A, OGB-5N transients, recorded from a normal FDB fibre, elicited by voltage steps (from a holding potential of −90 mV) to −60, −40 and 0 mV. Fibre diameter: 32 μm. B, OGB-5N transients elicited by identical voltage steps to those in A, but from an mdx FDB fibre. Fibre diameter: 29 μm. In both cases Cs+ internal solution and 0 Na+ Tyrode were used.