Differential Sialylation Modulates Voltage-gated Na+ Channel Gating throughout the Developing Myocardium

Abstract

Voltage-gated sodium channel function from neonatal and adult rat cardiomyocytes was measured and compared. Channels from neonatal ventricles required an ∼10 mV greater depolarization for voltage-dependent gating events than did channels from neonatal atria and adult atria and ventricles. We questioned whether such gating shifts were due to developmental and/or chamber-dependent changes in channel-associated functional sialic acids. Thus, all gating characteristics for channels from neonatal atria and adult atria and ventricles shifted significantly to more depolarized potentials after removal of surface sialic acids. Desialylation of channels from neonatal ventricles did not affect channel gating. After removal of the complete surface N-glycosylation structures, gating of channels from neonatal atria and adult atria and ventricles shifted to depolarized potentials nearly identical to those measured for channels from neonatal ventricles. Gating of channels from neonatal ventricles were unaffected by such deglycosylation. Immunoblot gel shift analyses indicated that voltage-gated sodium channel α subunits from neonatal atria and adult atria and ventricles are more heavily sialylated than α subunits from neonatal ventricles. The data are consistent with approximately 15 more sialic acid residues attached to each α subunit from neonatal atria and adult atria and ventricles. The data indicate that differential sialylation of myocyte voltage-gated sodium channel α subunits is responsible for much of the developmental and chamber-specific remodeling of channel gating observed here. Further, cardiac excitability is likely impacted by these sialic acid–dependent gating effects, such as modulation of the rate of recovery from inactivation. A novel mechanism is described by which cardiac voltage-gated sodium channel gating and subsequently cardiac rhythms are modulated by changes in channel-associated sialic acids.

Regulated and aberrant glycosylation modulate cardiac electrical signaling

“…4, left panels). These data are consistent with our previous report indicating Na v sialylation impacts channel gating in the neonatal atrium but not in the neonatal ventricle (15). These data also correlate with the AP data.…”

“…To determine whether the remodeled glycome modulates cardiac function, we observed the impact of the regulated and aberrant expression of a single glycogene on cardiomyocyte electrical activity. We studied the effect of the polysialyltransferase, ST8sia2 (responsible for addition of sialic acid polymers to N-and O-glycans), on cardiac function for several reasons that include: (i) Cardiac dysfunctions including arrhythmias and cardiomyopathy that are likely caused by changes in ion channel activity are prevalent in diseases of aberrant sialylation such as Chagas disease and some CDGs (16 -19); (ii) all our previous data indicated that changes in ion channel sialylation contribute significantly to the modulation of ion channel function (11)(12)(13)15); and (iii) cardiac ST8sia2 expression is regulated. ST8sia2 is expressed at much higher levels in the neonatal atrium than in the neonatal ventricle as determined through microarray ( Fig.…”

“…Neonatal cardiomyocytes were isolated as described previously (15). APs were recorded at room temperature using an Axopatch 200B amplifier (Axon Instruments) and pCLAMP software (Axon Instruments).…”

“…Recording solutions were described previously (9). Na v recordings were performed as described previously (15).…”

“…Most studies established that the sugar-dependent gating effects were imposed by the terminal residue attached to carbohydrate structures, sialic acid. A recent work showed that variable sialic acid levels attached to a single Na v isoform, Na v 1.5, were responsible for differences in channel gating observed among neonatal and adult atrial and ventricular cardiomyocytes (15).…”