Predicting hERG repolarization power at 37°C from recordings at room temperature
Mutations in the KCNH2 gene cause long or short QT syndromes (LQTS or SQTS) predisposing to life-threatening arrhythmias. KCNH2 encodes for the voltage-gated K+ channel hERG involved in the late repolarization phase of the cardiac action potential (AP). For the last decades, sequencing KCNH2 has provided a plethora of variants associated or not with clear pathological cardiac phenotypes. Identifying pathogenic or likely pathogenic variants from the benign ones would provide useful information to clarify the genetic background of LQTS patients and relatives, and to stratify the risk of adverse events. In face of a wide spectrum of hERG biophysical defects, we looked for a way to summarize the net loss or gain of function in a unique index. In a previous work, we defined as the repolarization power the time integral of the K+ currents developed during an AP clamp. Here, with the aim of accelerating the functional characterization of hERG variants using automated patch-clamp, we adapted the AP-clamp protocol to establish, at room temperature, at which the recording success rate is high, a repolarization power index, as reliable and informative as the one measured at physiological temperature. We also illustrate that the repolarization power determined at room temperature is predictive of the repolarization power at physiological temperature for 2 pathogenic hERG variants with different biophysical dysfunctions.