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We investigated the contribution of sialic acid residues to the [K.sup.+] currents involved in the repolarization of mouse ventricular myocytes. Ventricular [K.sup.+] currents had a rapidly inactivating component followed by slowly decaying and sustained components. This current was produced by the summation of three distinct currents: [I.sub.to], which contributed to the transient component; [I.sub.ss], which contributed to the sustained component; and [I.sub.K,slow], which contributed to both components. Incubation of ventricular myocytes with the sialidase neuraminidase reduced the amplitude of [I.sub.to] without altering [I.sub.K,slow] and [I.sub.ss]. We found that the reduction in [I.sub.to] amplitude resulted from a depolarizing shift in the voltage of activation and a reduction in the conductance of [I.sub.to]. Expression of Kv4.3 channels, a major contributor to [I.sub.to] in the ventricle, in a sialylation-deficient Chinese hamster ovary cell line (lec2) mimicked the effects of neuraminidase on the ventricular [I.sub.to]. Furthermore, we showed that sialylated glycolipids have little effect on the voltage dependence of [I.sub.to]. Finally, consistent with its actions on [I.sub.to], neuraminidase produced an increase in the duration of the action potential of ventricular myocytes and the frequency of early afterdepolarizations. We conclude that sialylation of the proteins forming Kv4 channels is important in determining the voltage dependence and conductance of [I.sub.to] and that incomplete glycosylation of these channels could lead to arrhythmias. glycosylation; Kv4.3; arrhythmias; mouse ventricular myocytes; transient outward currents

Investigates the contribution of sialic acid residues to the potassium currents involved in the repolarization of mouse ventricular myocytes. Physiological effect of potassium current levels; Production of potassium current through the summary of three distinct currents; Contribution to voltage dependence of transient current component of potassium.

Investigates the role of sialic acid residues in the function of potassium channels involved in the repolarization of the mouse ventricle. Suggestion that the channels underlying currents in the mouse ventricle vary in regard to the number of sialic acid residues attached to them during posttranslational processing; Arrhythmogenic currents to the transient component resulting from improper glycosylation of Kv4 channels.