Effect of cooling on the responsiveness of canine tracheal muscle

Cooling-induced contraction of the rat gastric fundus: mediation via transient receptor potential (TRP) cation channel TRPM8 receptor and Rho-kinase activation

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 x 10(-6) and 3 x 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 x 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.

Length-dependent modulation of smooth muscle activation: effects of agonist, cytochalasin, and temperature

We tested the hypothesis that mechanical strain modulates agonist sensitivity of smooth muscle by measuring myosin phosphorylation and contractile force in bovine tracheal smooth muscle activated by various concentrations of the muscarinic receptor agonist carbachol and at various muscle lengths. Increasing carbachol concentration by 10,000-fold did not restore myosin phosphorylation levels at shorter muscle lengths to the level at optimal length (Lo). Maximum levels of myosin phosphorylation induced by carbachol at 0.6, 0.8, and 1.0 Lo were similar but became lower at <0.6 Lo. Cytochalasin D significantly attenuated carbachol-induced contraction by 54%. In addition, cytochalasin D treatment induced a parallel downward shift in the length-myosin phosphorylation relation. Lowering temperature from 37 to 23 degrees C did not significantly change the length dependencies of carbachol-induced active force and myosin phosphorylation. These results have led us to conclude that 1) agonist sensitivity and maximum level of activation (as measured by myosin phosphorylation) are targets of length-dependent modulation, 2) actin filaments involved in contraction and length-dependent modulation are distinct in sensitivity to cytochalasin D, and 3) length-dependent modulation is relatively temperature insensitive.

Mechanism of cooling-induced relaxation in the isolated guinea-pig trachea

In this study, we explored the possible mechanism of cooling-induced relaxation of the isolated guinea-pig trachea. A rapid cooling (-4 degrees C/min) from 37 +/- 0.5 degree C to 25 +/- 0.5 degree C induced a transient and small contraction followed by a sustained cooling-relaxation. This relaxation was not blocked by propranolol or tetrodotoxin. Various concentrations of four contractile agonists (histamine, carbachol, 5-HT and ryanodine) all enhanced cooling-relaxation in a concentration-dependent manner which correlated well with their increase in the developed muscular tension, suggesting an inherent counterbalance between cooling-relaxation and the bronchoconstriction. Treating with either indomethacin or nordihydroguaiaretic acid (NDGA) did not affect the contractile properties of histamine, carbachol and 5-HT except ryanodine, but reversed cooling-relaxation into sustained cooling-contraction. Indomethacin partially inhibited but NDGA abolished cooling-relaxation induced by ryanodine. Moreover, ryanodine, but not the other three contractile agonists, could antagonize indomethacin in inducing cooling-contractions by various agonists. From above findings, we can conclude that eicosanoids including prostaglandins particularly leukotrienes, which would be produced by the elevated Ca(2+)-release from the ryanodine sensitive Ca(2+)-store, play prominent roles in inducing cooling-relaxation.