Figure 2. β‐Adrenergic regulation of K⁺ channels during cardiac AP.

A, AP‐clamp Sequential Dissection experiments were performed as followed: steady‐state APs were recorded at a pacing rate of 1 Hz (upper panel), and used as the voltage command to obtain AP‐clamp recordings of the (three distinct) K⁺ currents in the same cell (middle panel) and the Ca²⁺ transients (lower panel) under physiological conditions. B, the effects of isoproterenol (ISO) on the AP waveform and the evoked K⁺ currents. At 30 nm, ISO significantly enhanced I _Ks, moderately increased I _K1, but slightly decreased I _Kr. C, D and E, concentration‐dependent effects of ISO on the peak densities of I _Ks, I _Kr and I _K1. F and G, the three K⁺ currents, measured in the same cell, were summed and each current was then normalized to this sum to calculate the relative contribution of each to the total K⁺ influx. The normalized current values at membrane potentials of +20 mV and −20 mV are shown in F and G, respectively. The ISO dose–response curves show how the relative contribution of each current shifts with various levels of β‐adrenergic stimulation. H, total K⁺ charge movement for individual K⁺ current and the sum of the currents during the AP. (Adapted from Banyasz et al. 2014 with permission.)