Brain and heart sodium channel subtype mRNA expression in rat cerebral cortex.

Abstract

The expression of mRNAs coding for the a subunit of rat brain and rat heart sodium channels has been studied in adult and neonatal rat cerebral cortex using the reverse transcription-polymerase chain reaction (RT-PCR). Rat brain sodium channel subtype I, H, HA, and HI sequences were simultaneously amplified in the same PCR using a single oligonucleotide primer pair matched to all four subtype sequences. Identification of each subtype-specific product was inferred from the appearance of unique fragments when the product was digested with specific restriction enzymes. By using this RT-PCR method, products arising from mRNAs for all four brain sodium channel subtypes were identified in RNA extracted from adult rat cerebral cortex. The predominant component was type HA with lesser levels of types I,1, and m.In contrast, the type II and HA sequences were the predominant RT-PCR products in neonatal rat cortex, with slightly lower levels of type M and undetectable levels of type I. Thus, from neonate to adult, type H mRNA levels decrease relative to type HA levels. Using a similar approach, we detected mRfVA coding for the rat heart sodium channel in neonatal and adult rat cerebral cortex and in adult rat heart. These results reveal that mRNAs coding for the heart sodium channel and all four previously sequenced rat brain sodium channel subtypes are expressed in cerebral cortex and that type H and HA channels may be differentially regulated during development.Voltage-dependent sodium channels are responsible for action-potential generation and propagation in many excitable cells, including cardiac and skeletal muscle and neurons (1). Although virtually all sodium channels appear to have very similar functional properties, minor differences are observed among sodium channels from various cells in the same organism and, in some cases, within the same cell. One notable functional property that differs considerably among tissues is the sensitivity to the guanidinium toxins tetrodotoxin (TTX) and saxitoxin (STX). Sodium channels in central nervous system neurons and skeletal muscle are normally blocked by nanomolar concentrations of TTX and STX, whereas channels in cardiac cells and denervated skeletal muscle are relatively TTX/STX-resistant, requiring 0.1-10 AM toxin for block (2). Some cell types, including developing skeletal muscle myocytes (3-5), certain peripheral (dorsal root ganglion) neurons (6, 7), and some brain glial cells (astrocytes) (8-10), express both high-TTX-affinity and low-'ITX-affinity sodium channels. The physiological consequences of these differences are not known.Biochemical and molecular biological studies have provided considerable information about the molecular structures of voltage-gated ion channels. All sodium channels thus far characterized contain a large (260 kDa) a subunit and, in some cases, one or two smaller (30-40 kDa) p subunits (11-13). Hydropathy analysis of the primary amino acid sequence suggests that the a subunit consists of four homologous domains each containing six ...

Glial cells have heart: rH1 Na+ channel mRNA and protein in spinal cord astrocytes

“…that study, preliminary experiments noted heart-type Na ϩ channel ␣-subunit mRNA in primary cultures of rat cortical astrocytes (Yarowsky et al, 1991). Hartmann et al (1996) also detected a cardiac-like Na ϩ channel mRNA in limbic system structures from rat brain, and patch clamp studies have shown that entorhinal cortex (White et al, 1993) and septal neurons (Hartmann et al, 1996) express a Na ϩ current, which is Zn 2ϩ sensitive, similar to cardiac Na ϩ channels (Frelin et al, 1986;Ravindran et al, 1991;Visentin et al, 1990).…”

Identification of a novel voltage-gated Na+ channel rNav1.5a in the rat hippocampal progenitor stem cell line HiB5

“…In the periphery, rNa v 1.5 is expressed in denervated muscle [34] and in a peripheral neurotumourderived cell line RT4-B8 [53]. In the CNS rNa v 1.5 has been detected at the molecular level in rat cortex [52] and spinal cord astrocytes [4] and described functionally as well as molecularly in a neuroblastoma cell line [16]. rNa v 1.5 mRNA is thought to be restricted to the limbic region [17], which is the well-known epileptic focus for some types of seizures.…”

Distribution of voltage-gated sodium channel ?-subunit and ?-subunit mRNAs in human hippocampal formation, cortex, and cerebellum

“…Sodium channel ␣ and ␤ subunits show a defined temporal and spatial distribution in the rat central nervous system (CNS) revealed by immunoprecipitation (Gordon et al, 1987), Northern blot analysis (Beckh et al, 1989), reverse transcriptase-polymerase chain reaction (RT-PCR; Yarowsky et al, 1991), in situ hybridisation (Brysch et al, 1991;Furuyama et al, 1993;Black et al, 1994;Schaller et al, 1995;Felts et al, 1997;Gastaldi et al, 1997Gastaldi et al, , 1998Levy-Mozziconacci et al, 1998), and immunohistochemistry (Westenbroek et al, 1989). These studies show that the expression of sodium channel type I begins to increase after birth and, in the adult, is highest in caudal regions (e.g., colliculus and medulla pons) of the CNS.…”