1. Cooling has been shown to induce contractions of several smooth muscles in vitro. However, the mechanism involved in the response is not yet known. In the present study, we investigated the possible involvement of transient receptor potential (TRP) cation channel TRPM8 receptors and the Rho-kinase pathway in cooling-induced contraction of the rat fundus.
2. Cooling-induced contractions were inversely proportional to temperature. Contractions were significantly reduced (by 65.6 ± 2.4%; P < 0.05) in a Ca2+-free (1 mmol/L EGTA) medium, but were not significantly inhibited by nifedipine (10−6 mol/L).
3. Capsazepine (3 × 10−6 and 3 × 10−5 mol/L), a TRPM8 receptor antagonist, inhibited cooling-induced contraction of the rat gastric fundus.
4. The Rho-kinase inhibitor Y-27632 concentration-dependently inhibited cooling-induced contraction of the gastric fundus, producing approximately 90% inhibition at a concentration of 10−5 mol/L. Contractions were also inhibited by genistein (3 × 10−5 mol/L), a tyrosine kinase inhibitor, but not by GF 109203X (10−7 mol/L), a protein kinase C inhibitor.
5. Using reverse transcription–polymerase chain reaction techniques, it was observed that the mRNA for the TRPM8 receptor and Rho-kinase were expressed in the rat gastric fundus.
6. These results would suggest that cooling-induced contraction of the rat fundus is mediated by activation of TRPM8 receptors via a mechanism involving activation of Rho-kinase.