In contrast, anandamide produced contractile responses lasting at least for 30 min. Capsaicin produced additive contractile responses in anandamide-treated muscle strips. The contractile response to anandamide was attenuated, but not abolished in strips desensitized by capsaicin. The response to capsaicin was abolished in the presence of a TRPV1 antagonist, N-(4-tertiarybutylphenyl)-4-(3-chlorphyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC), but not altered in the presence of either tetrodotoxin, atropine or indomethacin. In the presence of SR140333, a tachykinin NK(1) receptor antagonist or SR48968, an NK(2) receptor antagonist, the response to capsaicin was attenuated. The response to anandamide was partially attenuated in the presence of ONO8130, a prostanoid EP(1) receptor antagonist, URB597, a fatty-acid amide hydrolase inhibitor, BCTC, SR140333 or SR48968, and almost completely abolished by indomethacin. Neither tetrodotoxin, atropine, a cannabinoid CB(1) receptor antagonist, AM251, nor a cannabinoid CB(2) receptor antagonist, AM630, had any effect on the response to anandamide. These results indicate that capsaicin produces muscle contractions by stimulating the TRPV1 receptor, followed by release of neuropeptides that can activate tachykinin NK(1) and/or NK(2) receptors in the bladder and that the contractile response to anandamide is mediated at least in part by activation of prostanoid EP(1) receptors due to production of prostaglandins in addition to TRPV1 receptor activation.

Fig. 1

Representative tracings showing the contractitle responses to capsaicin and anandamide in muscle strips isolated from the rat urinary bladder.

Fig. 2

The comparison of the contractiles response to capsaicin and anandamide in muscle strips isolated from the rat urinary bladder A) Concentration response curves of capsaicin and anandamide. B) Time couses of disappearance of contractile responses to capsaicin and anandamide. Results are expressed as a percentage of the maximal response induced by 10⁻⁶M carbachol (CCh). Each point represents the mean ± S.E.M. of six to seven experiments.

Fig. 3

Representative tracings showing the cross reaction between capsaicin and anandamide in muscle strips isolated from the rat urinary bladder.

Fig. 4

The contractile response to anandamide in capsaicin-desensitized strips. Results are expressed as a percentage of the maximal response induced by 10–6M carbachol (CCh). Each bar represents the mean ± S.E.M. of six to seven experiments. * P<0.05: significant difference to the intact group (Student’s t-test).

Fig. 5

The effects of various drugs on contractile responses to capsaicin in muscle strips isolated from the rat urinary bladder. A) Tetrodotoxin, atropine, indomethacin and BCTC. B) SR140333, a tachykinin NK₁ receptor antagonist. C) SR48968, a tachykinin NK₂ receptor antagonist. Results are expressed as a percentage of the maximal response induced by 10⁻⁶M carbachol (CCh). Each bar represents the mean ± S.E.M. of four to seven experiments. * P<0.05, ** P<0.01: significant difference to the intact group (Dunnett’s multiple comparison test).

Fig. 6

The effects of various drugs on contractile responses to anandamide in muscle strips isolated from the rat urinary bladder. A) Tetrodotoxin and atropine. B) AM251, a cannabinoid CB₁ receptor antagonist and AM630, a cannabinoid CB₂ receptor antagonist. C) Capsaicin-desensitization and BCTC. D) SR140333 and SR48968. E) Indomethacin, URB597, a FAAH inhibitor and ONO8130, a prostanoid EP₁ receptor antagonist. Results are expressed as a percentage of the maximal response induced by 10⁻⁶M carbachol (CCh). Each bar reprsents the mean ± S.E.M. of four to seven experiments. * P<0.05, ** P<0.01: significant difference to the intact group (Dunnett’s multiple comparison test).