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

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Abstract
The effect of bradykinin on the Na+‐K+ pump of airway smooth muscle was investigated by measuring ouabain‐sensitive 86Rb+ uptake in cultured guinea‐pig tracheal smooth muscle cells. Bradykinin induced a concentration‐dependent increase in ouabain‐sensitive 86Rb+ uptake, with an EC50 of 3 nM (pD2=8.50±0.10). Stimulation was not affected by indomethacin (1 μM) suggesting that it is not mediated by cycloxygenase products of arachidonic acid. The B1 receptor agonists Lys‐des‐Arg9‐bradykinin and des‐Arg9‐bradykinin had no effect on ouabain‐sensitive 86Rb+ uptake. In contrast, the B1 and B2 receptor agonist Lys‐bradykinin induced a concentration‐dependent increase in ouabain‐sensitive 86Rb+ uptake with an EC50 of 6 nM (pD2=8.21±0.20). The B1 receptor antagonist des‐Arg10‐HOE 140 (1 μM) had no effect on bradykinin‐stimulated ouabain‐sensitive 86Rb+ uptake. The B2 receptor antagonists HOE 140 and WIN 64338 antagonized bradykinin‐stimulated ouabain‐sensitive 86Rb+ uptake with pKB values (−log M) of 8.20±0.08 and 8.11±0.20 respectively. Reducing extracellular Na+ from 146 mM to 11 mM caused a 53.5% decrease in basal ouabain‐sensitive 86Rb+ uptake and abolished bradykinin‐induced uptake. Two inhibitors of the Na+‐H+ exchanger, methylisobutyl‐amiloride (MIA; 1–100 μM) and ethylisopropyl‐amiloride (EIPA; 0.1–10 μM), inhibited bradykinin‐stimulated ouabain‐sensitive 86Rb+ uptake without affecting basal uptake. These results suggest that bradykinin increases Na+‐K+ pump activity of guinea‐pig tracheal smooth muscle via stimulation of B2 receptors and activation of the Na+‐H+ exchanger. British Journal of Pharmacology (2001) 133, 1339–1345; doi:10.1038/sj.bjp.0704198