Mechanism of action of cholera toxin on the opossum internal anal sphincter smooth muscle

Abstract

Cholera toxin (CTX), an activator of Gs protein, is an important pharmacological tool in G protein research. The effect and the mechanism of action of CTX in the gastrointestinal smooth muscle, including the internal anal sphincter (IAS), are not known. The present investigation was carried out to examine the effects of CTX on the signal transduction associated with the adenylate cyclase (AC) pathway on the basal tone of the IAS smooth muscle. CTX caused a prompt and dose-dependent fall in the basal tone of the IAS that was not affected by the neurotoxins TTX and ω-conotoxin or the nitric oxide synthase inhibitor N G-nitro-l-arginine. The cyclooxygenase inhibitor indomethacin, cAMP-dependent protein kinase inhibitor Rp-8-bromoadenosine 3′,5′ cyclic monophosphorothioate inhibited CTX-induced IAS smooth muscle relaxation. Furthermore, CTX caused a concentration-dependent relaxation of the isolated smooth muscle cells (SMC) of the IAS, which was blocked by Gsα antibody (Gsα-Ab). The IAS smooth muscle relaxation was accompanied with an increase in the GTPase activity that was also specifically blocked by Gsα-Ab. We conclude that a major part of the inhibitory action of CTX in the IAS is via the direct response of the SMC that is linked with Gs protein to the AC pathway. A part of the inhibitory action of CTX on the smooth muscle occurs via the activation of cyclooxygenase pathway. The relative contribution of such actions of CTX in the smooth muscle in the gastrointestinal motility disturbances following cholera infection remains to be determined.

Role ofpp60c-srcandp44/42MAPK in ANG II-induced contraction of rat tonic gastrointestinal smooth muscles

“…Smooth muscle strips were prepared as described previously (17). Adult Sprague Dawley rats (of either sex, ϳ250 g) were anesthetized with pentobarbital sodium (50 mg/kg ip).…”

“…Permeabilization of LES and IAS SMC. Permeabilization of LES and IAS SMC was accomplished by the method previously used in our laboratory (17). SMC from rat LES and IAS were permeabilized by incubating them in cytosolic solution (in mM): 20 NaCl, 100 KCl, 5 MgSO 4, 0.96 NaH2PO4, 25 NaHCO3, 1 EGTA, 0.48 CaCl2, and 1% BSA with saponin (75 g/ml) for 3 min at room temperature.…”

Relaxation effects of adrenomedullin in carbachol-precontracted rabbit internal anal sphincter

“…It was found that vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, NO, nifedipine, rutaecarpine, and cholera and botulinus toxins had relaxant effects on the IAS, exerted in different ways. [18][19][20][21][22] In conclusion, ADM caused in vitro relaxation of isolated precontracted rabbit IAS smooth muscle strips in a concentration-dependent way. The response of the IAS was not affected by the NO synthetase inhibitor l-NAME, the cyclooxygenase inhibitor, indomethacin, or by K ϩ channel blockers.…”

“…17 A number of drugs and chemicals have been studied to determine whether they decrease the basal and precontracted tonus of the IAS in vitro. [18][19][20][21][22] It has been shown that some drugs, such as glyceryl trinitrate (as an NO donor) could be used in the treatment of chronic anal fissure. 23 ADM has been shown to have a relaxant Background.…”

Lack of nitrate tolerance in isosorbid dinitrate- and sodium nitroprusside-induced relaxation of rabbit internal anal sphincter

“…The IAS pressure has been found to display an overshoot phenomenon in the patients with chronic anal fissure [7,8] . A number of drugs and chemicals were studied to decrease basal and precontracted tonus of IAS in vitro [9][10][11][12][13][14] . It has been showed that some drugs such as glyceryl trinitrate (GTN) and isosorbide dinitrate (ISDN) as nitric oxide (NO) donor might be used in treatment of chronic anal fissure [15,16] .…”