Tubulin polymerization modifies cardiac sodium channel expression and gating

Abstract

AimsTreatment with the anticancer drug taxol (TXL), which polymerizes the cytoskeleton protein tubulin, may evoke cardiac arrhythmias based on reduced human cardiac sodium channel (Nav1.5) function. Therefore, we investigated whether enhanced tubulin polymerization by TXL affects Na v1.5 function and expression and whether these effects are β1-subunit-mediated.Methods and resultsHuman embryonic kidney (HEK293) cells, transfected with SCN5A cDNA alone (Nav1.5) or together with SCN1B cDNA (Nav1.5 +β1), and neonatal rat cardiomyocytes (NRCs) were incubated in the presence and in the absence of 100μ M TXL. Sodium current (INa) characteristics were studied using patch-clamp techniques. Nav1.5 membrane expression was determined by immunocytochemistry and confocal microscopy. Pre-treatment with TXL reduced peak INa amplitude nearly two-fold in both Nav1.5 and Nav1.5 + 1, as well as in NRCs, compared with untreated cells. Accordingly, HEK293 cells and NRCs stained with anti-Nav1.5 antibody revealed a reduced membrane-labelling intensity in the TXL-treated groups. In addition, TXL accelerated INa decay of Nav1.5 +β1, whereas I Na decay of Nav1.5 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 Nav1.5. Conversely, slow INactivation properties of Nav1.5 +β1 were unchanged by TXL.ConclusionEnhanced tubulin polymerization reduces sarcolemmal Nav1.5 expression and INa amplitude in a 1-subunit-independent fashion and causes INa fast and slow INactivation impairment in a β1-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.