Antisense oligodeoxynucleotides directed against Kv1.5 mRNA specifically inhibit ultrarapid delayed rectifier K+ current in cultured adult human atrial myocytes

Several cloned K+ channel subunits are candidates to underlie macroscopic currents in the human heart, but direct evidence bearing on their role is lacking. The Kv1.5 K+ channel subunit has been suggested to play a potential role in human cardiac ultrarapid delayed rectifier (I-Kur) and transient outward (I-to) currents. To evaluate the role of proteins encoded by the Kv1.5 gene, we incubated cultured human atrial myocytes for 48 hours in medium containing antisense phosphorothioate oligodeoxynucleotides directed against octodecameric segments of the Kv1.5 mRNA coding sequence, the same concentration of homologous oligodeoxynucleotides with four mismatch mutations, or vehicle (control group). Cells exposed to antisense showed a highly significant (approximate to 50%) reduction in I-Kur, whether measured by step current at the end of a 400-millisecond depolarizing pulse, tail current at -20 mV, or current sensitive to a concentration of 4-aminopyridine (50 mu mol/L) that is highly selective for I-Kur, compared with control cells or cells exposed to mismatch oligodeoxynucleotides. In contrast, I-to was not different among the three experimental groups. When cultured human ventricular myocytes were exposed to Kv1.5 antisense oligodeoxynucleotides with the same controls, no changes occurred in either I-to or the sustained current at the end of a depolarizing pulse. We conclude that Kv1.5 channel subunits are essential to the expression of I-Kur and do not play a role in I-to in cultured human atrial myocytes. These studies provide the first direct evidence with an antisense approach for the equivalence between a macroscopic cardiac K+ current and a cloned K+ channel subunit and offer insights into the molecular electrophysiology of the human heart.