Fig. 5. Stimulus-evoked action potentials revealed by current-clamp recordings from denervated muscle fibres. The amount of current injected was adjusted for each preparation to just reach the threshold at which action potentials were generated. (A) In females less than 5 days old, action potentials were non-overshooting with a moderate afterhyperpolarisation (left-hand panel). Muscles from females more than 18 days old generated overshooting action potentials with a pronounced afterhyperpolarisation (centre panel, see also B). In contrast, action potentials generated by fibres from females more than 18 days old treated with precocene resembled those from females less than 5 days old. (B) Action potentials from A shown on an expanded time scale for comparison. The action potential width for muscles of females more than 18 days old was increased. This increase was consistently absent from females treated with precocene. (C) Current injection evoked action potentials in fibres of muscle 169. Potentials from females less than 5 days old were non-overshooting and were followed by a small afterhyperpolarisation (C, left-hand panel). When females attained maturity, action potentials were overshooting but had still a small afterhyperpolarisation (C, centre panel). The action potentials of females treated with precocene were larger in amplitude than those of females less than 5 days old but were still non-overshooting. The afterhyperpolarisation of all groups was comparable (C, right-hand panel). (D) Potentials from C shown on an expanded time scale. The action potential width of mature female (untreated) muscle was increased.