Spinal cord injury: association with axonal peripheral neuropathy in severely paralysed limbs.

BACKGROUND AND PURPOSE: Pressure sores are a major health problem in spinal cord injury (SCI). In this population pressure damage to peripheral nerves was not thoroughly investigated so far. However, intact peripheral nerves and innervated muscles are a prerequisite for the effectiveness of supportive therapies like functional electrical stimulation (FES). METHODS: We assessed electroneurographic (ENG) data of lower limbs in SCI individuals admitted to our hospital due to severe pressure sores. Our centers prospectively acquired ENG data of the European Multicenter study about SCI (EMSCI) patients served as early control. RESULTS: In the pressure sore cohort (n = 15) all patients were sensory-motor complete (American Spinal Cord Injury Association Impairment Scale A). Most patients (10/15) suffered from a severe axonal sensory-motor polyneuropathy in paralysed legs with absent compound muscle action potentials (CMAPs) of tibial/peroneal nerves as well as absent sensory nerve action potentials of sural nerves. The onset of this polyneuropathy dates within the first year after incident SCI and was mainly associated with increasing sensory-motor completeness as demonstrated by a significant CMAP drop of our centers EMSCI-ENG data on serial tibial nerve recordings in 275 patients. CONCLUSIONS: Severe SCI is associated with an early-onset axonal polyneuropathy in paralysed limbs to which pressure damage might contribute. Because intact peripheral nerves are required for: (i) maintenance of motor function in centrally impaired muscles; and (ii) effectiveness of supportive therapies like FES, ENG-monitoring could serve as a low invasive screening method for peripheral nerve integrity in patients with SCI to initiate pressure relief procedures early enough.

Control of epithelial ion transport by Cl- and PDZ proteins.

Inhibition of epithelial Na+ channels (ENaC) by the cystic fibrosis transmembrane conductance regulator (CFTR) has been demonstrated previously. Recent studies suggested a role of cytosolic Cl- for the interaction of CFTR with ENaC, when studied in Xenopus oocytes. In the present study we demonstrate that the Na+ / H+ -exchanger regulator factor (NHERF) controls expression of CFTR in mouse collecting duct cells. Inhibition of NHERF largely attenuates CFTR expression, which is paralleled by enhanced Ca(2+) -dependent Cl- secretion and augmented Na+ absorption by the ENaC. It is further demonstrated that epithelial Na+ absorption and ENaC are inhibited by cytosolic Cl- and that stimulation by secretagogues enhances the intracellular Cl- concentration. Thus, the data provide a clue to the question, how epithelial cells can operate as both absorptive and secretory units: Increase in intracellular Cl- during activation of secretion will inhibit ENaC and switch epithelial transport from salt absorption to Cl- secretion.

Electrolyte transport in the mouse trachea: no evidence for a contribution of luminal K(+) conductance.

Recent studies on frog skin acini have challenged the question whether Cl(-) secretion or Na(+) absorption in the airways is driven by luminal K(+) channels in series to a basolateral K(+) conductance. We examined the possible role of luminal K(+) channels in electrolyte transport in mouse trachea in Ussing-chamber experiments. Tracheas of both normal and CFTR (-/-) mice showed a dominant amiloride-sensitive Na+ absorption under both, control conditions and after cAMP-dependent stimulation. The lumen-negative transepithelial voltage was enhanced after application of IBMX and forskolin and Cl(-) secretion was activated. Electrolyte secretion induced by IBMX and forskolin was inhibited by luminal glibenclamide and the blocker of basolateral Na(+2)Cl(-)K(+) cotransporter azosemide. Similarly, the compound 293B, a blocker of basolateral KCNQ1/KCNE3 K(+) channels effectively blocked Cl(-) secretion when applied to either the luminal or basolateral side of the epithelium. RT-PCR analysis suggested expression of additional K(+) channels in tracheal epithelial cells such as Slo1 and Kir6.2. However, we did not detect any functional evidence for expression of luminal K(+) channels in mouse airways, using luminal 293B, clotrimazole and Ba(2+) or different K(+) channel toxins such as charybdotoxin, apamin and a-dendrotoxin. Thus, the present study demonstrates Cl(-) secretion in mouse airways, which depends on basolateral Na(+2)Cl(-)K(+) cotransport and luminal CFTR and non-CFTR Cl(-) channels. Cl(-) secretion is maintained by the activity of basolateral K(+) channels, while no clear evidence was found for the presence of a luminal K(+) conductance.