Intraganglionic laminar endings act as mechanoreceptors of vagal afferent nerve in guinea pig esophagus

Intraganglionic laminar endings (IGLEs) have been supposed to be the mechanoreceptors in the gut by electrophysiological recording techniques. But the specialized morphology of IGLEs could not be displayed closely associated with this function and the mechanism that IGLEs act as the mechanotransduction sites in the gut is not yet well understood. In the present study, we used styryl dye FM1-43 combined with stretch stimulation in the guinea pig esophagus to test whether IGLEs acted as the mechano-sensitive receptors of the vagal afferent nerves. At the same time, the special structure of IGLEs displayed by FM1-43 was further confirmed by neurobiotin anterograde labeling technique. To further investigate the characteristics of IGLEs as mechanosensitive receptors, different drugs were used to block or stimulate IGLEs activation. Our results indicated that only in the stretched preparation could FM1-43 enter the IGLEs and completely display their specialized structure, which was consistent with that shown by neurobiotin. The amount of IGLEs shown by stretch-evoked FM1-43 staining was much more than that shown without stretch stimulation [(90.4 +/- 9.5) % vs (10.7 +/- 2.1) %, P<0.05]. Ca(2+), TTX (0.6 mumol/L), atropine (0.6 mumol/L), SKF (50 mumol/L), and gadolium (100 mumol/L) had no effect on the IGLEs activation. But for benzamil (100 mumol/L), an epithelial sodium channel blocker, activation of IGLEs by stretch stimulation was significantly blocked. The potent ATP analogue, alpha,beta-methylene ATP (100 mumol/L) could not activate FM1-43 staining without stretch. These results indicate that IGLEs are sensitive to mechanical stimulation. This could lead to the deduction that IGLEs act as the mechanoreceptors of vagal afferent nerve. IGLEs could transmit mechanical stimuli directly through ion channels, independent of neurotransmitter release and action potential propagation. The stretch-sensitive channels on IGLEs probably belong to the epithelial sodium channel family rather than voltage-gated sodium ion channels. Furthermore, styryl dye FM1-43 is a useful activity-dependent marker to demonstrate the structure and function of IGLEs in guinea pig esophagus.