Open AccessMolecular cloning of a putative tetrodotoxin-resistant rat heart Na+ channel isoform.
Author(s) -
R. B. Rogart,
Leanne L. Cribbs,
Louis Muglia,
Daniel D. Kephart,
Maja Kaiser
Publication year - 1989
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.86.20.8170
Subject(s) - gene isoform , tetrodotoxin , skeletal muscle , biology , cdna library , complementary dna , microbiology and biotechnology , sodium channel , cardiac muscle , denervation , molecular cloning , gene , endocrinology , biochemistry , chemistry , sodium , organic chemistry
Voltage-gated Na+ channels in mammalian heart differ from those in nerve and skeletal muscle. One major difference is that tetrodotoxin (TTX)-resistant cardiac Na+ channels are blocked by 1-10 microM TTX, whereas TTX-sensitive nerve Na+ channels are blocked by nanomolar TTX concentrations. We constructed a cDNA library from 6-day-old rat hearts, where only low-affinity [3H]saxitoxin receptors, corresponding to TTX-resistant Na+ channels, were detected. We isolated several overlapping cDNA clones encompassing 7542 nucleotides and encoding the entire alpha subunit of a cardiac-specific Na+ channel isoform (designated rat heart I) as well as several rat brain I Na+ channel cDNA clones. The derived amino acid sequence of rat heart I was highly homologous to, but distinct from, previous Na+ channel clones. RNase protection studies showed that the corresponding mRNA species is abundant in newborn and adult rat hearts, but not detectable in brain or innervated skeletal muscle. The same mRNA species appears upon denervation of skeletal muscle, likely accounting for expression of new TTX-resistant Na+ channels. Thus, this cardiac-specific Na+ channel clone appears to encode a distinct TTX-resistant isoform and is another member of the mammalian Na+ channel multigene family, found in newborn heart and denervated skeletal muscles.