Fig. 2. Voltage-gated currents recorded from outer (A,B) and inner (C,D) muscle of 4–6 d.p.f. zebrafish larvae in normal physiological saline (Na⁺, K⁺, Ca²⁺ and Cl^– present). (A) Stepwise, 100 ms depolarizations from a range of potentials –85 to +50 mV (at 5 mV intervals) from a holding potential of –90 mV give rise to almost exclusively outwardly directed currents in voltage-clamped, outer muscle fibres. These currents show some evidence of an inactivating component. (B) Currents are evoked at potentials more positive to around –40 mV, and continue to increase with more depolarized potentials. (C) Similar voltage protocols applied, using the same salines, to inner zebrafish muscle evoke a pronounced, brief inward current (inset) followed by outwardly directed currents with a strong inactivating component. Current–voltage plots (D) of the peak amplitudes of the inward and outward currents reveal that inward currents are evoked at potentials more positive to around –40 mV, and outward currents more positive to around –20 mV. Filled symbols, outward currents; open symbols, inward currents.