Anti-minK Antisense Decreases the Amplitude of the Rapidly Activating Cardiac Delayed Rectifier K ⁺ Current

<jats:p> <jats:italic>Abstract</jats:italic> The rapidly and slowly activating delayed rectifier K <jats:sup>+</jats:sup> currents (I <jats:sub>Kr</jats:sub> and I <jats:sub>Ks</jats:sub> , respectively), which have different physiological properties, have been identified in cardiac cells from several species, including humans. Although expression of the minimal K <jats:sup>+</jats:sup> channel protein (minK) cDNA in some systems results in a current resembling I <jats:sub>Ks</jats:sub> , the role of this gene product in channel function remains controversial. In atrial tumor myocytes (AT-1 cells), no I <jats:sub>Ks</jats:sub> is recorded, but minK mRNA is detected, raising the possibility that expression of the minK gene serves an as-yet-unidentified function. In these experiments, AT-1 cells were exposed to antisense oligonucleotides targeting the 5′ translation start site of the minK cDNA cloned from an AT-1 library. Cell size, I <jats:sub>Kr</jats:sub> , and L-type and T-type Ca <jats:sup>2+</jats:sup> currents were measured 24 to 48 hours after exposure and compared with data in cells exposed to the corresponding sense oligonucleotide or grown in medium only. Antisense oligonucleotide significantly reduced I <jats:sub>Kr</jats:sub> compared with sense and medium-only control cells in 0 of 2 experiments (n=3 to 6 cells per treatment in each experiment) at 50 nmol/L, 1 of 2 at 250 nmol/L, 6 of 6 at 1000 nmol/L, and 2 of 2 at 10 000 nmol/L. At 1000 nmol/L, maximum tail current in antisense-exposed cells was 2.5±0.1 pA/pF (mean±SEM, n=28, 6 separate experiments), 6.6±0.4 pA/pF in sense-exposed cells (n=27), 5.4±0.6 pA/pF in medium-only cells (n=21), and 5.8±0.7 pA/pF in cells exposed to a random oligonucleotide (n=9). I <jats:sub>Kr</jats:sub> activation, rectification, deactivation, and sensitivity to the blocker dofetilide were unaffected. Two different antisense oligonucleotides produced the same effect, and there was no effect of antisense treatment on cell size or on L- or T-type Ca <jats:sup>2+</jats:sup> currents. These data indicate that in AT-1 cells, expression of the minK gene plays a role in determining I <jats:sub>Kr</jats:sub> amplitude. </jats:p>