The Nav1.9 channel is a key determinant of cold pain sensation and cold allodynia

Cold-triggered pain is essential to avoid prolonged exposure to harmfully low temperatures. However, the molecular basis of noxious cold sensing in mammals is still not completely understood. Here, we show that the voltage-gated Nav1.9 sodium channel is important for the perception of pain in response to noxious cold. Nav1.9 activity is upregulated in a subpopulation of damage-sensing sensory neurons responding to cooling, which allows the channel to amplify subthreshold depolarizations generated by the activation of cold transducers. Consequently, cold-triggered firing is impaired in Nav1.9(-/-) neurons, and Nav1.9 null mice and knockdown rats show increased cold pain thresholds. Disrupting Nav1.9 expression in rodents also alleviates cold pain hypersensitivity induced by the antineoplastic agent oxaliplatin. We conclude that Nav1.9 acts as a subthreshold amplifier in cold-sensitive nociceptive neurons and is required for the perception of cold pain under normal and pathological conditions.

Menthol pain relief through cumulative inactivation of voltage-gated sodium channels

Menthol is a natural compound of plant origin known to produce cool sensation via the activation of the TRPM8 channel. It is also frequently part of topical analgesic drugs available in a pharmacy, although its mechanism of action is still unknown. Compelling evidence indicates that voltage-gated Na(+) channels are critical for experiencing pain sensation. We tested the hypothesis that menthol may block voltage-gated Na(+) channels in dorsal root ganglion (DRG) neurons. By use of a patch clamp, we evaluated the effects of menthol application on tetrodotoxin (TTX)-resistant Nav1.8 and Nav1.9 channel subtypes in DRG neurons, and on TTX-sensitive Na(+) channels in immortalized DRG neuron-derived F11 cells. The results indicate that menthol inhibits Na(+) channels in a concentration-, voltage-, and frequency-dependent manner. Menthol promoted fast and slow inactivation states, causing use-dependent depression of Na(+) channel activity. In current clamp recordings, menthol inhibited firing at high-frequency stimulation with minimal effects on normal neuronal activity. We found that low concentrations of menthol cause analgesia in mice, relieving pain produced by a Na(+) channel-targeting toxin. We conclude that menthol is a state-selective blocker of Nav1.8, Nav1.9, and TTX-sensitive Na(+) channels, indicating a role for Na(+) channel blockade in the efficacy of menthol as topical analgesic compound.

A polycystin-2 (TRPP2) dimerization domain essential for the function of heteromeric polycystin complexes

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in two genes, PKD1 and PKD2, which encode polycystin-1 (PC1) and polycystin-2 (PC2), respectively. Earlier work has shown that PC1 and PC2 assemble into a polycystin complex implicated in kidney morphogenesis. PC2 also assembles into homomers of uncertain functional significance. However, little is known about the molecular mechanisms that direct polycystin complex assembly and specify its functions. We have identified a coiled coil in the C-terminus of PC2 that functions as a homodimerization domain essential for PC1 binding but not for its self-oligomerization. Dimerization-defective PC2 mutants were unable to reconstitute PC1/PC2 complexes either at the plasma membrane (PM) or at PM-endoplasmic reticulum (ER) junctions but could still function as ER Ca(2+)-release channels. Expression of dimerization-defective PC2 mutants in zebrafish resulted in a cystic phenotype but had lesser effects on organ laterality. We conclude that C-terminal dimerization of PC2 specifies the formation of polycystin complexes but not formation of ER-localized PC2 channels. Mutations that affect PC2 C-terminal homo- and heteromerization are the likely molecular basis of cyst formation in ADPKD.

[Computerized tomography assessment of bone damage following injury of the anterior cruciate ligament]

An ACL tear causes an anterior subluxation of the tibial bone which rotates with its fulcrum on the medial collateral ligament; consequently, the lateral femoral condyle impacts on the external tibial plateau. The presence of a subcortical lesion of the spongiform bone in the posterior external tibial plateau is an indirect sign of an ACL tear. On MR images, traumatic changes are depicted as changes in bone marrow signals. To assess the diagnostic capabilities of CT in demonstrating the bone lesion subsequent to ACL trauma, 23 patients with positive MR exams of the knee were submitted to CT. Fifteen patients had complete ACL tears, 8 had partial tears and 20 exhibited an occult fracture of the posterior portion of the external tibial plateau. This study pointed out a significant correlation between ACL tears and changes in the spongiform structure of the posterolateral tibial plateau. Such changes are depicted not only by MRI but also by CT: the latter method is also a valuable tool to study these conditions long after the traumatic event. No more than 5 slices, 1-1.5 mm thick, acquired at the tibial plateau allowed the trabecular structure and its abnormal changes to be studied without markedly lengthening examination time.

[Impingement syndrome of the shoulder. Clinical data and radiologic findings]

Subcoracoid impingement syndrome pain is elicited by some positions of the upper limbs, i.e., adduction and inward rotation, whenever coracohumeral space reduces. Although acquired or congenital malformations of the humeral head and/or coracoid apophysis are the most common causes of painful syndromes, repeated flections and inward rotations of the upper limbs, typical of some sports, such as swimming and tennis, and of some sports, such as swimming and tennis, and of some kinds of work, are predisposing factors. The subcoracoid impingement syndrome exhibits on pathogenomonic signs at clinics and the specificity of diagnostic methods is low, which calls for reliable radiologic assessment of this condition. Fifteen patients with subcoracoid impingement syndrome underwent X-ray, US, CT and MR studies. Plain radiography detected no specific signs of this syndrome, but yielded useful information regarding other painful syndromes of the shoulder, such as anatomical variants of the acromion and degenerative changes. US yield was poor because of the acoustic window of the coracoid apophysis, but supraspinatus tendon changes were demonstrated in 2 cases. CT and MRI proved to be the most reliable and accurate diagnostic methods, the former thanks to its sensitivity to even slight bone changes and to its capabilities in measuring coracohumeral distance and acquiring dynamic scans and the latter because it detects tendon, bursa and rotator cuff changes. To conclude, in our opinion, when the subcoracoid impingement syndrome is clinically suspected, plain X-ray films should be performed first and followed by MR scans.