Tubulin polymerization modifies cardiac sodium channel expression and gating.
OBJECTIVE
Treatment with the anticancer drug taxol (TXL), which polymerizes the cytoskeleton protein tubulin, may evoke cardiac arrhythmias based on reduced human cardiac sodium channel (Na(v)1.5) function. Therefore, we investigated whether enhanced tubulin polymerization by TXL affects Na(v)1.5 function and expression and whether these effects are beta1-subunit-mediated.


RESULTS
Human embryonic kidney (HEK293) cells, transfected with SCN5A cDNA alone (Na(v)1.5) or together with SCN1B cDNA (Na(v)1.5 + beta1), and neonatal rat cardiomyocytes (NRCs) were incubated in the presence and in the absence of 100 microM TXL. Sodium current (I(Na)) characteristics were studied using patch-clamp techniques. Na(v)1.5 membrane expression was determined by immunocytochemistry and confocal microscopy. Pre-treatment with TXL reduced peak I(Na) amplitude nearly two-fold in both Na(v)1.5 and Na(v)1.5 + beta1, as well as in NRCs, compared with untreated cells. Accordingly, HEK293 cells and NRCs stained with anti-Na(v)1.5 antibody revealed a reduced membrane-labelling intensity in the TXL-treated groups. In addition, TXL accelerated I(Na) decay of Na(v)1.5 + beta1, whereas I(Na) decay of Na(v)1.5 remained unaltered. Finally, TXL reduced the fraction of channels that slow inactivated from 31% to 18%, and increased the time constant of slow inactivation by two-fold in Na(v)1.5. Conversely, slow inactivation properties of Na(v)1.5 + beta1 were unchanged by TXL.


CONCLUSIONS
Enhanced tubulin polymerization reduces sarcolemmal Na(v)1.5 expression and I(Na) amplitude in a beta1-subunit-independent fashion and causes I(Na) fast and slow inactivation impairment in a beta1-subunit-dependent way. These changes may underlie conduction-slowing-dependent cardiac arrhythmias under conditions of enhanced tubulin polymerization, e.g. TXL treatment and heart failure.
Casini
Simona
S
Department of Clinical and Experimental Cardiology, Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
Tan
Hanno L
HL
Demirayak
Ilker
I
Remme
Carol Ann
CA
Amin
Ahmad S
AS
Scicluna
Brendon P
BP
Chatyan
Houssine
H
Ruijter
Jan M
JM
Bezzina
Connie R
CR
van Ginneken
Antoni C G
AC
Veldkamp
Marieke W
MW
D000818:Animals; D000831:Animals, Newborn; D001145:Arrhythmias, Cardiac / Q000378:metabolism / Q000503:physiopathology; D002460:Cell Line; D006801:Humans; D007150:Immunohistochemistry; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007668:Kidney / Q000166:cytology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D017239:Paclitaxel / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011108:Polymers / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection; D014404:Tubulin / Q000378:metabolism*; D050257:Tubulin Modulators / Q000494:pharmacology; D062547:Voltage-Gated Sodium Channel beta-1 Subunit
D008565:Membrane Proteins; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011108:Polymers; C470379:SCN1B protein, human; C568320:SCN5A protein, human; C568322:Scn5a protein, rat; D015222:Sodium Channels; D014404:Tubulin; D050257:Tubulin Modulators; D062547:Voltage-Gated Sodium Channel beta-1 Subunit; D017239:Paclitaxel