TRPM8 Channel Activation Reduces the Spontaneous Contractions in Human Distal Colon

Abstract

The transient receptor potential-melastatin 8 (TRPM8) is a non-selective Ca2+-permeable channel, activated by cold, membrane depolarization, and different cooling compounds. TRPM8 expression has been found in gut mucosal, submucosal, and muscular nerve endings. Although TRPM8 plays a role in pathological conditions, being involved in visceral pain and inflammation, the physiological functions in the digestive system remain unclear as yet. The aims of the present study were: (i) to verify the TRPM8 expression in human distal colon; (ii) to examine the effects of TRPM8 activation on colonic contractility; (iii) to characterize the mechanism of action. Reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting were used to analyze TRPM8 expression. The responses of human colon circular strips to different TRPM8 agonists [1-[Dialkyl-phosphinoyl]-alkane (DAPA) 2–5, 1-[Diisopropyl-phosphinoyl]-alkane (DIPA) 1–7, DIPA 1–8, DIPA 1–9, DIPA 1–10, and DIPA 1–12) were recorded using a vertical organ bath. The biomolecular analysis revealed gene and protein expression of TRPM8 in both mucosal and smooth muscle layers. All the agonists tested, except-DIPA 1–12, produced a concentration-dependent decrease in spontaneous contraction amplitude. The effect was significantly antagonized by 5-benzyloxytryptamine, a TRPM8 antagonist. The DIPA 1–8 agonist resulted in the most efficacious and potent activation among the tested molecules. The DIPA 1–8 effects were not affected by tetrodotoxin, a neural blocker, but they were significantly reduced by tetraethylammonium chloride, a non-selective blocker of K+ channels. Moreover, iberiotoxin, a blocker of the large-conductance Ca2+-dependent K+-channels, but not apamin, a blocker of small-conductance Ca2+-dependent K+ channels, significantly reduced the inhibitory DIPA 1–8 actions. The results of the present study demonstrated that TRPM8 receptors are also expressed in human distal colon in healthy conditions and that ligand-dependent TRPM8 activation is able to reduce the colonic spontaneous motility, probably by the opening of the large-conductance Ca2+-dependent K+-channels.

Spasmolytic Effects of Aphanizomenon Flos Aquae (AFA) Extract on the Human Colon Contractility

“…As previously reported [27], following the overnight storage, strips of 0.4 × 1 cm were cut parallel to the circular muscle and suspended in a four-channel organ bath in which each chamber was filled with 8 mL of Krebs solution with the following composition (mM): NaCl 119; KCl 4.5; MgSO 4 2.5; NaHCO 3 25; KH 2 PO 4 1.2; CaCl 2 2.5; glucose 11.1 and aerated with 5% CO 2 , 95% O 2 , pH 7.4 at 37 • C.…”

TRPV3 and TRPV4 as candidate proteins for intestinal ammonium absorption

“…Notably, mRNA for TRPM8 was also not found in the rumen 14 or in the human intestine 65 . However, expression by human colonic muscle has been reported with weaker expression within the mucosa 66 …”

Advances in TRP channel drug discovery: from target validation to clinical studies

“…Wet dog shakes rapid and alternating head rotation in rats, an animal model used to quantify central 5-HT2A activity. reduce spontaneous painful contractions in the human distal colon 102 .…”

“…Although most of the attention was focused on antagonists, TRPM8 agonists (such as WS-12 and di-isopropyl-phosphinoyl-alkane, DIPA) also have an analgesic potential. For instance, DIPA was shown to reduce spontaneous painful contractions in the human distal colon 102 .…”