Molecular identity of the late sodium current in adult dog cardiomyocytes identified by Nav1.5 antisense inhibition.
Late Na(+) current (I(NaL)) is a major component of the action potential plateau in human and canine myocardium. Since I(NaL) is increased in heart failure and ischemia, it represents a novel potential target for cardioprotection. However, the molecular identity of I(NaL) remains unclear. We tested the hypothesis that the cardiac Na(+) channel isoform (Na(v)1.5) is a major contributor to I(NaL) in adult dog ventricular cardiomyocytes (VCs). Cultured VCs were exposed to an antisense morpholino-based oligonucleotide (Na(v)1.5 asOligo) targeting the region around the start codon of Na(v)1.5 mRNA or a control nonsense oligonucleotide (nsOligo). Densities of both transient Na(+) current (I(NaT)) and I(NaL) (both in pA/pF) were monitored by whole cell patch clamp. In HEK293 cells expressing Na(v)1.5 or Na(v)1.2, Na(v)1.5 asOligo specifically silenced functional expression of Na(v)1.5 (up to 60% of the initial I(NaT)) but not Na(v)1.2. In both nsOligo-treated controls and untreated VCs, I(NaT) and I(NaL) remained unchanged for up to 5 days. However, both I(NaT) and I(NaL) decreased exponentially with similar time courses (tau = 46 and 56 h, respectively) after VCs were treated with Na(v)1.5 asOligo without changes in 1) decay kinetics, 2) steady-state activation and inactivation, and 3) the ratio of I(NaL) to I(NaT). Four days after exposure to Na(v)1.5 asOligo, I(NaT) and I(NaL) amounted to 68 +/- 6% (mean +/- SE; n = 20, P < 0.01) and 60 +/- 7% (n = 11, P < 0.018) of those in VCs treated by nsOligo, respectively. We conclude that in adult dog heart Na(v)1.5 sodium channels have a "functional half-life" of approximately 35 h (0.69tau) and make a major contribution to I(NaL).
Department of Internal Medicine, Henry Ford Hospital, Cardiovascular Research, Education & Research Bldg. Rm. 4015, 2799 West Grand Blvd., Detroit, MI 48202-2689, USA.
Victor A
VA
Maltsev
John W
JW
Kyle
Sudhish
S
Mishra
Abertas
A
Undrovinas
D000818:Animals; D002478:Cells, Cultured; D004285:Dogs; D020868:Gene Silencing; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials; D008955:Models, Cardiovascular; D009025:Morpholines / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D009025:Morpholines; D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D015222:Sodium Channels; D012964:Sodium