Summarized data showing the average change in smooth muscle membrane potential to β-adrenoceptor agonists and to agonists with various antagonists present. (A) Hyperpolarization to increasing concentrations of isoprenaline (n = 23), dobutamine and salbutamol (n = 13 and 7 respectively). (B) Hyperpolarization to increasing concentrations of isoprenaline in the presence of 1 µM atenolol (n = 3, P < 0.001), 100 nM ICI 118,551 (n = 4, N.S.) or 100 nM propranolol (n = 4, P < 0.001) (C) to noradrenaline in the presence of either 1 µM atenolol (n = 3, P < 0.001), 100 nM ICI 118,551 (n = 6, N.S.) or 100 nM propranolol (n = 6, P < 0.001) (D) to adrenaline in the presence of either 1 µM atenolol (n = 4, N.S.), 100 nM ICI 118,551 (n = 4, N.S.) or 100 nM propranolol (n = 4, P < 0.001). N.S., not significant.