NONADRENERGIC NONCHOLINERGIC NERVE-MEDIATED INHIBITORY CONTROL OF PIGEON ESOPHAGEAL MUSCLE

Pigeon oesophageal smooth muscle in vitro has spontaneous electromecha nical activity. In the presence of atropine and guanethidine, electric al field stimulation evokes a transient TTX-sensitive response compris ing inhibition of electric bursting activity and muscular relaxation. This NANC inhibitory response was analysed using the K+ channel blocke rs TEA and apamin. TEA perfusions (0.1-5 mM) induced a concentration-d ependent reduction in amplitude of EFS-evoked relaxation. Responses to higher stimulation frequencies were more sensitive to TEA than those to lower ones. The maximum reduction in amplitude (29% of control) was obtained on 30 Hz EFS evoked responses during 5 mM TEA perfusion. In a similar way, apamin (0.01-10 mu M) perfusion reduced NANC relaxation , up to 30% of control. These relaxation suggest that in the pigeon oe sophagus, NANC intramural neurons are responsible for muscular relaxat ion. We speculate that an increase in K+ conductance might be the main mechanism involved, although the residual response after K+ channel b lockade indicates the existence of an additional ionic mechanism.