Beschreibung
In various tissues cells have been detected that express components of the bitter taste signaling cascade and are thought to control host defense mechanisms as chemosensory sentinel cells. For example, it is assumed that bacterial metabolites indirectly influence the contraction of smooth muscle cells via activation of these bitter sensory cells.
Main functions of the epididymis are maturation, transport and storage of spermatozoa. The most distal part of the epididymal duct primarily stores spermatozoa until ejaculation. It does not show spontaneous contraction activity. Emission of spermatozoa is ensured by complex, noradrenaline-induced contractions of smooth muscle cells.
Since effects of bitter substances on contractions in the proximal, spontaneously contracting part of the epididymal duct have already been described, mouse tissue was used to investigate whether the bitter substance denatonium benzoate (DNT) also influences contractions of smooth muscles cells in the most distal part of the epididymal duct.
Live imaging was used to visualize and analyze potential effects. Hereby two different analyzing methods were compared. Reslice analyses were an opportunity to visualize the contraction frequency and changes in the diameter of the epididymal duct at single positions. Data of the second (multidirectional) movement analysis reflected and complemented reslice data. By this method it was possible to quantify complex contraction movements of the entire filmed tissue and to display them using heatmaps and graphs.
With regard to the effect of DNT, the following was shown: noradrenaline induced complex contractions in the most distal part of the epididymal duct, whereas DNT did not. Pretreatment with DNT prevented complex contractions by a subsequent noradrenaline treatment. DNT diminished ongoing contractions previously induced by noradrenaline and abolished the expected effect of a second noradrenaline treatment.
Components of the bitter taste signaling cascade could be identified by RT-PCR and immunofluorescence in wildtype mouse epididymis. The components were localized to epithelial cells. Statistical analyses of contractions in tissue with diminished bitter taste signaling showed that the inhibitory effect of DNT was decreased but still significant.
Thus, it is likely that DNT also modulates contraction via alternative pathways, different from bitter taste signaling, perhaps by direct interaction with smooth muscle cells. Overall, it can be hypothesized that contractile effects triggered by bacterial metabolites on various target cells significantly influence the course of an epididymal infection.
