The electric potential change of internal membrane during propagation of contraction in skinned fibre of toad skeletal muscle.

With skinned fibres prepared by removing sarcolemma in liquid paraffin from single fibres isolated from m. adductor magnus, m. sartorius or m. rectus internus major of toad (Bufo bufo japonicus), it was determined whether or not an action potential ("internal action potential", or IAP) could be detected during a propagated contraction evoked by electrical square pulses of 1 msec duration. The IAP less than 10 mV was recorded with a glass capillary microelectrode inserted into the skinned fibre during a contraction propagating along the skinned fibre. The shape of the IAP was similar to the action potential of a surface membrane of the skeletal muscle fibre, although its time course was far slower. The rate of rise of IAP was more rapid than that of the mechanical movement which was measured by the change in scattered light quantity of a gas-laser beam. When a contraction wave was propagated as far as the unskinned portion it reflected there and began to propagate backwards along the skinned portion. Whenever a contraction wave passed through the microelectrode-inserted portion, the IAP was recorded. When the propagation of a contraction wave was blocked somewhere in the skinned fibre, a potential change in reverse direction was recorded there. The phase of this potential change corresponded with the after potential of the IAP.