Fig. 6. (A) Steady-state activation and inactivation of putative K⁺ currents of 4–6 d.p.f. zebrafish inner muscle. Steady-state activation (filled circles; N=7) was determined by applying a series of 5 ms activating pulses from a holding potential of –100 mV to a range of potentials from –45 to +65 mV at 5 mV intervals (inset, right). These pulses were followed immediately by a step to –130 mV to enable the measurement of tail currents. The amplitudes of the tails were normalised to a maximum value of 1 and plotted against the amplitude of the activating pulse. Steady state inactivation (open circles; N=6) was determined as in Fig. 3C (inset, left). (B) These outwardly directed currents are blocked by 10 µmol l^–1 4-aminopyridine (4AP) in a use-dependent manner. Stepwise 250 ms depolarizations from a holding potential of 100 mV to a potential of 0 mV were applied as the larva was perfused in saline containing 10 µmol l^–1 4AP. Numbers indicate the sequence of depolarizing pulses.