Activation of endothelial and epithelial KCa2.3 calcium-activated potassium channels by NS309 relaxes human small pulmonary arteries and bronchioles

BACKGROUND AND PURPOSE Small (KCa2) and intermediate (KCa3.1) conductance calcium-activated potassium channels (KCa) may contribute to both epithelium- and endothelium-dependent relaxations, but this has not been established in human pulmonary arteries and bronchioles. Therefore, we investigated the expression of KCa2.3 and KCa3.1 channels, and hypothesized that activation of these channels would produce relaxation of human bronchioles and pulmonary arteries. EXPERIMENTAL APPROACH Channel expression and functional studies were conducted in human isolated small pulmonary arteries and bronchioles. KCa2 and KCa3.1 currents were examined in human small airways epithelial (HSAEpi) cells by whole-cell patch clamp techniques. RESULTS While KCa2.3 expression was similar, KCa3.1 protein was more highly expressed in pulmonary arteries than bronchioles. Immunoreactive KCa2.3 and KCa3.1 proteins were found in both endothelium and epithelium. KCa currents were present in HSAEpi cells and sensitive to the KCa2.3 blocker UCL1684 and the KCa3.1 blocker TRAM-34. In pulmonary arteries contracted by U46619 and in bronchioles contracted by histamine, the KCa2.3/ KCa3.1 activator, NS309, induced concentration-dependent relaxations. NS309 was equally potent in relaxing pulmonary arteries, but less potent in bronchioles, than salbutamol. NS309 relaxations were blocked by the KCa2 channel blocker apamin, while the KCa3.1 channel blocker, charybdotoxin failed to reduce relaxation to NS309 (0.011 mu M). CONCLUSIONS AND IMPLICATIONS KCa2.3 and KCa3.1 channels are expressed in the endothelium of human pulmonary arteries and epithelium of bronchioles. KCa2.3 channels contributed to endo- and epithelium-dependent relaxations suggesting that these channels are potential targets for treatment of pulmonary hypertension and chronic obstructive pulmonary disease.