THE SEARCH FOR PREJUNCTIONAL INHIBITORY MUSCARINIC RECEPTORS IN HUMANBRONCHUS

The purpose of our study was to search for and classify prejunctional inhibitory muscarinic receptors in human bronchus with a wide range of muscarinic antagonists. Human bronchial airway smooth muscle strips, collected at thoracotomy from 54 subjects, 31 patients with chronic ai rway obstruction and 23 control subjects, were suspended in organ bath s and stimulated by electrical field stimulation. The stimulation para meters were: frequency: 32 Hz; Grass reading voltage: 70 V (voltage be tween the electrodes: 15 V); pulse duration: 0.5 msec and train durati on: 10 sec, every minute. Twitch responses of smooth muscle strips of 27 subjects (14 with and 13 without chronic airway obstruction) were s ufficiently stable to search for the effects of M1-, M2- and M3-select ive antagonists. All antagonists were added to the bath in a cumulativ e manner and decreased twitch contraction. No convincing evidence was found for the presence of prejunctional inhibitory muscarinic receptor s of the M2-subtype, reasons for this obvious absence are discussed. A naesthetical drugs for example, may mask the prejunctional inhibitory muscarinic receptors. The question remains whether the used electrical field stimulation experiments are suitable to point out prejunctional inhibitory muscarinic receptors. It is concluded that additional expe riments with other experimental methods and in patients with different anaesthetical treatment are needed.