Fig. 5. Isolation of K⁺ currents from inner and outer muscle of 4–6 d.p.f. zebrafish larvae was performed by applying depolarizing pulses to voltage-clamped fibres in saline in which all sodium ions were replaced with equimolar choline ions and all calcium ions were replaced with equimolar cadmium ions and supplemented with BAPTA (10 mmol l^–1). (A) K⁺ currents of outer muscle. A series of 250 ms depolarizations from a holding potential of –100 mV to a range of potentials from –95 to 25 mV evoked outwardly directed currents with little or no evidence of inactivation. (B) A current–voltage plot of such currents shows that they appear at membrane potentials more positive to around –40 mV and increase with more positive potentials. (C) K⁺ currents of inner muscle. (D) The current–voltage plot of these currents reveals that they are activated at potentials more positive than around –20 mV. There is still some residual inward current. Values are means ± S.E.M. of at least eight separate experiments