Ongoing pain has been linked to ongoing activity (OA) in human C-fiber nociceptors, but rodent models of pain-related OA have concentrated on allodynia rather than ongoing pain, and on OA generated in non-nociceptive Aβ fibers rather than C-fiber nociceptors. Little is known about how ongoing pain or nociceptor OA is generated. To define neurophysiological alterations underlying nociceptor OA, we have used isolated dorsal root ganglion neurons that continue to generate OA after removal from animals displaying ongoing pain. We subclassify OA as either spontaneous activity generated solely by alterations intrinsic to the active neuron or as extrinsically driven OA. Both types of OA were implicated previously in nociceptors in vivo and after isolation following spinal cord injury, which produces chronic ongoing pain. Using novel automated algorithms to analyze irregular changes in membrane potential, we have found, in a distinctive, nonaccommodating type of probable nociceptor, induction by spinal cord injury of 3 alterations that promote OA: (1) prolonged depolarization of resting membrane potential, (2) a hyperpolarizing shift in the voltage threshold for action potential generation, and (3) an increase in the incidence of large depolarizing spontaneous fluctuations (DSFs). Can DSFs also be enhanced acutely to promote OA in neurons from uninjured animals? A low dose of serotonin failed to change resting membrane potential but lowered action potential threshold. When combined with artificial depolarization to model inflammation, serotonin also strongly potentiated DSFs and OA. These findings reveal nociceptor specializations for generating OA that may promote ongoing pain in chronic and acute conditions.

Recent cloning of a cold/menthol-sensitive TRPM8 channel (transient receptor potential melastatine family member 8) from rodent sensory neurons has provided the molecular basis for the cold sensation. Surprisingly, the human orthologue of rodent TRPM8 also appears to be strongly expressed in the prostate and in the prostate cancer-derived epithelial cell line, LNCaP. In this study, we show that despite such expression, LNCaP cells respond to cold/menthol stimulus by membrane current (I cold/menthol ) that shows inward rectification and high Ca 2؉ selectivity, which are dramatically different properties from "classical" TRPM8-mediated I cold/menthol . Yet, silencing of endogenous TRPM8 mRNA by either antisense or siRNA strategies suppresses both I cold/menthol and TRPM8 protein in LNCaP cells. We demonstrate that these puzzling results arise from TRPM8 localization not in the plasma, but in the endoplasmic reticulum (ER) membrane of LNCaP cells, where it supports cold/menthol/icilin-induced Ca 2؉ release from the ER with concomitant activation of plasma membrane (PM) store-operated channels (SOC). In contrast, GFP-tagged TRPM8 heterologously expressed in HEK-293 cells target the PM. We also demonstrate that TRPM8 expression and the magnitude of SOC current associated with it are androgen-dependent. Our results suggest that the TRPM8 may be an important new ER Ca 2؉ release channel, potentially involved in a number of Ca 2؉ -and store-dependent processes in prostate cancer epithelial cells, including those that are important for prostate carcinogenesis, such as proliferation and apoptosis. Mammalian homologues of the Drosophila transient receptor potential (TRP)7 channel, which initially emerged as a channel specifically linked to phospholipase C-catalyzed inositol phospholipid breakdown signaling pathways, have now grown into a broad family of channelforming proteins displaying extraordinarily diverse activation mechanisms (for reviews, see Refs. 1-5). At present, these channels are grouped into six subfamilies based on structural homology and have been given a standard nomenclature (5).A number of mammalian TRPs show a unique mode of gating, in response to thermal stimuli as well as to the chemical imitators of burning and cooling sensations, capsaicin and menthol, respectively. As such, they represent a group of thermal receptors covering a wide range of physiological temperatures. Most thermal receptors belong to the vanilloid TRP subfamily (TRPV, Ref. 6) including warm-sensitive (Ͻ40°C) TRPV3 (7-9) and heat-and capsaicin-sensitive TRPV1 (Ͼ43°C) (10) and TRPV2 (Ͼ52°C) (11). In contrast, sensitivity to cooling temperatures (Ͻ22°C) and menthol is mediated by a structurally distant thermal receptor, TRPM8, belonging to the melastatine (TRPM) subfamily of TRP channels (12, 13); the ankyrin transmembrane protein 1 (ANKTM1 or TRPA1) is involved in the detection of noxious cold (14).Consistent with their role in the sensation of distinct physiological temperatures, thermal receptors are mostly expressed in subsets of...

Accumulating data point to K þ channels as relevant players in controlling cell cycle progression and proliferation of human cancer cells, including prostate cancer (PCa) cells. However, the mechanism(s) by which K þ channels control PCa cell proliferation remain illusive. In this study, using the techniques of molecular biology, biochemistry, electrophysiology and calcium imaging, we studied the expression and functionality of intermediate-conductance calcium-activated potassium channels (IK Ca1 ) in human PCa as well as their involvement in cell proliferation. We showed that IK Ca1 mRNA and protein were preferentially expressed in human PCa tissues, and inhibition of the IK Ca1 potassium channel suppressed PCa cell proliferation. The activation of IK Ca1 hyperpolarizes membrane potential and, by promoting the driving force for calcium, induces calcium entry through TRPV6, a cation channel of the TRP (Transient Receptor Potential) family. Thus, the overexpression of the IK Ca1 channel is likely to promote carcinogenesis in human prostate tissue.