Bradykinin increases Na+-K+ pump activity in cultured guinea-pig tracheal smooth muscle cells

1 The effect of bradykinin on the Na+-K+ pump of airway smooth muscle was investigated by measuring ouabain-sensitive Rb-86(+) uptake in cultured guinea-pig tracheal smooth muscle cells. 2 Bradykinin induced a concentration-dependent increase in ouabain-sensitive Rb-86(+) uptake, with an EC50 of 3 nM (pD(2)=8.50 +/-0.10). Stimulation was not affected by indomethacin (1 mum) suggesting that it is not mediated by cycloxygenase products of arachidonic acid. 3 The B-1 receptor agonists Lys-des-Arg(9)-bradykinin and des-Arg(9)-bradykinin had no effect on ouabain-sensitive Rb-86(+) uptake. In contrast, the B-1 and B-2 receptor agonist Lys-bradykinin induced a concentration-dependent increase in ouabain-sensitive Rb-86' uptake with an EC50 of 6 nM (pD(2) = 8.21 +/-0.20). 4 The B-1 receptor antagonist des-Arg(10)-HOE 140 (1 muM) had no effect on bradykinin-stimulated ouabain-sensitive Rb-86(+) uptake. The B-2 receptor antagonists HOE 140 and WIN 64338 antagonized bradykinin-stimulated ouabain-sensitive Rb-86(+) uptake with pK(B) values (-log M) of 8.20 +/-0.08 and 8.11 +/-0.20 respectively. 5 Reducing extracellular Na+ from 146 mM to 11 mM caused a 53.5% decrease in basal ouabain-sensitive Rb-86(+) uptake and abolished bradykinin-induced uptake. Two inhibitors of the Na+-H+ exchanger, methylisobutyl-amiloride (MIA; 1-100 muM) and ethylisopropyl-amiloride (EIPA; 0.1-10 muM), inhibited bradykinin-stimulated ouabain-sensitive Rb-86(+) uptake without affecting basal uptake. 6 These results suggest that bradykinin increases Na+-K+ pump activity of guinea-pig tracheal smooth muscle via stimulation of B-2 receptors and activation of the Na+-H+ exchanger.