Immunohistochemical detection of ENaCβ in the terminal Schwann cells associated with the periodontal Ruffini endings of the rat incisor

Abstract

Epithelial sodium channels (ENaCs) are a subfamily of ion channels within the degenerin/ENaC (DEG/ENaC) superfamily. Previous studies have shown the immunolocalization of ENaC in the neural elements of the cutaneous mechanoreceptors as well as dorsal root and trigeminal ganglion neurons, indicating the involvement of this molecule in mechanotransduction. The present study examined the expression of ENaCβ, a major component of ENaC protein, in the mechanoreceptive Ruffini endings in the periodontal ligament of the rat incisors by immunohistochemistry. The expression of ENaCβ in the trigeminal ganglion-which innervates the periodontal Ruffini endings-was also investigated at the mRNA and protein levels. Furthermore, double staining and a nerve injury experiment were applied to clarify its detailed localization in the periodontal Ruffini endings. ENaCβ immunoreaction in the trigeminal ganglion was recognizable in the comparatively large neurons which have been considered to mediate mechanotransduction. Immunohistochemistry for ENaCβ demonstrated dendritic ramifications of the Ruffini endings as well as the rounded cells in the periodontal ligament. Double staining with ENaCβ and either PGP9.5 or S-100 protein showed immunoreaction for ENaCβ in both the axonal and glial elements in the periodontal ligament. Some ENaCβ positive cells with rounded profiles were reactive to non-specific cholinesterase activity. Furthermore, a transection of the inferior alveolar nerve failed to eliminate the rounded cells with ENaCβ reaction, indicating that they were the terminal Schwann cells associated with the periodontal Ruffini endings. These findings suggest that ENaCβ is a key mechanotransducing channel in the periodontal Ruffini endings. Probably, the terminal Schwann cells together with the axon terminals regulate mechanotransduction in the periodontal endings.Epithelial sodium channels (ENaCs) are members of the degenerin/ENaC (DEG/ENaC) family of voltage-insensitive, amiloride-blockable cation channels (21, 25). They are generally composed of four subunits: ENaCα, β, γ and δ. These ENaC subunits have a conserved topology consisting of two membrane-spanning domains with intracellular N-and C-termini and a large glycosylated extracellular region. Of these channels, a heterotetramer containing two ENaCα, one ENaCβ and one ENaCγ shows high sensitivity to amiloride and its analogues (21,25). However, the function of ENaCδ remains unknown though this subunit can also form a functional ion channel. Many studies have shown a wide distribution of ENaCs in various tissues where their expression at the apical membrane mediates unidirectional absorption of Na + (9, 15). These ENaCs can also be regarded as key mechanotransducing channels came from the findings that the mutation

Simultaneous Disruption of Mouse ASIC1a, ASIC2 and ASIC3 Genes Enhances Cutaneous Mechanosensitivity

“…It would be also interesting for future studies to investigate mechanically activated current in dissociate DRG neurons to characterize other mechanosensory phenotypes of ASIC TKO s. We have shown slower mean conduction velocity (CV) of Aδ-AMs from ASIC TKOs. Previous studies have demonstrated the expression of ASIC2 or other channels from DEG/ENaC superfamily by human or rat Schwann cells [56], [57]. Therefore, while the exact underlying mechanism remains unclear, warranting further investigation, this might suggest a possible role of ASIC s in Schwann cell function and axonal conduction in sub-populations of afferents.…”

Differential Localization of Acid-Sensing Ion Channels 1 and 2 in Human Cutaneus Pacinian Corpuscles

“…This was an unexpected finding, but not surprising, since ASIC2 has been also detected in satellite cells of the rat DRG (Kawamata et al 2006), and in the inner core cells of the murine Pacinian corpuscles . Furthermore, the expression of other proteins from the ASICs family was also detected in the Schwannrelated cells present in rat Ruffini endings (Hitomi et al 2009). …”

“…ASIC2a and ASIC3 are expressed in mechanoreceptors, including specialized cutaneous mechanosensory structures like Merkel nerve endings, palisades of lanceolate nerve endings, Meissner corpuscles, and Pacinian corpuscles (Garcia-Añoveros et al 2001;Price et al 2000Price et al , 2001Montaño et al 2009). Other members of the Deg/ ENaC family, like b-ENaC and c-ENaC, were also detected in different kinds of mechanoreceptors Montaño et al 2009;Hitomi et al 2009). Interestingly, the expression of Deg/ENaC in Pacinian corpuscles is differentially regulated by BDNF and NT-4 acting through TrkB ).…”

Blockade of ENaCs by amiloride induces c-Fos activation of the area postrema

“…This implies that the blockade of ENaCs on the salt taste receptors of the tongue (Chandrashekar et al, 2010) were surely not a factor that can explain the c-Fos labeling in the AP. A similar argument can be advanced regarding the ENaCs associated with the trigeminal nerve or its branches that innervate the teeth (Fricke et al, 2000; Hitomi et al, 2009). The amount of c-Fos labeling that occurred in the spinal trigeminal nucleus in amiloride-treated rats never exceeded the number of activated cells observed in the control animals.…”