Repetitive firing of light-triggered APs in Xenopus oocytes coexpressing either neuronal Na_v1.2, skeletal muscle Na_v1.4, or cardiac Na_v1.5 with β1-ChR2 and K_v2.1. The membrane potential was set to −80 mV (Na_v1.2 or Na_v1.5) or −85 mV (Na_v1.4), and the change of membrane voltage was followed in the current-clamp mode on 50-ms light pulses every 2 s.