Contraction is independent of nerve released noradrenaline or ATP. A. Original record showing contraction of rat intrapulmonary artery to 10 μM linopirdine before and then during exposure to 10 μM phentolamine. B. Original record showing contraction of rat intrapulmonary artery to 10 μM linopirdine after exposing the tissue to 10 μM phentolamine plus 1 μM α,β-methylene ATP for 30 min and then again following washout of phentolamine and α,β-methylene ATP. Calibration bars are 1 mN (vertical) and 10 min (horizontal). Drug applications are indicated. B. Histogram showing the mean amplitudes of contractile responses to 10 μM linopirdine and 1 μM XE991 under control conditions (C) and following 30 min exposure to 10 μM phentolamine (Phen) or Phen plus 1 μM α,β-methylene ATP (α,β-mATP). Responses were measured in each vessel as a percentage of the contractile response to 50 mM KCl. The number of observations is shown next to each bar.