Urothelial Tight Junction Barrier Dysfunction Sensitizes Bladder Afferents
Authors: Montalbetti, Nicolas; Rued, Anna C.; Taiclet, Stefanie N.; Birder, Lori A.; Kullmann, F. Aura; Carattino, Marcelo D.
Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic voiding disorder that presents with pain in the urinary bladder and surrounding pelvic region. A growing body of evidence suggests that an increase in the permeability of the urothelium, the epithelial barrier that lines the interior of the bladder, contributes to the symptoms of IC/BPS. To examine the consequence of increased urothelial permeability on pelvic pain and afferent excitability, we overexpressed in the urothelium claudin 2 (Cldn2), a tight junction (TJ)-associated protein whose message is significantly upregulated in biopsies of IC/BPS patients. Consistent with the presence of bladder-derived pain, rats overexpressing Cldn2 showed hypersensitivity to von Frey filaments applied to the pelvic region. Overexpression of Cldn2 increased the expression of c-Fos and promoted the activation of ERK1/2 in spinal cord segments receiving bladder input, which we conceive is the result of noxious stimulation of afferent pathways. To determine whether the mechanical allodynia observed in rats with reduced urothelial barrier function results from altered afferent activity, we examined the firing of acutely isolated bladder sensory neurons. In patch-clamp recordings, about 30% of the bladder sensory neurons from rats transduced with Cldn2, but not controls transduced with GFP, displayed spontaneous activity. Furthermore, bladder sensory neurons with tetrodotoxin-sensitive (TTX-S) action potentials from rats transduced with Cldn2 showed hyperexcitability in response to suprathreshold electrical stimulation. These findings suggest that as a result of a leaky urothelium, the diffusion of urinary solutes through the urothelial barrier sensitizes bladders afferents, promoting voiding at low filling volumes and pain.
A Novel Toxin from Haplopelma lividum Selectively Inhibits the Na(V)1.8 Channel and Possesses Potent Analgesic Efficacy
Authors: Meng, Ping; Huang, Honggang; Wang, Gan; Yang, Shilong; Lu, Qiuming; Liu, Jingze; Lai, Ren; Rong, Mingqiang
Spider venoms are a complex mixture of peptides with a large number of neurotoxins targeting ion channels. Although thousands of peptide toxins have been identified from venoms of numerous species of spiders, many unknown species urgently need to be investigated. In this study, a novel sodium channel inhibitor, mu-TRTX-Hl1a, was identified from the venom of Haplopelma lividum. It contained eight cysteines and formed a conserved cysteine pattern of ICK motif. mu-TRTX-Hl1a inhibited the TTX-resistant (TTX-r) sodium channel current rather than the TTX-sensitive (TTX-s) sodium channel current. Meanwhile, mu-TRTX-Hl1a selectively inhibited Na(V)1.8 with an IC50 value of 2.19 mu M. Intraperitoneal injection of mu-TRTX-Hl1a dose-dependently reduced inflammatory and neuropathic pain in rodent models of formalin-induced paw licking, tail-flicking, acetic acid-induced writhing, and hot plate test. It showed a better analgesic effect than morphine in inflammatory pain and equipotent effect to morphine in neuropathic pain. These findings demonstrate that mu-TRTX-Hl1a might be a valuable tool for physiology studies on Na(V)1.8 and a promising lead molecule for pain therapeutics.