ERG K channel blockade enhances firing and epinephrine secretion in rat chromaffin cells: the missing link to LQT2-related sudden death?

The ether-a-go-go-related genes (erg) are expressed in tissues other than heart and brain, in which human erg (HERG) K+ channels are known to regulate the repolarization of heart action potentials and neuronal spike-frequency accommodation. We provide evidence that erg1 transcripts and ERG proteins are present in rat chromaffin cells in which we could isolate a K+ current that was biophysically and pharmacologically similar to the ERG current. Firing frequency and catecholamine release were analyzed at the single-cell level by means of perforated patch-clamp and carbon fiber electrochemical detection. It was found that the blocking of ERG, KATP, and KCa channels led to hyperexcitability and an increase in catecholamine release. Combined immunocytochemical experiments with antibodies directed against phenylethanolamine N-methyltransferase and ERG channels suggested expression of these channels in epinephrine- but not in norepinephrine-containing cells. It is concluded that, in addition to being crucial in regulating the QT period in the heart, ERG channels play a role in modulating epinephrine, a fundamental neurotransmitter shaping cardiac function. This finding suggests that the sudden death phenotype associated with LQT2 syndrome mutations may be the result of an emotionally triggered increase in epinephrine in a long-QT running heart.