Characterization of a novel SCN5A mutation associated with Brugada syndrome reveals involvement of DIIIS4-S5 linker in slow inactivation

OBJECTIVE: Mutations in SCN5A, the gene encoding the alpha-subunit of the cardiac sodium channel (Na(v)1.5), have been associated with various inherited arrhythmia syndromes, including Brugada syndrome (BrS). Here, we report the functional consequences of a novel missense SCN5A mutation, G1319V, identified in a BrS patient. The G1319V mutation is located in the loop connecting transmembrane segments 4 and 5 in domain III (DIIIS4-S5), a region so far considered to be exclusively involved in fast inactivation. METHODS: Whole-cell mutant (G1319V) and wild-type (WT) sodium currents (I(Na)) were studied in the Human Embryonic Kidney cell line (HEK-293) transfected with Na(v)1.5 alpha-subunit cDNA (WT or mutant) together with hbeta(1)-subunit cDNA, using the patch-clamp technique. RESULTS: Maximal peak I(Na) and persistent sodium current were similar in WT and channel G1319V channels. The G1319V mutation shifted the potential of half-maximal (V(1/2)) activation towards more positive potentials (+3.7 mV), thereby increasing the degree of depolarization required for activation. The V(1/2) of inactivation of G1319V channels was shifted by -6.0 mV compared to WT, resulting in a reduced channel availability. The change in the steady-state inactivation was completely due to a negative shift (-6.8 mV) of the voltage-dependence of slow inactivation, while the voltage-dependence of fast inactivation was unaffected. The fast component of recovery from inactivation of G1319V channels was slowed down. Finally, the G1319V mutation caused a two-fold increase in the propensity of the channels to enter the slow inactivated state. Reduction in I(Na) peak amplitude on repetitive depolarizations at short interpulse intervals (40 ms) was significantly more pronounced in G1319V compared to WT. Accordingly, carriers of the G1319V mutation showed marked QRS widening upon increases in heart rate during exercise testing, pointing to enhancement of slow inactivation. CONCLUSIONS: We identified the DIIIS4-S5 linker as a new region involved in slow inactivation of Na(v)1.5. The biophysical alterations of the G1319V mutation all contribute to a reduction in I(Na), in line with the proposed mechanism underlying BrS.     

Microtubule-associated protein tau as a therapeutic target in neurodegenerative disease

Interest in the biology of the microtubule-associated protein tau, not only as a pathologic marker, but as a therapeutic target has surged considerably over the last few years. This is due, in part, to the discovery of mutations in tau causing a group of aggressively degenerative neurologic disorders characterized by abnormalities of tau very similar to what is seen in Alzheimer's disease where mutations in tau are absent. As these same mutations also precipitate authentic forms of neurofibrillary degeneration in tau transgenic mice, the gateways to testing therapeutic ideas preclinically have opened. Other Alzheimer's disease animal models have been notoriously bare of this feature, limiting their predictive power for clinical success. In this review, the authors discuss some of the main therapeutic ideas presently advanced in the field and their molecular rationales.     

Autologous myoblasts and fibroblasts for female stress incontinence: a 1-year follow-up in 123 patients

OBJECTIVE: To assess the efficacy and safety of the application of autologous myoblasts and fibroblasts for treating female stress urinary incontinence (SUI) after a follow-up of >/=1 year. PATIENTS AND METHODS: In all, 123 women with SUI (aged 36-84 years) were treated with transurethral ultrasonography-guided injections with autologous myoblasts and fibroblasts obtained from skeletal muscle biopsies. The fibroblasts were suspended in a small amount of collagen as carrier material and injected into the urethral submucosa, while the myoblasts were implanted into the rhabdosphincter. All patients were evaluated before and 12 months after the injection using the Incontinence and Quality of Life Instrument (I-QOL) scores, urodynamic variables, and morphology and function of the urethra and rhabdosphincter. RESULTS: At 1 year after implanting the cells, 94 of the 119 women (79%) were completely continent, 16 (13%) had a substantial improvement and nine (8%) a slight improvement. Four patients were lost to follow-up.The incontinence and I-QOL scores, and the thickness, contractility and electromyographic activity of the rhabdosphincter were significantly improved after treatment. CONCLUSIONS: These results show the efficacy and safety of transferring autologous myoblasts and fibroblasts in the treatment of female SUI, after a follow-up of 1 year.     

Heparin--examination of its antibacterial adsorption properties

One of the primary antibacterial defense mechanisms of the bladder is the action of the luminal mucopolysaccharide layer against adsorption of inoculated bacteria. Previous studies have shown that local instillation of the mucopolysaccharide heparin can prevent bacterial adsorption on the bladder mucosa denuded of this "antiadherence factor." To determine whether this action was due to the mucopolysaccharide composition of heparin, or rather to its anticoagulant property, protamine sulfate (a basic protein with anticoagulant properties) was tested for antiadsorptive efficacy. Protamine offered no protection against bacterial adherence in the rabbit model. It appears that heparin's protective effect is unrelated to its action as an anticoagulant.