Electrically stimulated Krebs-Henseleit buffer does not relax precontracted human bronchi in vitro

Electric field stimulation (EFS) causes a non-adrenergic relaxation of precontracted human airways. Only 10-20% of this response can be blocked with the nervous conductance blocker tetrodotoxin (TTX). Therefore, 80-90% of the non-adrenergic relaxation is not neurally mediated. The mechanism of this non-neural component is unclear. We examined whether EFS induces the generation of muscle relaxing substances in oxygenated Krebs-Henseleit buffer. Strips of central airways of 6 patients were precontracted with methacholine (10(-5) M) and exposed to Krebs buffer that had previously been stimulated with EFS (50 V, 0.3 ms, 30 s, 1-50 Hz). Results were compared to those obtained with unstimulated buffer. The contractile state of the airways did not change significantly with either EFS-stimulated or unstimulated buffer. We conclude that in oxygenated Krebs buffer EFS does not cause generation of substances that change the contractile state of prestimulated human airways.