Effect of Na+ pump suppression on reactivity of rat trachealis to cooling.

1. This study tests the hypothesis that suppression of Na+ pump would increase the rate of tension development and the magnitude of contraction induced by cooling in airway smooth muscle. 2. Rat tracheal preparations were incubated in ouabain for 8 h and tested hourly for their response. In a representative specimen the rate of tension development increased from the control value of 0.7 mg/s to 5.5 mg/s after 7 h of incubation in ouabain concentration of 4 X 10(-4) mol/L; likewise, the magnitude of contraction increased from the control value of 80 mg to 550 mg. 3. Using ouabain concentrations between 9 X 10(-5) mol/L and 6 X 10(-3) mol/L, the rate of tension development and the magnitude of contraction first increased in a dose-dependent manner up to 8 X 10(-4) mol/L, then declined with higher doses but the responses were still greater than the control values at all concentrations. 4. After 3 h incubation in ouabain at 8 X 10(-4) mol/L, the mean rate of tension development and the mean magnitude of contraction increased to 647% and 578% of the control value, respectively. 5. These results indicate that depression of Na+ pump results in hypersensitivity and hyper-reactivity of the airway smooth muscle to cooling.