A new look at sodium channel β subunits.

Voltage-gated sodium (Nav) channels are intrinsic plasma membrane proteins that initiate the action potential in electrically excitable cells. They are a major focus of research in neurobiology, structural biology, membrane biology and pharmacology. Mutations in Nav channels are implicated in a wide variety of inherited pathologies, including cardiac conduction diseases, myotonic conditions, epilepsy and chronic pain syndromes. Drugs active against Nav channels are used as local anaesthetics, anti-arrhythmics, analgesics and anti-convulsants. The Nav channels are composed of a pore-forming α subunit and associated β subunits. The β subunits are members of the immunoglobulin (Ig) domain family of cell-adhesion molecules. They modulate multiple aspects of Nav channel behaviour and play critical roles in controlling neuronal excitability. The recently published atomic resolution structures of the human β3 and β4 subunit Ig domains open a new chapter in the study of these molecules. In particular, the discovery that β3 subunits form trimers suggests that Nav channel oligomerization may contribute to the functional properties of some β subunits

Expression of phosphorylated Pyk2 in FAK+/+ and FAK−/− osteoblasts.

<p>Expression and localization of phosphorylated Pyk2 at Tyr-402 (red) in FAK+/+ (A) and FAK−/− (B) osteoblasts. DAPI nuclei stain in blue. Magnification = 60×. Scale bar represents 25 µm.</p

Trabecular Microarchitecture in the Distal Femur of Adult WT and FAK−/− Mice.

<p>Mean ± SD; <i>n</i>, sample number; BV/TV, bone volume; Tb.N, trabecular number; Tb.Th, trabecular thickness; Tb.Sp, trabecular spacing; Conn.D, connectivity density; SMI, structure model index; ^a<i>p</i><0.05 versus gender-matched WT group.</p

Structural Properties of the Femur in WT and FAK−/− Adult Mice.

<p>Mean ± SD; <i>n</i>, sample number; I_MAX, maximum second moment of area; I_MIN, minimum second moment of area; Ct.Ar, cortical area; Ct.Th, cortical thickness; ^a<i>p</i><0.05 versus gender-matched WT group.</p

Focal adhesion formation and actin cytoskeleton in wild-type and FAK−/− osteoblasts.

<p>(A–C) FAK+/+ osteoblasts form focal adhesions (red) as shown by vinculin staining and display prominent actin fiber formation (green) as shown by phalloidin staining. (D–F) FAK−/− osteoblasts also exhibit actin fiber and focal adhesion formation. Panels C and F show merged images. DAPI nuclei stain in blue. Magnification = 60×. Scale bar represents 25 µm.</p

Transverse cross-sections at ulnar midshaft in nonloaded (left) and loaded (right) forearms in WT (top) and FAK−/− (bottom) mice given calcein (green) and alizarin (red) fluorochrome bone labels at 4 and 11 days, respectively, after the first day of loading.

<p>In response to applied mechanical loading, most new bone is formed on the medial and lateral surfaces where bending strains are highest. Note the appearance of double bone labels (green and red) on the medial and lateral surfaces of the ulna, as well as on the rostral surface, in the loaded ulna (top, right) compared to the nonloaded internal control (top, left) where very little bone formation is observed. The loaded ulna (bottom, right) in FAK−/− mice exhibit bone formation on the medial and lateral ulnar surfaces, but much less new bone formation, in terms of percent mineralizing surface, is observed relative to the nonloaded ulna (bottom, left). Sections are representative of the response observed for WT and FAK−/− mice. Magnification = 10×.</p

Relative bone formation parameters in WT and FAK−/− male and female mice.

<p>Conditional deletion of FAK did not affect relative mineralizing surface (rMS/BS), relative mineral apposition rate (rMAR) or relative bone formation rate (rBFR/BS), which is a product of rMS/BS and rMAR. Data are presented as box and whisker plots where the median, Q2, Q3 and whiskers, representing the 5% and 95% confidence intervals, are depicted.</p

Rodent ulnar loading model.

<p>The right forearm in mice is subjected to cycle axial compression across the olecranon and flexed carpus while under isoflurane anesthesia. Due to the natural curvature of the ulna-radius complex in the medial direction, compressive loading creates a bending moment about the craniocaudal axis creating compressive and tensile bending strains on the medial and lateral surfaces, respectively.</p