Voltage-sensitive sodium channels and calcium channels are homologous proteins with distinctly different selectivity for permeation of inorganic cations. This difference in function is specified by amino acid residues located within P-region segments that link presumed transmembrane elements S5 and S6 in each of four repetitive Domains I, II, III, and IV. By analyzing the selective permeability of Na+, K+, and Ca2+ in various mutants of the mu 1 rat muscle sodium channel, the results in this paper support the concept that a conserved motif of four residues contributed by each of the Domains I-IV, termed the DEKA locus in sodium channels and the EEEE locus in calcium channels, determines the ionic selectivity of these channels. Furthermore, the results indicate that the Lys residue in Domain III of the sodium channel is the critical determinant that specifies both the impermeability of Ca2+ and the selective permeability of Na+ over K+. We propose that the alkylammonium ion of the Lys(III) residue acts as an endogenous cation within the ion binding site/selectivity filter of the sodium channel to tune the kinetics and affinity of inorganic cation binding within the pore in a manner analogous to ion-ion interactions that occur in the process of multi-ion channel conduction.

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is an uncommon, idiopathic partial epilepsy characterized by clusters of motor seizures occurring in sleep. We describe a mutation of the beta2 subunit of the nicotinic acetylcholine receptor, effecting a V287M substitution within the M2 domain. The mutation, in an evolutionary conserved region of CHRNB2, is associated with ADNFLE in a Scottish family. Functional receptors with the V287M mutation are highly expressed in Xenopus oocytes and characterized by an approximately 10-fold increase in acetylcholine sensitivity. CHRNB2 is a new gene for idiopathic epilepsy, the second acetylcholine receptor subunit implicated in ADNFLE.

Mutational and biophysical analysis suggests that an intracellular COOH-terminal domain of the large conductance Ca 2؉ -activated K ؉ channel (BK channel) contains Ca 2؉ -binding site(s) that are allosterically coupled to channel opening. However the structural basis of Ca 2؉ binding to BK channels is unknown. To pursue this question, we overexpressed the COOH-terminal 280 residues of the Drosophila slowpoke BK channel (Dslo-C280) as a FLAG-and His 6-tagged protein in Escherichia coli. We purified Dslo-C280 in soluble form and used a 45 Ca 2؉ -overlay protein blot assay to detect Ca 2؉ binding. Dslo-C280 exhibits specific binding of 45 Ca 2؉ in comparison with various control proteins and known EF-hand Ca 2؉ -binding proteins. A mutation (D5N5) of Dslo-C280, in which five consecutive Asp residues of the ''Ca-bowl'' motif are changed to Asn, reduces 45 Ca 2؉ -binding activity by 56%. By electrophysiological assay, the corresponding D5N5 mutant of the Drosophila BK channel expressed in HEK293 cells exhibits lower Ca 2؉ sensitivity for activation and a shift of Ϸ؉80 mV in the midpoint voltage for activation. This effect is associated with a decrease in the Hill coefficient (N) for activation by Ca 2؉ and a reduction in apparent Ca 2؉ affinity, suggesting the loss of one Ca 2؉ -binding site per monomer. These results demonstrate a functional correlation between Ca 2؉ binding to a specific region of the BK protein and Ca 2؉ -dependent activation, thus providing a biochemical approach to study this process.

Background and Purpose-Although neuroimaging studies have revealed specific patterns of reorganization in the sensorimotor control network after stroke, their role in recovery remains unsettled. To review the existing evidence systematically, we performed activation likelihood estimation meta-analysis of functional neuroimaging studies investigating upper limb movement-related brain activity after stroke. Methods-Twenty-four studies using sensorimotor tasks in standardized coordinates were included, totaling 255 patients and 145 healthy controls. Across the entire brain, we compared task-related activity patterns in good and poor recovery and assessed the magnitude of spatial shifts in sensorimotor activity in cortical motor areas after stroke. Results-When compared with healthy controls, patients showed higher activation likelihood estimation values in contralesional primary motor soon after stroke that abated with time, but were not related to motor outcome. The observed activity changes were consistent with restoration of typical interhemispheric balance. In contrast, activation likelihood estimation values in ipsilesional medial-premotor and primary motor cortex were associated with good outcome, reorganization that may reflect vicarious processes associated with ventral activity shifts from BA4a to 4p. In the anterior cerebellum, a novel finding was the association of poor recovery with increased vermal activity, possibly reflecting behaviorally inadequate compensatory strategies engaging the fastigio-thalamo-cortical and corticoreticulospinal systems. Conclusions-Activity in ipsilesional primary