Cloning, distribution and functional analysis of the type III sodium channel from human brain

Abstract

The type III voltage-gated sodium channel was cloned from human brain. The full-length cDNA has 89% identity with rat type III, and the predicted protein (1951 amino acids) has 55 differences. The expression pattern of human type III mRNA was determined in adult brain tissue and, in contrast to rat, was detected in many regions, including caudate nucleus, cerebellum, hippocampus and frontal lobe. The human type III channel was stably expressed in Chinese hamster ovary (CHO) cells and its biophysical properties compared to the human type II channel using identical conditions. The voltage dependence and kinetics of activation were found to be similar to that of type II. The kinetics of inactivation of the two human subtypes were also similar. However, type III channels inactivated at more hyperpolarized potentials and were slower to recover from inactivation than type II. When expressed in human embryonic kidney (HEK293T) cells, type III channels produced currents with a prominent persistent component, which were similar to those reported for rat type II [Ma et al. (1997) Neuron, 19, 443-452]. However, unlike type II, this was prominent even in the absence of coexpressed G-proteins, suggesting type III may adopt this gating mode more readily. The distinct properties of the channel, together with its wide distribution in adult brain, suggest that in humans, type III may have important physiological roles under normal, and perhaps also pathological conditions.

Effects in Neocortical Neurons of Mutations of the Nav1.2 Na+Channel causing Benign Familial Neonatal-Infantile Seizures

“…This variability can be at least in part attributable to the high sensitivity to the cell milieu of Na ϩ channel properties (Baroudi et al, 2000;Chen et al, 2000;Cummins et al, 2001;Mantegazza et al, 2005b). We used transfected neocortical neurons in primary cultures because they provide an expression system that makes it possible to study exogenous channels while preserving neuronal properties, background, and variety.…”

“…The comparative study of the functional effects and the elucidation of the pathogenic mechanisms of epileptogenic mutations is essential for designing targeted and effective therapies for familial epilepsies. However, the functional analysis of Na ϩ channel mutations has generated controversial results, because the functional properties of Na ϩ channels are very sensitive to the cell back-ground and also the effects of pathogenic mutations are dependent on the expression system used (Baroudi et al, 2000;Chen et al, 2000;Cummins et al, 2001;Mantegazza et al, 2005b). To study BFNIS mutations with an experimental model that preserves neuronal properties and variety, we recorded Na ϩ currents in transfected neocortical neurons maintained for short time periods in primary cultures.…”

Model systems for studying cellular mechanisms ofSCN1A-related epilepsy

“…For example, cDNA encoding the human Na V 1.3 protein produces sodium channels that give rise to sodium currents with both a transient and a persistent component when expressed in HEK cells. This same sequence expressed in CHO cells results in sodium currents with only a transient component (Chen et al 2000). The mechanism for the difference in persistent currents between cell types is not yet clear.…”

Molecular and functional differences in voltage-activated sodium currents between GABA projection neurons and dopamine neurons in the substantia nigra

“…Additionally, Na V channels also conduct a small but long-lasting or persistent Na current (I NaP ) that increases neuronal excitability and promotes pacemaking firing (Bean 2007;Crill 1996). mRNAs for Na V 1.1, Na V 1.2, Na V 1.3, and Na V 1.6 ␣-subunits, Na V ␤3 and Na V ␤4 ␤-subunits, and also Na V 1.1 and N V 1.2 ␣-subunit proteins have been detected in the nigral region (Burbidge et al 2002;Chen et al 2000;Furuyama et al 1993;Gong et al 1999;Morgan et al 2000; Yu et al 2003). Furthermore, mRNA for Na V ␤4, a key ␤-subunit for Na V channels with resurgent kinetics, is expressed at a high level in the SNr but not in SNc (Yu et al 2003).…”