Kv channels and the action potential. (a) Neuronal action potentials often last less than 10 ms, with an upstroke caused by influx and downstroke and undershoot caused by efflux. is the membrane potential. (b) Human ventricular myocyte action potentials last several hundred ms. The upstroke (0) is caused by influx, initial repolarization notch is caused by the transient outward current (), and the plateau phase is a balance between residual current, influx, and efflux (). Repolarization is primarily achieved by (mediated by KCNQ1-KCNE1 and possibly other KCNQ1-KCNE combinations) and . Inward rectifiers () help determine restingbetween action potentials. Upper right inset: surface electrocardiogram showing P wave, QRS complex, T wave, and QT interval. (c) Upper, cartoon of KCNQ1-KCNE complex; lower, topology diagram of KCNQ1 monomer. (d) Section through KCNQ1-KCNE complex showing main features. (e) Cartoon of voltage gating depicting the S4–S6 portions of a Kv subunit monomer and the type of conformational changes that may occur upon membrane depolarization.